Distributer vacuum tube missing...?
Discussion
griff59 said:
Belle427 said:
You should get it checked but in reality it probably won’t make a huge difference by reconnecting it yourself.
The issue is that it could cause detonation/pinking which is almost impossible to hear on these engines and is a bad thing if left like this.
Yet another reply that confirms my doubts about this whole thing. It's like having the ever so slightly cracked sound board replaced in my grand piano just because an expert said it would make a huge difference to the way the instrument sounded, and played, even though it sounds great and plays superbly to me. I've had a few piano technicians around and all gave conflicting opinions, the last guy said if it plays well and if you like the sound leave well alone, I'm adopting the same attitude with my Griff. The issue is that it could cause detonation/pinking which is almost impossible to hear on these engines and is a bad thing if left like this.
What's confusing me about your above response is if you have doubts about this whole thing why are you still contributing to the post and why did you buy the hose? Don't be critical of something you don't understand, no one said this is something you can do without engaging your brain to understand they whys and hows.
It seems you're doubting the validity of something many have have seen success with because you're being advised to check your timing first, Belle427 is just giving you good advice. All he's saying is you should always check what you're doing and measure the changes you've made, this is just common sense, if common sense and proceeding with caution is a pain for you my advice is simply... 'do not proceed at all'.
The only risk would be if switching to full manifold vacuum added timing when the engine was under load, this of course is impossible because when you're accelerating there's little or no vacuum to act on the vacuum advance unit, so it will be adding nothing. The truth is when you take the time understand how the system works you'll soon realise the the vacuum advance unit only adds timing at idle and cruise, and in both cases the engine is under little or no load so there's really no risk of detonation. But that doesn't mean you shouldn't check what you're doing and measure the timing changes you're making by switching to manifold vacuum, that's just common sense!
There seems to be either an underlying inability or perhaps an unwillingness understand the theory here which has been very clearly explained, if this rings true perhaps you should accept making changes to your car is not for you. If you're not completely confident in what you're doing and why, and you're not prepared to do some basic ignition timing checks when you switch to full manifold vacuum my best advice would be to leave it alone and let others enjoy the benefits.
If your real frustration here is this isn't quite as simple as unplugging your brain and blindly moving a hose from one place to another without putting the minimum effort in to understand exactly what you're doing and why you're doing it in the first place.... then maybe it's best to accept it's not for you.
Assuming you're confident to progress here's a useful post from Belle427 explaining his switch from ported to full manifold vacuum.
But if understanding it all is a pain, if reading and digesting all the facts gives you a headache, then you could just read the above results published by others who've made the switch. But I still recommend you try to absorb the facts before you proceed and you also check and record your ignition timing before and after you've made the switch. In life it's never a good idea to do anything without first properly understanding exactly why you're doing it in the first place.... and why it gives the results it does.
By switching to full manifold vacuum Belle427 showed us he picked up 6 degrees and StuVT picked up 10 degrees at idle, both only ever saw the 18 degrees of mechanical advance the distributor gives on top of their idle timing number recorded with the vacuum advance disconnected!, the distributor will stop advancing at 3,000rpm so there's no point in revving the engine higher when conducting your all out timing tests.
Usefully StuVT also tells us as he un-clamped the vac advance pipe full manifold vacuum lifted his idle speed by 350rpm from 600rpm to 950rpm, he also shows us at cruise the vacuum advance adds 10 degrees of timing taking his all out mechanical advance figure of 26 degrees to 36 degrees, but only under high vacuum cruise conditions and at 3,000rpm and above. When StuVT is accelerating his throttle will be open so the vacuum inside the plenum will be lost, with little or no vacuum acting on the vacuum advance unit it will be adding nothing so his total timing at 3,000rpm and above will be safely back to 26 degrees.
Follow the checks completed by Belle427 and StuVT and record your numbers, both guys have understood what they are doing and have completed the change in the correct way by proving what happens when you switch from ported vacuum to full manifold vacuum. Neither have just guessed, they've taken to correct approach and have clearly shared their findings for the benefit of all, this is exactly how the PH forum is meant to work!
Belle427 said:
My findings are
12 degrees btdc static.
Full manifold vacuum, adding 6 degrees at idle so its roughly 18 degrees btdc.
Total timing all in 30 degrees.
As already mentioned you need to check your timing figures before carrying it out.
Every car will be different.
And here's his results....12 degrees btdc static.
Full manifold vacuum, adding 6 degrees at idle so its roughly 18 degrees btdc.
Total timing all in 30 degrees.
As already mentioned you need to check your timing figures before carrying it out.
Every car will be different.
Belle427 said:
Ive noticed improved low speed driveability, better mpg and cooler running temps since switching. The car is a lot more responsive low down, feels like its gained more torque. Running temp also down by roughly 10 degrees on the gauge.
Cant see a down side to this modification.
And here's a similar post from StuVT who also made the switch.Cant see a down side to this modification.
StuVT said:
Idle 8deg BTDC vac OFF which with
full vacuum the figure is 18deg BTDC. Vacuum taken from the plenum take off that was used by the fuel fume purge device.
This gives 26deg full mechanical advance at 3500rpm+ and around 36deg vac and mechanical for cruise.
Base idle set to 600rpm, which gave 950rpm with the bypass hose unclamped.
PcV fitted to the flame trap.
Fuel purge equipment removed.
All breather hoses jubilee clipped.
And here's his results....full vacuum the figure is 18deg BTDC. Vacuum taken from the plenum take off that was used by the fuel fume purge device.
This gives 26deg full mechanical advance at 3500rpm+ and around 36deg vac and mechanical for cruise.
Base idle set to 600rpm, which gave 950rpm with the bypass hose unclamped.
PcV fitted to the flame trap.
Fuel purge equipment removed.
All breather hoses jubilee clipped.
StuVT said:
I finally got out today and it was a bit odd actually looking for traffic.
Anyway I am a convert. After letting it warm up I found a steep hill near Whipsnade Zoo and couldn't detect any pinging, all noises were regular and I have a slight blow on a V clamp for the Y piece but that is a regular sound and is always there, but at 26 full mech advance I doubt pinging will be an issue. I need to make some new det cans. Mine were rather perished and not ear worthy.....
I cruised the town centre where I know traffic builds.
The car is definately calmer to drive like this. There is a hint of shunting but its only slight and after a while I didnt notice it. It would cruise at 30mph in 4th at idle and in 1st and 2nd I got the revs to between 1200 and 1800 and changed the throttle position to stimulate slow traffic. This is where the possible diluted shunt, like a slight hesitation manifests itself.
I'm considering moving the distributor to the 22btdc mark I made at idle to see if this cures the slight hesitation. But to be honest where it is now is fine. I cruised the town centre traffic for an hour and it was relaxed and I actually enjoyed it. Before it was like river dance in the clutch and throttle to keep it smooth.
I know its arctic out there but the temp was just under 90c the whole time.
On the open road it pulls from idle up to the limiter smoothly and goes like a stabbed rat!
Off the national speed limit roads back into the town traffic and it stayed just below 90c and continued to crawl in traffic rather civilised again.
The only issue thats unchanged is the shift from 1st to 2nd is jerky. It may be me or a thing they all do, but I hoped this was connected with shunting.
Overall, very happy with it. So much calmer to drive in town.
ChimpOnGas - Thank you for sharing your findings.
Im seriously considering having the distributor modded to mimic your ignition curves at some point this year if you would be happy to share. Stu
And finally from chris212Anyway I am a convert. After letting it warm up I found a steep hill near Whipsnade Zoo and couldn't detect any pinging, all noises were regular and I have a slight blow on a V clamp for the Y piece but that is a regular sound and is always there, but at 26 full mech advance I doubt pinging will be an issue. I need to make some new det cans. Mine were rather perished and not ear worthy.....
I cruised the town centre where I know traffic builds.
The car is definately calmer to drive like this. There is a hint of shunting but its only slight and after a while I didnt notice it. It would cruise at 30mph in 4th at idle and in 1st and 2nd I got the revs to between 1200 and 1800 and changed the throttle position to stimulate slow traffic. This is where the possible diluted shunt, like a slight hesitation manifests itself.
I'm considering moving the distributor to the 22btdc mark I made at idle to see if this cures the slight hesitation. But to be honest where it is now is fine. I cruised the town centre traffic for an hour and it was relaxed and I actually enjoyed it. Before it was like river dance in the clutch and throttle to keep it smooth.
I know its arctic out there but the temp was just under 90c the whole time.
On the open road it pulls from idle up to the limiter smoothly and goes like a stabbed rat!
Off the national speed limit roads back into the town traffic and it stayed just below 90c and continued to crawl in traffic rather civilised again.
The only issue thats unchanged is the shift from 1st to 2nd is jerky. It may be me or a thing they all do, but I hoped this was connected with shunting.
Overall, very happy with it. So much calmer to drive in town.
ChimpOnGas - Thank you for sharing your findings.
Im seriously considering having the distributor modded to mimic your ignition curves at some point this year if you would be happy to share. Stu
chris212 said:
I've noticed an improvement since going manifold vacuum. The shunting has virtually gone.
As instructed by ConG, I ran a t-piece from the fuel regulator and used the original pipe with the one way valve to the advance. Checked the timing and that was it.
I've suffered shunting since I've had it (8 years) and this is the best improvement towards eradicating it. With the vac advance disconnected, its as it was (shunting)
Unlike people who recommend disconnecting the vacuum advance completely (which is a stupid idea), I would never recommend something without offering detailed supporting evidence covering the science behind why and how the changes work. As instructed by ConG, I ran a t-piece from the fuel regulator and used the original pipe with the one way valve to the advance. Checked the timing and that was it.
I've suffered shunting since I've had it (8 years) and this is the best improvement towards eradicating it. With the vac advance disconnected, its as it was (shunting)
But if understanding it all is a pain, if reading and digesting all the facts gives you a headache, then you could just read the above results published by others who've made the switch. But I still recommend you try to absorb the facts before you proceed and you also check and record your ignition timing before and after you've made the switch. In life it's never a good idea to do anything without first properly understanding exactly why you're doing it in the first place.... and why it gives the results it does.
By switching to full manifold vacuum Belle427 showed us he picked up 6 degrees and StuVT picked up 10 degrees at idle, both only ever saw the 18 degrees of mechanical advance the distributor gives on top of their idle timing number recorded with the vacuum advance disconnected!, the distributor will stop advancing at 3,000rpm so there's no point in revving the engine higher when conducting your all out timing tests.
Usefully StuVT also tells us as he un-clamped the vac advance pipe full manifold vacuum lifted his idle speed by 350rpm from 600rpm to 950rpm, he also shows us at cruise the vacuum advance adds 10 degrees of timing taking his all out mechanical advance figure of 26 degrees to 36 degrees, but only under high vacuum cruise conditions and at 3,000rpm and above. When StuVT is accelerating his throttle will be open so the vacuum inside the plenum will be lost, with little or no vacuum acting on the vacuum advance unit it will be adding nothing so his total timing at 3,000rpm and above will be safely back to 26 degrees.
Follow the checks completed by Belle427 and StuVT and record your numbers, both guys have understood what they are doing and have completed the change in the correct way by proving what happens when you switch from ported vacuum to full manifold vacuum. Neither have just guessed, they've taken to correct approach and have clearly shared their findings for the benefit of all, this is exactly how the PH forum is meant to work!
ChimpOnGas said:
If buying a strobe and learning how to use it to check your ignition timing scares you, please step away now, are you really trying say you don't know how to check your timing?
What's confusing me about your above response is if you have doubts about this whole thing why are you still contributing to the post and why did you buy the hose? Don't be critical of something you don't understand, no one said this is something you can do without engaging your brain to understand they whys and hows.
It seems you're doubting the validity of something many have have seen success with because you're being advised to check your timing first, Belle427 is just giving you good advice. All he's saying is you should always check what you're doing and measure the changes you've made, this is just common sense, if common sense and proceeding with caution is a pain for you my advice is simply... 'do not proceed at all'.
The only risk would be if switching to full manifold vacuum added timing when the engine was under load, this of course is impossible because when you're accelerating there's little or no vacuum to act on the vacuum advance unit, so it will be adding nothing. The truth is when you take the time understand how the system works you'll soon realise the the vacuum advance unit only adds timing at idle and cruise, and in both cases the engine is under little or no load so there's really no risk of detonation. But that doesn't mean you shouldn't check what you're doing and measure the timing changes you're making by switching to manifold vacuum, that's just common sense!
There seems to be either an underlying inability or perhaps an unwillingness understand the theory here which has been very clearly explained, if this rings true perhaps you should accept making changes to your car is not for you. If you're not completely confident in what you're doing and why, and you're not prepared to do some basic ignition timing checks when you switch to full manifold vacuum my best advice would be to leave it alone and let others enjoy the benefits.
If your real frustration here is this isn't quite as simple as unplugging your brain and blindly moving a hose from one place to another without putting the minimum effort in to understand exactly what you're doing and why you're doing it in the first place.... then maybe it's best to accept it's not for you.
You're absolutely right, I should step away now. But my mind is open, I am willing to try the hose based on your advice, but it's best if I leave it to a TVR mechanic, if it was just a case of fitting the hose even I could do that, but it seems more involved. I used to work on my cars when I was younger, but for some reason I've lost all of my confidence to do even the most basic things now.What's confusing me about your above response is if you have doubts about this whole thing why are you still contributing to the post and why did you buy the hose? Don't be critical of something you don't understand, no one said this is something you can do without engaging your brain to understand they whys and hows.
It seems you're doubting the validity of something many have have seen success with because you're being advised to check your timing first, Belle427 is just giving you good advice. All he's saying is you should always check what you're doing and measure the changes you've made, this is just common sense, if common sense and proceeding with caution is a pain for you my advice is simply... 'do not proceed at all'.
The only risk would be if switching to full manifold vacuum added timing when the engine was under load, this of course is impossible because when you're accelerating there's little or no vacuum to act on the vacuum advance unit, so it will be adding nothing. The truth is when you take the time understand how the system works you'll soon realise the the vacuum advance unit only adds timing at idle and cruise, and in both cases the engine is under little or no load so there's really no risk of detonation. But that doesn't mean you shouldn't check what you're doing and measure the timing changes you're making by switching to manifold vacuum, that's just common sense!
There seems to be either an underlying inability or perhaps an unwillingness understand the theory here which has been very clearly explained, if this rings true perhaps you should accept making changes to your car is not for you. If you're not completely confident in what you're doing and why, and you're not prepared to do some basic ignition timing checks when you switch to full manifold vacuum my best advice would be to leave it alone and let others enjoy the benefits.
If your real frustration here is this isn't quite as simple as unplugging your brain and blindly moving a hose from one place to another without putting the minimum effort in to understand exactly what you're doing and why you're doing it in the first place.... then maybe it's best to accept it's not for you.
I initially connected mine without checking the timing as my strobe was mia, not ideal but my right foot had a tremendous itch to scratch.
I took it for a gentle test drive, avoiding large hills and larger throttle openings and all was well.
Minor adjustments were made when i obtained a strobe.
In reality your timing may be at 8 to 12 btdc at the moment, maybe chimpongas can confirm but adding vac advance to this should still see you at safe levels.
I took it for a gentle test drive, avoiding large hills and larger throttle openings and all was well.
Minor adjustments were made when i obtained a strobe.
In reality your timing may be at 8 to 12 btdc at the moment, maybe chimpongas can confirm but adding vac advance to this should still see you at safe levels.
Belle427 said:
I initially connected mine without checking the timing as my strobe was mia, not ideal but my right foot had a tremendous itch to scratch.
I took it for a gentle test drive, avoiding large hills and larger throttle openings and all was well.
Minor adjustments were made when i obtained a strobe.
In reality your timing may be at 8 to 12 btdc at the moment, maybe chimpongas can confirm but adding vac advance to this should still see you at safe levels.
Thanks a lot, that's all I wanted to know, just wondering what you found when you got your strobe?I took it for a gentle test drive, avoiding large hills and larger throttle openings and all was well.
Minor adjustments were made when i obtained a strobe.
In reality your timing may be at 8 to 12 btdc at the moment, maybe chimpongas can confirm but adding vac advance to this should still see you at safe levels.
Hi all,
What a great thread, I will carry out the change to direct vacuum tomorrow, the car is to hot under the bonnet at present.
I had to re time the car as I took the dizzy out to prime the oil pump, I have confirmed TDC, a wooden BBQ skewer in plug hole one and rotated the engine from the bottom pulley until the point where the piston had stopped travel either way, and set the idle at 12 degrees BTDC.
I had the emissions checked and the car was running rich at idle, used rover gauge and saw a lamba sensor not working, found a loose connection and all seems good, I re set the ECU and have been out for a blast. the car drives very well but hunts a little at idle, I removed plug one and it still seems to still be running rich, will the direct vacuum modification smooth out idle, and possibly help the running rich?
I have fitted a new air filter, MAF readings on rover gauge seem spot on and engine temperature sensor seems fine, reading roughly the same as in car gauge and fan kicking in and out ok. Short term fuel trim fluctuation from -20% to + 20 on both banks.
Many thanks as always
What a great thread, I will carry out the change to direct vacuum tomorrow, the car is to hot under the bonnet at present.
I had to re time the car as I took the dizzy out to prime the oil pump, I have confirmed TDC, a wooden BBQ skewer in plug hole one and rotated the engine from the bottom pulley until the point where the piston had stopped travel either way, and set the idle at 12 degrees BTDC.
I had the emissions checked and the car was running rich at idle, used rover gauge and saw a lamba sensor not working, found a loose connection and all seems good, I re set the ECU and have been out for a blast. the car drives very well but hunts a little at idle, I removed plug one and it still seems to still be running rich, will the direct vacuum modification smooth out idle, and possibly help the running rich?
I have fitted a new air filter, MAF readings on rover gauge seem spot on and engine temperature sensor seems fine, reading roughly the same as in car gauge and fan kicking in and out ok. Short term fuel trim fluctuation from -20% to + 20 on both banks.
Many thanks as always
Franky boy said:
Hi all,
What a great thread, I will carry out the change to direct vacuum tomorrow, the car is to hot under the bonnet at present.
Hi Frank, one of the key advantages of running more advance at idle is your under bonnet temps will be significantly reduced, as is my way I will not just make this sweeping statement and run for the hills, I will take the time to explain the science behind why you will experience this reduction in exhaust heat and other benefits.What a great thread, I will carry out the change to direct vacuum tomorrow, the car is to hot under the bonnet at present.
An internal combustion engine makes torque (power) by producing heat, the more heat you can extract from a given amount of fuel the more efficient your engine will be, however it's even more important what you do with this precious heat once you've made it. The efficient harnessing of the heat you've made is the very essence of engine efficiency, our objective should be to harness 100% of the heat extracted from the chemical energy (fuel) and make it do work to produce torque (power). Internal combustion engines are actually very poor at using this heat to make torque (power), only 25% of the heat goes to create torque (power) the rest is effectively just thrown away!
As we can see from the above graphic 30% of our valuable heat is absorbed by the coolant/oil and a whopping 40% of our precious heat goes straight out of the exhaust to heat it and the atmosphere we live in, this is why we've just had huge delays on the Euro Tunnel. The Euro Tunnel trains have big air conditioning units that under normal circumstances extract the crazy amounts of heat each loading car brings with it onto the carriage, if the trains didn't have air conditioning temperatures would rise beyond what the human body could tolerate so these systems are more important than you think. Unfortunately hot weather means hotter cars and because the atmosphere is starting out hotter the system reached critical mass, basically the designers of the Euro Tunnel train air conditioning system failed to build in sufficient head-space to cover the sustained high temperatures we've been having of late, in simple terms they got their sums wrong.
Anyway back to our cars which as you may have noticed make a ton of heat especially under the bonnet, this isn't heat used to make torque (power) and produce forward motion, what you're feeling when you open your bonnet is that highly inefficient process of throwing all that valuable heat you paid for at the pump straight into the exhaust. Think about your house and it's central heating system, your central heating system is meant to keep your house and it's occupants warm and you pay a hefty privilege for this in inflated Russian gas prices, knowing this none of us open our front door and all our windows in the depths of winter as we know it would be wasteful. Ported vacuum ensures your TVR is idling at 10-12 degrees which is just like opening your doors and windows in your house because your exhaust valves will start to open long before all that lovely heat in your combustion gasses have fully acted on your piston crowns.
If you're the kind of guy who opens his front door and all your windows on the coldest day with your central heating of full blast then you're the kind of guy who'll love ported vacuum and the 10-12 degrees of idle timing it gives, however if like me you like to close all your doors and windows in the winter months then you'll absolutely love running full vacuum on your TVR too
With the standard idle timing of 10-12 degrees the exhaust valves are starting to open long before we've extracted the full benefit of the heat these valuable gasses produce, these hot combustion gasses pass the open exhaust valves and into the exhaust system. While it seems illogical and counteractive to have the exhaust valves still open before the valuable combustion gasses have given their maximum work Land Rover and others actually did this for a reason, all that heat being thrown into the exhaust system was used to rapidly heat up the catalytic converters as they will only start to work above a certain temperature. This retarded idle strategy was a common trick used by car makers from the early 70's right through to the early/mid 90's, it was especially useful on old inefficient engine designs like the Rover V8 because it's a cheap to implement sticking plaster solution to an issue that really needed addressing by designing a new and more modern and efficient engine which of course is hugely costly.
But my illogical and counteractive point remains very relevant here, the problem is with this 10-12 degrees emissions improving idle timing strategy is it's quite clearly extremely inefficient use of fuel, just like opening the doors and windows of your house in the winter would be ridiculously inefficient! It doesn't take a genius to realise just how inefficient it is to be taking so much of the heat generated by your lovey valuable combustion gasses and throwing it straight out of an open exhaust port, it's blindingly obvious our objective should be to utilise as much of these magical heat generating and precious combustion gas to make torque (power).
When you make the simple and free switch to full manifold vacuum what you're doing is initiating combustion earlier in the cycle at the same engine speed, as an air fuel mixture is chemical energy it has a fixed burn time which does not change. Advancing your timing is simply lighting the (fixed burn speed) fire earlier, this gives more time for the air/fuel charge to burn completely before your exhaust valves start to open, the burn is therefore more complete and more of your combustion gasses and the heat they generate is now going towards the production of torque (power) and forward motion rather than some of it being used to create two very effective pot belly stoves that are your TVR's exhaust manifolds.
When you apply a full manifold signal to your vac advance unit you'll find your idle timing will increase from your current 12 degrees BTDC to somewhere in the order of 18-20 degrees, effectively you are lighting the fire some 8 degrees of crankshaft rotation earlier giving more time for the combustion gasses to push down on the piston crown before your exhaust valves start to open!
Congratulations... you've just closed the doors and windows of your centrally heated house on the coldest winter day
On full manifold vacuum a considerable percentage more of your heat producing combustion gasses are now being used to push your pistons down to produce torque (power) and forward motion, compare this with the standard 10-12 degrees idle timing that uses a far bigger percentage of your expensive fuel simply to make heat in the manifolds and light the cats.
If after switching to manifold vacuum you put your car on a dyno this increase in torque at idle and just off idle would be quite evident, dynos are not just for measuring peak torque and horspower figures at wide open throttle so you can brag about how much power your TVR makes when you get down the pub. Used correctly a dyno can and should be used to measure the production of torque (horsepower is just a function of torque) at many points of engine speed vs engine load, this should include idle and just off idle as this is the biggest contributor to drivability.
Idle and just off idle tuning is not a sexy topic, but there's a reason why car makers spend so much time on it, nothing will give you a greater improvement in drivability than deeply focusing your attention on that very narrow band between 900-1,200rpm. Actually there are two key ways you can influence torque, the fist is to alter your air fuel ratio (AFR or what we used to call mixtures), and the second is how and when you burn that AFR in the cycle. The thing is from a lean 14.7:1 idle AFR to a richer 13.0:1 you may only see a 1-2% increase in torque if you're lucky, this immediately exposes the folly of expensive 14CUX chip tuning, now consider the difference between the standard 10-12 degrees of idle timing vs your new vac advance assisted 18 degrees and you may see as much as an 8-10% increase in torque at idle and in that split second just off idle as you pull away.
So, a 1-2% increase at idle and just off idle from a richer AFR £400 Mark Adams chip, or as much as an 8-10% increase in torque at idle and in that split second just off idle as you pull away from idle, and simply by switching your vac advance unit to a full manifold signal which of course is completely free. If you're looking for drivability improvements from you expensive MA chip my advice is save your money, you will make a massively greater improvement with ignition timing than any fuel change could ever hope to offer and it costs you nothing too, this is the very definition of a no-brainer!
It actually matters little if you have access to a dyno or not because I absolutely guarantee you will feel it, where before you might need to apply a small throttle opening to initiate the pull away you will now find you can just lift your foot off the clutch to initiate the first split second of forward motion. While this new big bubble of torque only exists for that split second it actually makes a huge difference to drivability, you can enhance the effect further by raising your idle speed from the standard 950rpm to 1050rpm. The second thing you'll notice moving to full manifold vacuum is the engine will lose that nasty fluffy misfire point just off idle as you pull away most Chimaeras and Griffiths seem to exhibit, this is generated by the rapid on/off ignition timing ported vacuum inflicts on the engine as the throttle butterfly passes back and forth over the port, as you pull away the standard arrangement is actually bouncing from no vacuum to full manifold vacuum and back to no vacuum over and over which can also contribute to shunting.
While you're enjoying your new 'Float Away' TVR take moment to listen to the engine at idle too, you will find your idle is now smoother and because the combustion process produces noise as well as heat you'll notice your idle is quieter too. No longer are you throwing heat into the open exhaust system you're also no longer throwing noise there too. The quieter idle is especially relevant and noticeable with our cars because they dont have cast iron exhaust manifolds like a Range Rover/Discovery, which are excellent noise suppressors in themselves. The TVRs tube manifolds offer extremely poor noise suppression and the design is made even worse by the big voids used to house the cats, any reduction in noise will be quite noticeable and in my opinion most welcome because while the V8 noise emanating from your tailpipes is pure joy, general engine bay noise just makes a car sound rough and unrefined.
Franky boy said:
I had to re time the car as I took the dizzy out to prime the oil pump, I have confirmed TDC, a wooden BBQ skewer in plug hole one and rotated the engine from the bottom pulley until the point where the piston had stopped travel either way, and set the idle at 12 degrees BTDC.
Great work Frank, this is the only 100% sure fired way to establish your true TDC point, setting the idle at 12 degrees BTDC is also spot on. The distributor will add 18 degrees of mechanical advance on top of your now totally proven and confirmed 12 degrees of idle timing, so that's 12 + 18 = 30 degrees of total timing which is both detonation safe and good for peak power. Do keep in mind the distributor is all done by roughly 2,800rpm anyway, at which point full mechanical advance is achieved, when switching to full manifold vacuum you'll find your vacuum advance unit will immediately add 8-10 degrees of timing at idle, so your 12 degrees BTDC plus the 8-10 degrees becomes a nice heat and torque efficient 18-20 degrees but only at idle where sufficient vacuum exists in the plenum and inlet manifold to act on your vac advance to give you that additional 8-10 degrees of timing at idle and just off idle as you pull away. Press harder on the throttle pedal and vacuum rapidly falls away so you'll still end up with your totally safe 30 degrees of total timing, as you ease back off and settle into cruising on the motorway you're now closing your throttle butterfly and so the vacuum in your plenum/inlet manifold starts to rise again. You'll now be buzzing along at 75mph at 2,800rpm with the distributor give all its got at 30 degrees, but on top of this and because vacuum is high the vac advance is now adding an additional 10 degrees of timing, you're now cruising along at 40 degrees of total timing which at cruise will help you reduce your fuel consumption by 5% or more.
Actually this cruise figure of 40 degrees will be exactly the same with ported vacuum, the only benefit area when switching to full manifold vacuum is at idle and just off idle when you pull away, there may also be a small benefit further up the rev range and below 2,000rpm but it will be a diminishing reward from idle up to that point. Ported vacuum is of course full manifold vacuum most of the time but that doesn't meant you're not going to enjoy real and very noticeable benefits by making the switch, because that tiny RPM vs Load band at idle and just off idle as you pull away is more important to the way the car feels than you could ever imagine.
Franky boy said:
I had the emissions checked and the car was running rich at idle, used rover gauge and saw a lamba sensor not working, found a loose connection and all seems good, I re set the ECU and have been out for a blast. the car drives very well but hunts a little at idle, I removed plug one and it still seems to still be running rich, will the direct vacuum modification smooth out idle, and possibly help the running rich?
And this is where running full manifold vacuum is not going to help, when you make the switch I'm afraid to say you'll only ever see a negative impact in your emissions. Saying that the Rover V8 is a very inefficient engine with very poor airflow, add in a typical TVR cam profile and you've got a recipe for high emissions, of course the more aggressive the cam profile the more ignition advance you need to run at idle so while the accepted thinking is more timing at idle will increase your emissions you may actually find this is balanced out by the fact your new 18 degrees of idle timing will be far better suited to your more aggressive camshaft. If you are still running cats and you're emissions are high with the current 12 degrees of idle timing I strongly recommend you turn your attentions towards making sure your ignition system is in rude health.That means spark plugs, HT leads and especially those dreadful failure prone spark plug extenders that are a common source of misfires. At this point it's important to accept even the very best and most efficient modern internal combustion engines misfire, try not to think about it as eliminating all your misfires because you'll never ever achieve that, you need to focus on reducing their frequency. The most effective way to reduce misfires on our cars is to take those dreadful spark plug extenders and throw them in the bin, with a good set of HT leads well protected with socks you really dont need them either.
Finally if you're still running the shrouded electrode No7 heat range spark plugs these need to go too, replace with a set of NGK BPR6ES which are far more suitable or better still their iridium brothers. Those original No7 plugs chosen by TVR are way too cold for road use so they tend to readily foul, and a fouled plug will increase the frequency and quantity of misfires dramatically making the switch to BPR6ES or better still a set of BPR6EIX iridium plugs one of the best things you can do to improve idle emissions and idle quality next to deleting those nasty extenders.
With new quality and well protected HT leads, the heat extenders removed and a set of BPR6EIX iridium plugs fitted you'll be making big improvements. Now switch to full manifold vacuum to idle at 18 degrees and it'll be the cherry on the cake, the extra timing will add engine speed in the order of 200-300rpm so you will need to wind it back down with your base idle screw but that's only a good thing as it's really just a vacuum leak which we should always seek to reduce/eliminate wherever possible when tuning for a smooth and stable idle. Using timing to manage idle speed is always preferable to using an air bleed, not only do you go leaner when you add air which demands a fuel compensation strategy from the ECU, but when compared with ignition timing an engine is very slow to respond to air changes initiated by an idle valve (stepper motor), ignition timing has a close to immediate impact which is exactly what you want.
https://www.youtube.com/watch?v=kiPow6aeb_0
Finally with all the above completed dont forget to come back to this post to share your findings as others have already done, the forum is only any good if people take the time to share their experiences
Dave.
Hi again,
I've teed the vacuum into the fuel regulator vacuum pipe and checked timing and gone for a short drive, my findings so far are:
Without the vac advance connected to the distributor Im still reading 12degrees BTDC, when connected I'm getting 20 degrees at idle.
The car seems to pull very well and would say better at low revs, I found an incline and tried to drive up it in a high gear, absolutely no sign of pinking.
The idle speed does not really seemed to have changed, and still hunts between 950-1050.
As far as under bonnet temperature changing is concerned it is difficult to tell, I think my heater valve must be stuck as even with the roof of it can be unbearable hot in the cabin.
I need to re fit the cross member, removed to get a socket on the bottom pulley, and give the car a longer run. I'm racing this weekend (not the TVR) so may have to be next week.
Is the ecu intelligent enough to "learn" or does it just react to the information it receives?
Cheers once again.
I've teed the vacuum into the fuel regulator vacuum pipe and checked timing and gone for a short drive, my findings so far are:
Without the vac advance connected to the distributor Im still reading 12degrees BTDC, when connected I'm getting 20 degrees at idle.
The car seems to pull very well and would say better at low revs, I found an incline and tried to drive up it in a high gear, absolutely no sign of pinking.
The idle speed does not really seemed to have changed, and still hunts between 950-1050.
As far as under bonnet temperature changing is concerned it is difficult to tell, I think my heater valve must be stuck as even with the roof of it can be unbearable hot in the cabin.
I need to re fit the cross member, removed to get a socket on the bottom pulley, and give the car a longer run. I'm racing this weekend (not the TVR) so may have to be next week.
Is the ecu intelligent enough to "learn" or does it just react to the information it receives?
Cheers once again.
^^^^^^
Franky, you may find this 'concise' overview of use:
http://www.autospeed.com/cms/article.html?&tit...
... especially:
If the engine runs closed loop fuel control at idle, too much idle timing advance can disrupt the oxygen sensor reading, causing the self-learning process to overly enrich the idle mixture. Setting the optimal ignition timing can therefore best be done by trial and error variations.
The 14CUX ECU does indeed use adaptive fuelling software for establishing both short- and term-term fuel adjustment values.
I have experienced cranking issues on my car when dialling in too much static advance (more than 12 degrees) and using the standard ported vacuum advance setup.
Franky, you may find this 'concise' overview of use:
http://www.autospeed.com/cms/article.html?&tit...
... especially:
If the engine runs closed loop fuel control at idle, too much idle timing advance can disrupt the oxygen sensor reading, causing the self-learning process to overly enrich the idle mixture. Setting the optimal ignition timing can therefore best be done by trial and error variations.
The 14CUX ECU does indeed use adaptive fuelling software for establishing both short- and term-term fuel adjustment values.
I have experienced cranking issues on my car when dialling in too much static advance (more than 12 degrees) and using the standard ported vacuum advance setup.
Edited by davep on Thursday 2nd August 16:05
Franky boy said:
Hi again,
I've teed the vacuum into the fuel regulator vacuum pipe and checked timing and gone for a short drive, without the vac advance connected to the distributor Im still reading 12degrees BTDC, when connected I'm getting 20 degrees at idle.
The car seems to pull very well and would say better at low revs
That sounds very much like you're feeling the same benefits others are enjoying, and based on the feedback so far it would seem a pattern of reported evidence is forming here from multiple, independent, and unconnected contributors who've experimented with switching to full vacuum and have no reason other than to truthfully report whatever they find.... good or bad!I've teed the vacuum into the fuel regulator vacuum pipe and checked timing and gone for a short drive, without the vac advance connected to the distributor Im still reading 12degrees BTDC, when connected I'm getting 20 degrees at idle.
The car seems to pull very well and would say better at low revs
It's probably just a coincidence
Or is it
blitzracing said:
Ill also vouch for this modification, the only change apart from moving the pipe was to drop the base idle. It did not pass the HC test on MOT as expected, but just a case of using the original set up just for the MOT.
Belle427 said:
Car is a lot more responsive low down, feels like its gained more torque.
StuVT said:
I am a convert. The car is definately calmer to drive like this, I cruised the town centre traffic for an hour and it was relaxed and I actually enjoyed it. Before it was like river dance in the clutch and throttle to keep it smooth. Overall, very happy with it. So much calmer to drive in town. Thank you for sharing your findings.Stu
chris212 said:
I've noticed an improvement since going manifold vacuum. The shunting has virtually gone.As instructed by ConG, I ran a t-piece piece from the fuel regulator and used the original pipe with the one way valve to the advance. Checked the timing and that was it. I've suffered shunting since I've had it (8 years) and this is the best improvement towards eradicating it. With the vac advance disconnected, its as it was ( shunting).Mine is a 4.3 precat.
Including Franky boy's latest feedback that's five clear positive results so far and nothing negative at all reported from switching to full manifold vacuum, like I say it's probably just a coincidence 
To the five converts I say "Enjoy"
To the doubting Thomas' I say "Study the science, read the evidence, take a more open minded approach and try it, what have you got to lose"
It's free, takes five minutes, and if you don't like the results it's 100% reversible just as easily too
ChimpOnGas said:
Including Franky boy's latest feedback that's five clear positive results so far and nothing negative at all reported from switching to full manifold vacuum, like I say it's probably just a coincidence
To the five converts I say "Enjoy"
To the doubting Thomas' I say "Study the science, read the evidence, take a more open minded approach and try it, what have you got to lose"
It's free, takes five minutes, and if you don't like the results it's 100% reversible just as easily too
I'm going to book the car in for a check up soon, I'll get him to fit the hose and check the timing, I'm suffering from a bit of shunting, and rough tick-over, especially after long runs, this might not have anything to do with the hose but after reading people's replies here, it's worth putting it back to see if it improves things. To the five converts I say "Enjoy"
To the doubting Thomas' I say "Study the science, read the evidence, take a more open minded approach and try it, what have you got to lose"
It's free, takes five minutes, and if you don't like the results it's 100% reversible just as easily too
ChimpOnGas, I'm working my way through your info, and even though I don' understand most of it, the positive replies from others means it's got to worth trying.
Full vac feedback....
Replaced the broken vac unit & retimed (new unit must hold the baseplate in a slightly different position)
Timing 10 Deg BTDC ported vac
Timing 22 Deg BTDC full vac
Left base idle screw alone or time being
Ported vac trial- Noticeable improvement over no vac, less low rpm heositancy.
Full vac trial - same reduction in low spec hesitancy, smoother idle, subjectively less heat billowing out when sat idling on driveway doing checks.
Rovergauge indicates idle bypass nearly shut whereas ~35% on ported. Also idling on less fuel indicated by fuel map site.
Edited to say my neighbour who knows nothing about cars just said "that sounds different, a lot smoother, what have you done?" When it was idling in the drive just now.
Replaced the broken vac unit & retimed (new unit must hold the baseplate in a slightly different position)
Timing 10 Deg BTDC ported vac
Timing 22 Deg BTDC full vac
Left base idle screw alone or time being
Ported vac trial- Noticeable improvement over no vac, less low rpm heositancy.
Full vac trial - same reduction in low spec hesitancy, smoother idle, subjectively less heat billowing out when sat idling on driveway doing checks.
Rovergauge indicates idle bypass nearly shut whereas ~35% on ported. Also idling on less fuel indicated by fuel map site.
Edited to say my neighbour who knows nothing about cars just said "that sounds different, a lot smoother, what have you done?" When it was idling in the drive just now.
Edited by Kev Bamber on Thursday 9th August 18:19
Kev Bamber said:
Full vac feedback....Same reduction in low spec hesitancy, smoother idle, subjectively less heat billowing out when sat idling on driveway doing checks.
Excellent Kev Bamber said:
Rovergauge indicates idle bypass nearly shut whereas ~35% on ported.
This is because your new advanced timing number of 22 degrees has raised your idle by 300rpm or so, you don't see or hear this because the ECU immediately corrects the situation by closing the stepper motor reducing the air bleed and so returning your idle to the 950rpm target. This is a good thing as it'll help (along with the new advanced idle timing) to give you sharper throttle response just off idle as you pull away. Going back a step the reason your idle has gone up when you switched to full vacuum is because you're now extracting more energy from your air fuel mix, and doing so more efficiently by initiating combustion earlier which is exactly what the engine wants!Kev Bamber said:
Also idling on less fuel indicated by fuel map site.
Less air requires less fuel to achieve the same target 14.7:1 air fuel ratio (AFR) the 14CUX system is constantly shooting for, lighting that mixture a full 12 degrees of crankshaft rotation earlier gives more time for it to burn completely in the combustion chamber before the exhaust valves start open. This effectively means you are harnessing more heat energy from the fuel using it to push down on your piston crowns and ultimately turn your crankshaft, rather than inefficiently throwing a percentage of that valuable energy out of the open exhaust valves to super heat the exhaust manifolds as when you were initiating combustion only 10 degrees of crankshaft rotation before the piston reaches top dead centre.Kev Bamber said:
My neighbor who knows nothing about cars just said "that sounds different, a lot smoother, what have you done?" When it was idling in the drive.
What your neighbor is hearing here is a happier engine, because you're now harnessing a greater percentage of valuable heat energy and converting it into work (torque) the engine is now running smoother, the precious heat energy you were previously throwing away into your exhaust manifolds also carried acoustic energy. You probably wouldn't notice this much on a Range Rover with cast iron manifolds that run down the sides of the block, but by comparison the TVR's tube manifolds offer little in the way of acoustic insulation and their positioning high in the engine bay compounds this further. Running 12 degrees more advance at idle will not only give you a smoother idle it should be a quieter idle too, when these two elements are combined the effect is even people who know nothing of cars and engine tuning will naturally hear it which is why your neighbor responded with their positive and unprompted comment.It would seem overall you've achieved some great results here so thanks for sharing, this is another clear positive result to add to all the others, the simple to implement and completely free switch to full manifold vacuum is clearly gaining significant popularity. Just remember this change has one drawback, running more advance at idle will very likely mean a fail at MoT time, resolving the issue is of course no more difficult than switching back to ported vacuum
As we can see from the above graph CO is not the problem, but the further we advance the timing the higher the NOx and HCs figures go.
This is actually the one and only reason engineers in the early 70's came up with the ported vacuum idea, essentially it ensures the benefits of the vacuum advance are still enjoyed at cruise while also giving the emissions friendly retarded idle timing. The elephant in the room is that if you're not burdened by trying to meet emissions targets and your only focus is to achieve the smoothest running engine you would never run ported vacuum and 10 degrees at idle especially on a RV8 TVR with their typically more aggressive camshafts, and I'll explain this important camshaft element later.
I strongly suspect the reason Japanese market MG RV8s were delivered with full manifold vacuum was because in the 1990's the Japanese emissions standards were really rather lax at the time, seeing this the engineers at Rover took the opportunity to ditch the dreadful US & European emissions driven ported vacuum setup and ran the Jap market RV8s on the far superior full manifold setup.
It's a significant source of amusement to me the truth about ported vacuum has all been revealed to you all in a post where the ignorant were actually promoting (without evidence or scientific fact) the concept of completely removing the vacuum advance hose altogether
. If anyone is thinking of doing this please reconsider as it's the dumbest idea ever, once people properly understand the Otto Cycle and how a four stroke engine actually works this will become clear as day. 1. Intake stroke - The falling piston creates a depression drawing fuel and air drawn into the combustion chamber
2. Compression stroke - The fuel and air is compressed raising the pressure in the combustion chamber, but also creating heat!
NB: Watch this compression generated heat, if it's too high it can cause auto ignition of the fuel air mixture before you've initiated combustion intentionally with your ignition system, a violent and destructive condition known as detonation (pinking) will follow, this is very bad news so we must avoid it at all costs!
3. Combustion (Not a Stroke) - Initiation of the progressive burn of the fuel and air at a chosen number of degrees of crankshaft rotation before the piston reaches top dead centre (BTDC)
4. Power stroke - Expanding super heated gasses from the burning fuel and air mix pushes on the crown of the piston, the reciprocal motion is converted into rotational motion at the crankshaft
5. Exhaust stroke - At this point the piston is on the way back up the bore so it pushes remaining combustion products out of chamber
Before anyone says the five points should be four because the above is showing a four stroke engine, it's important you understand point 3 (combustion) is not a stroke. Combustion is however an critical element in the process, clearly when it occurs needs to be precisely controlled as this will have a huge effect on how efficiently the valuable heat energy from your burning fuel and air mix is harnessed.
At this point it's important to understand that fuel is just chemical energy, but to make use of this energy we must first unlock it to turn it into heat (the burn). Now as fuel is chemical energy it burns at a fixed speed so it stands to reason the faster the engine is going through the four cycles the earlier we will need it initiate combustion to give the fixed burn speed fuel time to burn completely and to deliver it's maximum work. As engine speed increases we initiate combustion with a spark from the spark plug earlier and earlier to give the fuel more and more time to burn the fixed burn speed fuel to burn completely, this is what we're doing when we advance our ignition timing, basically we're just making sure we light the fire earlier and earlier the faster the engine spins.
The next thing we need to consider is valve timing, this is dictated by the profile of your camshaft lobes which dictates how long your valves stay open in the cycle, but also their positioning in relationship to each other.... or in other words how far they are separated from each other which is why we refer to this element as lobe separation.
While studying the four cycles/strokes of a for stroke engine one might logically assume we want our exhaust and inlet valves to snap open and shut precisely at top or bottom dead centre and never be open together at the same time, however in reality this is actually not the case at all
The truth is there are significant advantages in playing with valve timing, for instance while it seems counter intuitive to have both the inlet and exhaust valves open at the same time what actually happens when you do this is rather than all that lovely fuel and air mix just flying straight out into the open exhausts, the inertia of the escaping exhaust gasses is harnessed to draw in more air and fuel into the combustion chamber. The effect is kind of a free forced induction system in reverse, the cam plays a big part but so does the length and shape of the exhaust system/manifolds which on a catted Chim or Griff is very poorly designed indeed for exhaust gas extraction!
Exhaust system/manifold design aside we call the practice of keeping both the inlet and exhaust valves open at the same time 'Valve Overlap', valve overlap is dictated by your valve timing which as we now know is dictated by our camshaft. Obviously there's a limit to how long we can keep both inlet and exhaust valves open at the same time before we do indeed start losing some of that valuable fuel and air mix straight out of the exhaust, and the truth is the effects of valve overlap are directly linked to engine speed just as ignition timing is directly linked to engine speed.
At low engine speeds exhaust speeds are low too, so keeping both inlet and exhaust valves open at the same time for too long is typically a bad idea because exhaust gas inertia is low so the benefits are lost, indeed the effects are undesirable. However, as engine speed increases the exhaust gasses start to move faster and faster, the effect of these faster moving exhaust gasses is to pull in the new fresh charge of fuel and air, the faster the engine spins the greater the benefits of valve overlap become (up to a point). So we can now see how a valve timing and overlap arrangement that works super efficiently at say 3,500rpm is going to work very badly at 1,000rpm, basically valve timing is always going to be a compromise which is precisely why we have variable valve timing on modern engines.
This is also why engines with aggressive camshafts go like stink above a certain engine speed but will always come with the compromise of a ragged idle and poor engine behavior at low speeds. A milder cam as used in Range Rovers will give a lovely smooth idle and good slow speed drivability but poor performance at higher engine speeds, while the more aggressive camshaft grinds used in TVRs fitted with what amounts to the same engine will give fantastic cylinder filling and performance at higher engine speeds, but at the sacrifice of poor idle quality and low speed engine behavior. Remember this poor low engine speed behavior generated by a more aggressive cam is further exacerbated by the poor design of the TVR Chimaera and Griffith 'catted' exhaust manifolds, Pre-Cat Griffs with their long tube headers are way better in this respect by the way.
All this sounds like our cars with our more aggressive cam profiles are stuck with poor idle quality, but fear not, there are things we can do to help
. If you're running lots of valve overlap you'll have a ragged idle and poor drivability at low engine speeds for sure, but what if you initiate the burn of your air and fuel earlier at idle so more of it is used to push your piston down before it flys out of the open exhaust when running all that valve overlap that works so well at higher engine speeds? We'll this is exactly what we do, and it's another reason why full manifold vacuum works so well on TVRs because typically our camshafts run way more overlap than the profiles used in Range Rovers.Up to a point the more aggressive your valve timing is and the more overlap you run, the more ignition advance you need to run at idle, running a Range Rover with it's mild cam at 10-12 degrees of ignition advance may well work just fine, but apply it to a RV8 TVR with a more progressive cam with way more valve overlap and initiating combustion at 10-12 degrees of crankshaft rotation before top dead centre is simply way too late. However, switch your TVR to full manifold vacuum and you're now lighting the fire a full 10 degrees earlier (20-22 degrees BTC) at idle giving a lot more time to burn your valuable fuel and air mix before you start throwing some of it out of the exhaust to just to heat the manifolds (as used by designers in the 70s & 80s to light the cats in the emissions friendly ported vacuum 10-12 degrees idle timing).
So hopefully you can now see why a RV8 TVRs with their poor exhaust manifold design and more aggressive cam profiles respond so well to running more advance at idle, and why running a full manifold signal to your vacuum advance unit that delivers this extra 10 degrees of timing is delivering the positive results reported by so mny who've already tried it. What we've done here is understand the four cycles of an internal combustion engine, valve timing, and the effects of ignition timing on your engine. This is a far superior and infinitely more intelligent approach than simply quoting your TVR specialistswho's trying to convince you....
"Disconnect your vac advance hose is what performance engines need"
Hopefully everyone now can see why disconnecting your vac advance hose on your TVR is the stupidest idea ever, what you actually want to do is apply more ignition advance at idle on a TVR that typically runs an aggressive cam duration and overlap and suffers poor exhaust manifold design... NOT LESS
There really are some poorly educated and misinformed people out there giving bad advice in the TVR world, don't be sucked in by their fancy websites, their self appointed 'TVR Specialist' status and their TVR sign over their door. Anyone can claim to be an expert but I'd encourage you all to educate yourselves first, then armed with the power of knowledge challenge these so called experts on why they think disconnecting the vac advance is such a clever idea
I guarantee you they will stumble and stutter some BS answer at you, an answer that now you've properly armed yourselves with the facts and knowledge you'll instantly be able to unpick and discredit using simple fact and logic
Belle427 said:
I initially connected mine without checking the timing as my strobe was mia, not ideal but my right foot had a tremendous itch to scratch.
I took it for a gentle test drive, avoiding large hills and larger throttle openings and all was well.
Minor adjustments were made when i obtained a strobe.
In reality your timing may be at 8 to 12 btdc at the moment, maybe chimpongas can confirm but adding vac advance to this should still see you at safe levels.
I'm going to reconnect the hose today, maybe ChimpOnGas can advise if it's OK to temporarily do this without checking the timing? I took it for a gentle test drive, avoiding large hills and larger throttle openings and all was well.
Minor adjustments were made when i obtained a strobe.
In reality your timing may be at 8 to 12 btdc at the moment, maybe chimpongas can confirm but adding vac advance to this should still see you at safe levels.
Thread continuation.
Bought a 4ltr Precat in April.
No problems with the running, idle perhaps a little high so I cleaned the stepper motor, better but creeps up slightly when idling hot, and I'm wondering if what I found below might contribute by way of an air leak?
While checking it over I noticed the vacuum hose connection where it pushes onto the dizzy was split apart and therfore not sealing at all.
I've got some new pipe but noticed when fitting it to the dizzy and sucking on it to test the vacuum canister there is no vacuum, ie no pull on the tongue after using it to seal the tube.
Are the vac' adv' units still available?
BTW I checked my spare Dizzy off the Chim' and that's buggered as well.
Cheers
Bought a 4ltr Precat in April.
No problems with the running, idle perhaps a little high so I cleaned the stepper motor, better but creeps up slightly when idling hot, and I'm wondering if what I found below might contribute by way of an air leak?
While checking it over I noticed the vacuum hose connection where it pushes onto the dizzy was split apart and therfore not sealing at all.
I've got some new pipe but noticed when fitting it to the dizzy and sucking on it to test the vacuum canister there is no vacuum, ie no pull on the tongue after using it to seal the tube.
Are the vac' adv' units still available?
BTW I checked my spare Dizzy off the Chim' and that's buggered as well.
Cheers
On further checking I've found that the vent stub on the auto' vac' unit is capped, so I'm assuming the diaphragm failed sometime in the
past and rather than replaced the unit the engine was run without auto' adv' working but connected to the plenum.
Anyway found a source and going to replace it.
My Spitty was one of the rare cars fitted from new with a dizzy without a vacuum unit, never found out why.
past and rather than replaced the unit the engine was run without auto' adv' working but connected to the plenum.
Anyway found a source and going to replace it.
My Spitty was one of the rare cars fitted from new with a dizzy without a vacuum unit, never found out why.
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