Throttle Pot sourcing
Discussion
It may also help to see the sort of ignition timing numbers you can run if you have the flexibility of a fully mapable distributorless ignition system that offers three dimensional ignition control. No longer held back by the limitations imposed by the distributor that to the most part only advances timing in a linear fashion in relation to engine speed we can now give the engine what it really wants.
While you may not be able to achieve these numbers with your distributor the following map will hopefully help distributor people see why it would be utter madness to disconnect their vacuum advance unit (see point 4 below for more detail), it is after all the nearest thing you have to 3D ignition timing control.
Studying the above map there are some interesting takeaways:
1. The blue cell shows us where the engine idles.... at 1,000rpm at a load of 45kPa combustion is being initiated at 18 degrees of crankshaft rotation before top dead centre, compare this with the emissions based 10 degrees a standard distributor Chimaera would be running on ported vacuum. Trust me if 10 degrees was best we would see 10 in that blue cell because changing it from 18 to 10 takes seconds with a stand alone ECU. The figure is 18 for good reason, the engine idles smoother like this and engine bay heat is greatly reduced too, the good news is distributor people can enjoy the same benefits simply by switching their vac advance unit from the emissions based ported vacuum to a full manifold signal
2. More revealing is the blue circle directly above, this represents the area of the map visited just as you pull away from rest, as you'll see engine speed is still low from 1,000-1,250rpm but the load is high in the 70kPa region. This is the engine working to take the mass of the car from rest so first initiating momentum, if you've ever bump started a car you'll know that first push to get the car rolling is the hardest part of the job. As we can see above the map is showing 27 degrees in this area which is basically the same as a fully advanced distributor at 3,000rpm, but because the engine is only at 1,000-1,250rpm you could never hope to hit anywhere close to 27 degrees at this low engine speed. In my experience these surprisingly high timing numbers at this point in the map its definitely what the engine wants because like this the car pulls away smoother because at this point its most definitely making more torque. The effect is more pronounced that you may assume, the car immediately becomes significantly nicer to drive and maneuver at low speeds
3. When accelerating and under load we can also see the map at 3,000rpm is giving the engine 30 degrees of timing, I point this out because at 3,000rpm a distributor will also be giving in the region of 28-30 degrees depending on your chosen base timing number. Now move to the right and the purple circle shows us the map continues to add 2-3 degrees timing where a distributor would be all done, continue to increase engine speed and we can now see in the green circle the map actually starts to pull timing to bring the number back in line with what you get from a distributor. These timing differences are small but useful, however the truth is this area of higher engine speed under load (accelerating to peak power) is where the distributorless ignition system doesn't really give much advantage. This is why people shouldn't expect an increase in peak power when they move to an aftermarket stand alone ECU with 3D ignition timing control, basically as long as you give the engine 30 degrees of timing and an air fuel ratio of 12.8:1 it will always give the same peak number, the standard 14CUX and distributor can do that just fine, indeed you can easily do it with a carb and a distributor too
4. Now move your gaze down the table to the yellow circle, this is the area of light load cruise where engine load is low and engine speed is highish at 2,850 - 3,000rpm, under these conditions your Chimaera in 5th gear will have a road speed between 76-80mph which is certainly my typical motorway cruising speed. Under these conditions an internal combustion engine will happily run lean of stoich (14.7:1), typically a target of 16.0:1 or even leaner can be achieved on a Chimaera with no ill effects (stumble). However leaner mixtures are harder to strike (initiate the burn) and their burn speed is much slower too, so it stands to reason you need to light the fire earlier. In the above example we can see the map (yellow circle) is delivering a whopping 47 degrees at 76-80mph 5th gear motorway cruising work which delivers optimal fuel economy when burning the lean 16.5:1 AFR closed loop fueling is shooting for at this point. Compare this with a distributor that even with a working connected vacuum advance system will only at best give 30 degrees mechanical advance plus 10 degrees of vacuum advance = 40 degrees so a full 7 degrees short of optimal.
Now compare the optimal 47 degrees figure with a distributor that's had it's vacuum advance disconnected, like that the distributor is only ever going to give you the 30 degrees mechanical advance it has to offer, so a massive fuel economy reducing 17 degrees less timing than optimal. A vacuum advance unit can only ever give benefits, disconnecting it is plain daft and most definitely will not magically give you more horsepower because under load there is no vacuum so it does nothing, when accelerating you're left with the exact same 30 degrees from the distributor with or without the vacuum advance connected. But at cruise at least you get 40 degrees of timing which while still 7 degrees off of the optimal you can achieve from a distributorless ignition system is still massively better than the 30 degrees at cruise a distributor would give you if you foolishly disconnect your vac advance unit
While you may not be able to achieve these numbers with your distributor the following map will hopefully help distributor people see why it would be utter madness to disconnect their vacuum advance unit (see point 4 below for more detail), it is after all the nearest thing you have to 3D ignition timing control.
Studying the above map there are some interesting takeaways:
1. The blue cell shows us where the engine idles.... at 1,000rpm at a load of 45kPa combustion is being initiated at 18 degrees of crankshaft rotation before top dead centre, compare this with the emissions based 10 degrees a standard distributor Chimaera would be running on ported vacuum. Trust me if 10 degrees was best we would see 10 in that blue cell because changing it from 18 to 10 takes seconds with a stand alone ECU. The figure is 18 for good reason, the engine idles smoother like this and engine bay heat is greatly reduced too, the good news is distributor people can enjoy the same benefits simply by switching their vac advance unit from the emissions based ported vacuum to a full manifold signal
2. More revealing is the blue circle directly above, this represents the area of the map visited just as you pull away from rest, as you'll see engine speed is still low from 1,000-1,250rpm but the load is high in the 70kPa region. This is the engine working to take the mass of the car from rest so first initiating momentum, if you've ever bump started a car you'll know that first push to get the car rolling is the hardest part of the job. As we can see above the map is showing 27 degrees in this area which is basically the same as a fully advanced distributor at 3,000rpm, but because the engine is only at 1,000-1,250rpm you could never hope to hit anywhere close to 27 degrees at this low engine speed. In my experience these surprisingly high timing numbers at this point in the map its definitely what the engine wants because like this the car pulls away smoother because at this point its most definitely making more torque. The effect is more pronounced that you may assume, the car immediately becomes significantly nicer to drive and maneuver at low speeds
3. When accelerating and under load we can also see the map at 3,000rpm is giving the engine 30 degrees of timing, I point this out because at 3,000rpm a distributor will also be giving in the region of 28-30 degrees depending on your chosen base timing number. Now move to the right and the purple circle shows us the map continues to add 2-3 degrees timing where a distributor would be all done, continue to increase engine speed and we can now see in the green circle the map actually starts to pull timing to bring the number back in line with what you get from a distributor. These timing differences are small but useful, however the truth is this area of higher engine speed under load (accelerating to peak power) is where the distributorless ignition system doesn't really give much advantage. This is why people shouldn't expect an increase in peak power when they move to an aftermarket stand alone ECU with 3D ignition timing control, basically as long as you give the engine 30 degrees of timing and an air fuel ratio of 12.8:1 it will always give the same peak number, the standard 14CUX and distributor can do that just fine, indeed you can easily do it with a carb and a distributor too
4. Now move your gaze down the table to the yellow circle, this is the area of light load cruise where engine load is low and engine speed is highish at 2,850 - 3,000rpm, under these conditions your Chimaera in 5th gear will have a road speed between 76-80mph which is certainly my typical motorway cruising speed. Under these conditions an internal combustion engine will happily run lean of stoich (14.7:1), typically a target of 16.0:1 or even leaner can be achieved on a Chimaera with no ill effects (stumble). However leaner mixtures are harder to strike (initiate the burn) and their burn speed is much slower too, so it stands to reason you need to light the fire earlier. In the above example we can see the map (yellow circle) is delivering a whopping 47 degrees at 76-80mph 5th gear motorway cruising work which delivers optimal fuel economy when burning the lean 16.5:1 AFR closed loop fueling is shooting for at this point. Compare this with a distributor that even with a working connected vacuum advance system will only at best give 30 degrees mechanical advance plus 10 degrees of vacuum advance = 40 degrees so a full 7 degrees short of optimal.
Now compare the optimal 47 degrees figure with a distributor that's had it's vacuum advance disconnected, like that the distributor is only ever going to give you the 30 degrees mechanical advance it has to offer, so a massive fuel economy reducing 17 degrees less timing than optimal. A vacuum advance unit can only ever give benefits, disconnecting it is plain daft and most definitely will not magically give you more horsepower because under load there is no vacuum so it does nothing, when accelerating you're left with the exact same 30 degrees from the distributor with or without the vacuum advance connected. But at cruise at least you get 40 degrees of timing which while still 7 degrees off of the optimal you can achieve from a distributorless ignition system is still massively better than the 30 degrees at cruise a distributor would give you if you foolishly disconnect your vac advance unit
Post of the year,,, I know it’s been a slow year but credit where credit is due
Now that’s the facts of the matter.
Did you highlight those numbers up Dave,,, im learning computers right now and presentation tools
I’ve learnt about the basics of aftermarket Ecu via online mappers and understand those numbers as you’d expect, isn’t it fantastic to have the ability to adjust these parameters so easily.
In all fairness you also make a good point that actually you can get close with the dizzy/ vacuum system which is quite impressive really.
When you talk of these numbers it corresponds to the changes I recognise in my car too.
More power where you need it, rock solid AFR, lower temps, fuel economy bar blar
The numbers seen here on aftermarket Ecu will be very close to the numbers you’d see on my screen I’m sure of that.
Now that’s the facts of the matter.
Did you highlight those numbers up Dave,,, im learning computers right now and presentation tools
I’ve learnt about the basics of aftermarket Ecu via online mappers and understand those numbers as you’d expect, isn’t it fantastic to have the ability to adjust these parameters so easily.
In all fairness you also make a good point that actually you can get close with the dizzy/ vacuum system which is quite impressive really.
When you talk of these numbers it corresponds to the changes I recognise in my car too.
More power where you need it, rock solid AFR, lower temps, fuel economy bar blar
The numbers seen here on aftermarket Ecu will be very close to the numbers you’d see on my screen I’m sure of that.
Thanks Alun 
Another point of potential interest is the so called shunting zone where people may be surprised to see the table below shows an average of 28 degrees in this problematic area, this is the same as a fully advanced distributor delivers at 3,000rpm, critically a distributor in the shunting zone is only ever likely to deliver in the order of 15-18 degrees at best.
Some may argue a lower timing number is optimal in this problematic area, they may back this up by arguing a lower timing number can be used to mask drivability issues by forcing the driver to open the throttle to quickly pass through the flat spot area, to be clear this is a sticking plaster solution and is the opposite approach to the correct tuning principle of giving the engine what it genuinely wants!
However, even more important than the timing number itself, and believe me the number is super important, are the transitional changes in timing within the areas where drivability is proving challenging. By this I mean changes in degrees of advance/retard (if any) should be kept to an absolute minimum, big jumps in timing numbers are a sure fired way to achieve snatchy throttle response, flat spots and other generally undesirable drivabiliity traits which leads us neatly back to the subject of ported vs full manifold vacuum on a TVR Chimaera or Griff.
If you study whats really going on with the standard emissions based ported vacuum setup you'll see as the throttle butterfly passes the port and the vacumm advance unit switches over to full vacuum a big spike of 5-6 degrees of timing is instantly added, worse still as you then back off the throttle the system instantly takes it away again. This instant and repetitive addition and subtraction of 5-6 degrees of timing is very bad for drivability indeed and will be felt by the driver as what is universally known in TVR circles as shunting.
For example as the driver cruises his TVR through town in what would normally be the ideal gear (3rd gear) at the ideal urban road speeds (25-28mph), the way a Chimaera is geared means the throttle butterfly is constantly passing back and forth over the port. You don't want to be constantly changing from 3rd to 2nd and back to 3rd again so you simply modulate the car's road speed between 25mph (1,650rpm) and 28mph (1,850rpm) using the throttle and staying in 3rd gear. Unfortunately with the emissions based ported vacuum arrangement driving like this means the engine is suffering constant positive and negative swings in timing of the order of 5-6 degrees, it's no wonder the car starts lurching!
These positive and negative spikes in timing are less obvious in a two tonne Range Rover that has huge rolling momentum due to it's considerable mass and its weighty 4x4 transmission too, most also run an automatic so the torque converter does a fantastic job of absorbing and so disguising the shunting. Put the same engine that suffers the same spikes in timing in a super lightweight TVR with a manual gear box and suddenly your lurching through town in a very annoying way.
There's very little mass in the TVR so rolling inertia is far less than the Range Rover, a manual gearbox and regular clutch is also a direct connection between the engine and rear wheels so if the engine lurches because of big timing swings the car will lurch too. To help solve these positive and negative spikes of 5-6 degrees of timing imposed by the emissions based ported vacuum strategy Chimaera owners should just spend a day with the car setup on full manifild vacuum and see what they think, what they should find when switching to full manifold vacuum is the big swings in timing are greatly reduced resulting in far smoother progress in the infamous shunting zone.
Best of all it's free to implement, no expensive Mark Adams chip or trying to burn your own map which are only fuel influences anyway, what you're doing by switching to full manifold vacuum is influencing the far more important element of ignition timing, you are also controlling the positive and negative 5-6 degrees spikes of timing imposed by the nasty emissions based ported vacuum strategy
Another point of potential interest is the so called shunting zone where people may be surprised to see the table below shows an average of 28 degrees in this problematic area, this is the same as a fully advanced distributor delivers at 3,000rpm, critically a distributor in the shunting zone is only ever likely to deliver in the order of 15-18 degrees at best.
Some may argue a lower timing number is optimal in this problematic area, they may back this up by arguing a lower timing number can be used to mask drivability issues by forcing the driver to open the throttle to quickly pass through the flat spot area, to be clear this is a sticking plaster solution and is the opposite approach to the correct tuning principle of giving the engine what it genuinely wants!
However, even more important than the timing number itself, and believe me the number is super important, are the transitional changes in timing within the areas where drivability is proving challenging. By this I mean changes in degrees of advance/retard (if any) should be kept to an absolute minimum, big jumps in timing numbers are a sure fired way to achieve snatchy throttle response, flat spots and other generally undesirable drivabiliity traits which leads us neatly back to the subject of ported vs full manifold vacuum on a TVR Chimaera or Griff.
If you study whats really going on with the standard emissions based ported vacuum setup you'll see as the throttle butterfly passes the port and the vacumm advance unit switches over to full vacuum a big spike of 5-6 degrees of timing is instantly added, worse still as you then back off the throttle the system instantly takes it away again. This instant and repetitive addition and subtraction of 5-6 degrees of timing is very bad for drivability indeed and will be felt by the driver as what is universally known in TVR circles as shunting.
For example as the driver cruises his TVR through town in what would normally be the ideal gear (3rd gear) at the ideal urban road speeds (25-28mph), the way a Chimaera is geared means the throttle butterfly is constantly passing back and forth over the port. You don't want to be constantly changing from 3rd to 2nd and back to 3rd again so you simply modulate the car's road speed between 25mph (1,650rpm) and 28mph (1,850rpm) using the throttle and staying in 3rd gear. Unfortunately with the emissions based ported vacuum arrangement driving like this means the engine is suffering constant positive and negative swings in timing of the order of 5-6 degrees, it's no wonder the car starts lurching!
These positive and negative spikes in timing are less obvious in a two tonne Range Rover that has huge rolling momentum due to it's considerable mass and its weighty 4x4 transmission too, most also run an automatic so the torque converter does a fantastic job of absorbing and so disguising the shunting. Put the same engine that suffers the same spikes in timing in a super lightweight TVR with a manual gear box and suddenly your lurching through town in a very annoying way.
There's very little mass in the TVR so rolling inertia is far less than the Range Rover, a manual gearbox and regular clutch is also a direct connection between the engine and rear wheels so if the engine lurches because of big timing swings the car will lurch too. To help solve these positive and negative spikes of 5-6 degrees of timing imposed by the emissions based ported vacuum strategy Chimaera owners should just spend a day with the car setup on full manifild vacuum and see what they think, what they should find when switching to full manifold vacuum is the big swings in timing are greatly reduced resulting in far smoother progress in the infamous shunting zone.
Best of all it's free to implement, no expensive Mark Adams chip or trying to burn your own map which are only fuel influences anyway, what you're doing by switching to full manifold vacuum is influencing the far more important element of ignition timing, you are also controlling the positive and negative 5-6 degrees spikes of timing imposed by the nasty emissions based ported vacuum strategy
And all that info for free
It’s took a long time and a million shunt threads to get to the bottom of this it seems, let’s hope for all that try this it works, I suppose it’s important to note
Your not adjusting fuelling when doing this as such.
It’s why this is and always has been something that needs a two or maybe three pronged aproach as in timing/ fuel chip and general engine train health ( which is another ball game )
So by following best practice and known results using allsorts of aftermarket Ecu and by just looking at the average numbers at critical points you can see how these aftermarket systems time and again do the same things to maximise volumetric efficiency/ compression/ fuelling and timing to give best results.
There is a pattern to it. Different engines and set ups need different numbers possibly but all aiming for largely the same thing, bang for buck.
Ecu are very funky things,,, with an important job to do, it can’t be underestimated how much more control it gives to me the average owner, I can plug a laptop in and creat God Save the Queen if I so wished,,,
The timing just off idle is very interesting and is often one of the things mentioned as something you notice when getting the latest type of Ecu, “ you can pull away and manoeuvre the car on tickover or the tiniest amount of throttle, this around town adds upto basically no throttle runs itself just about and you barely need it, saves a lot of fuel it seems to me. Coldstarts mine warms faster or just settles when engine is still very cold externally really quickly so again cold start mix leans off within minutes which all adds up.
Mostly it’s nice knowing the engine draws what it needs and nothing more.
Oil stays cleaner for a bit longer, stuff like that, it’s all signs of the efficiency gains these things are capable of. That and Iridium plugs help ,,,
It’s took a long time and a million shunt threads to get to the bottom of this it seems, let’s hope for all that try this it works, I suppose it’s important to note
Your not adjusting fuelling when doing this as such.
It’s why this is and always has been something that needs a two or maybe three pronged aproach as in timing/ fuel chip and general engine train health ( which is another ball game )
So by following best practice and known results using allsorts of aftermarket Ecu and by just looking at the average numbers at critical points you can see how these aftermarket systems time and again do the same things to maximise volumetric efficiency/ compression/ fuelling and timing to give best results.
There is a pattern to it. Different engines and set ups need different numbers possibly but all aiming for largely the same thing, bang for buck.
Ecu are very funky things,,, with an important job to do, it can’t be underestimated how much more control it gives to me the average owner, I can plug a laptop in and creat God Save the Queen if I so wished,,,
The timing just off idle is very interesting and is often one of the things mentioned as something you notice when getting the latest type of Ecu, “ you can pull away and manoeuvre the car on tickover or the tiniest amount of throttle, this around town adds upto basically no throttle
runs itself just about and you barely need it, saves a lot of fuel it seems to me. Coldstarts mine warms faster or just settles when engine is still very cold externally really quickly so again cold start mix leans off within minutes which all adds up. Mostly it’s nice knowing the engine draws what it needs and nothing more.
Oil stays cleaner for a bit longer, stuff like that, it’s all signs of the efficiency gains these things are capable of. That and Iridium plugs help ,,,
Edited by Classic Chim on Saturday 15th December 12:22
Edited by Classic Chim on Saturday 15th December 12:24
Basically it’s opened up that region between 900/1900 revs that at times would cause the shunt by employing the things mentioned here in this thread and used in after market applications and how you can manipulate your CUX ( for best effect) until mot time in a similar fashion upto a point.
By studying your aftermarket ECU use of AFR and timing you can then look at the CUX with greater understanding of what’s going on and when or where best to use it.
Mappers are moving the goalposts in our favour ,,,, all round
Jeez, jacko is about to have one of the best map his car,,, Joolz,,,,,,,, my 1/4 mile time is seriously gonna get blown away,,,,, see what I mean
serious s
t
By studying your aftermarket ECU use of AFR and timing you can then look at the CUX with greater understanding of what’s going on and when or where best to use it.
Mappers are moving the goalposts in our favour ,,,, all round
Jeez, jacko is about to have one of the best map his car,,, Joolz,,,,,,,, my 1/4 mile time is seriously gonna get blown away,,,,, see what I mean
serious st 
Classic Chim said:
And all that info for free It’s took a long time and a million shunt threads to get to the bottom of this it seems, let’s hope for all that try this it works,
The truth is it's just part of the story, the plenum arrangement we suffer is very much early 1980's fuel injection thinking and doesn't help the situation at all, Land Rover knew this which is why they spent considerable time and development budget creating the Thor separated runner twin plenum arrangement, even though they knew the old Rover V8 engine only had a few years left before it was retired for something far more modern and emissions friendly. It’s took a long time and a million shunt threads to get to the bottom of this it seems, let’s hope for all that try this it works,Of course many have already switched to full manifold vacuum Alun, and here's a selection of their comments and feedback scooped up from this and the many other threads on this subject....
Technoholic said:
Ok, so while I can't bear to read anymore of CoG's essays, his points are valid. So basically connecting up the vac advance can only be positive. The question is do I connect it to the original ported vacuum and risk introducing the shunting again, or do I go for manifold vacuum which seemingly has no downsides except emissions. Thoughts?
Belle427 said:
Test them both and see how it drives, I moved over to full manifold vacuum and it’s all been very positive.
Lower under bonnet/running temperatures and better low speed driveability.
And more feedback from those who took my advice and switched to full manifold vacuum...Lower under bonnet/running temperatures and better low speed driveability.
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)
But for me the best advice comes from Belle427 in this statement.....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)
Belle427 said:
Test them both and see how it drives, I moved over to full manifold vacuum and it’s all been very positive.
Lower under bonnet/running temperatures and better low speed driveability.
It's free, and you won't harm your engine, so what have you got to lose trying if for yourself other than your emissions will go up, and if that bothers you just swap back to ported vacuum at MoT time Lower under bonnet/running temperatures and better low speed driveability.
Out of interest. A little story to show how good a modern ECU unit is and what can be done relatively cheaply.
I took my Skoda vRS to my local village garage that had a sticker in the window advertising remapping. They didn’t do it themselves, they were just an agent.
They connected my ECU via the computer and the Internet to the first party tuner, They cleared the map and uploaded a generic map for the vRS and golf GTi, (same engine) standard engine and hey presto, 40 additional horsepower and 100 foot-pounds of troque.
I understand it can’t be absolutely perfect as you’re not mapping an individual engine but given the astonishing gain which I felt instantly it was a he best £200 that I ever spent! All done within an hour as well.
Technology eh!
PS excellent detailed posts Dave.
I took my Skoda vRS to my local village garage that had a sticker in the window advertising remapping. They didn’t do it themselves, they were just an agent.
They connected my ECU via the computer and the Internet to the first party tuner, They cleared the map and uploaded a generic map for the vRS and golf GTi, (same engine) standard engine and hey presto, 40 additional horsepower and 100 foot-pounds of troque.
I understand it can’t be absolutely perfect as you’re not mapping an individual engine but given the astonishing gain which I felt instantly it was a he best £200 that I ever spent! All done within an hour as well.
Technology eh!
PS excellent detailed posts Dave.
I don't need any more convincing to connect back up the advance (I didn't disconnect it in the first place, I just discovered it's been broken). I just need to do it. Also going manifold vacuum seems to be the way to go.
I was doing some other work on the car today and broke the bracket that holds the carbon canister in place. I rigged something up temporarily using cable ties! but im thinking of getting rid of it, sticking a filter on the breather, and then I'll have the trumpet base hose free. I take it this is the one I can use to obtain manifold vacuum if I go this route?
On the other hand, while I know I need to connect it back up, I've got no motivation to actually open up the distributor, change the vacuum advance, and do all the other associated work just because since I've replaced the cap, rotor and leads, it runs like a different car. It is SO smooth, there is no shunting whatsoever, I can't believe the difference. So, while I completely understand why I SHOULD connect it back up, part of me is tempted to just leave it for the time being, as I plan to go for a proper aftermarket ignition/ecu at some point in the near future, once I've sorted the car out mechanically, so that's why im tempted to just hold off. If it was a 5 minute job then I'd just do it, but on my driveway, it's not.
Unless of course Phazed would give me a hand when I visit!
I was doing some other work on the car today and broke the bracket that holds the carbon canister in place. I rigged something up temporarily using cable ties! but im thinking of getting rid of it, sticking a filter on the breather, and then I'll have the trumpet base hose free. I take it this is the one I can use to obtain manifold vacuum if I go this route?
On the other hand, while I know I need to connect it back up, I've got no motivation to actually open up the distributor, change the vacuum advance, and do all the other associated work just because since I've replaced the cap, rotor and leads, it runs like a different car. It is SO smooth, there is no shunting whatsoever, I can't believe the difference. So, while I completely understand why I SHOULD connect it back up, part of me is tempted to just leave it for the time being, as I plan to go for a proper aftermarket ignition/ecu at some point in the near future, once I've sorted the car out mechanically, so that's why im tempted to just hold off. If it was a 5 minute job then I'd just do it, but on my driveway, it's not.
Unless of course Phazed would give me a hand when I visit!
phazed said:
Out of interest. A little story to show how good a modern ECU unit is and what can be done relatively cheaply.
I took my Skoda vRS to my local village garage that had a sticker in the window advertising remapping. They didn’t do it themselves, they were just an agent.
They connected my ECU via the computer and the Internet to the first party tuner, They cleared the map and uploaded a generic map for the vRS and golf GTi, (same engine) standard engine and hey presto, 40 additional horsepower and 100 foot-pounds of troque.
I understand it can’t be absolutely perfect as you’re not mapping an individual engine but given the astonishing gain which I felt instantly it was a he best £200 that I ever spent! All done within an hour as well.
Technology eh!
PS excellent detailed posts Dave.
It’s certainly an eye opener how quickly and easily modern turbocharged cars can be modified.I took my Skoda vRS to my local village garage that had a sticker in the window advertising remapping. They didn’t do it themselves, they were just an agent.
They connected my ECU via the computer and the Internet to the first party tuner, They cleared the map and uploaded a generic map for the vRS and golf GTi, (same engine) standard engine and hey presto, 40 additional horsepower and 100 foot-pounds of troque.
I understand it can’t be absolutely perfect as you’re not mapping an individual engine but given the astonishing gain which I felt instantly it was a he best £200 that I ever spent! All done within an hour as well.
Technology eh!
PS excellent detailed posts Dave.
Technoholic said:
I don't need any more convincing to connect back up the advance (I didn't disconnect it in the first place, I just discovered it's been broken). I just need to do it. Also going manifold vacuum seems to be the way to go.
I was doing some other work on the car today and broke the bracket that holds the carbon canister in place. I rigged something up temporarily using cable ties! but im thinking of getting rid of it, sticking a filter on the breather, and then I'll have the trumpet base hose free. I take it this is the one I can use to obtain manifold vacuum if I go this route?
On the other hand, while I know I need to connect it back up, I've got no motivation to actually open up the distributor, change the vacuum advance, and do all the other associated work just because since I've replaced the cap, rotor and leads, it runs like a different car. It is SO smooth, there is no shunting whatsoever, I can't believe the difference. So, while I completely understand why I SHOULD connect it back up, part of me is tempted to just leave it for the time being, as I plan to go for a proper aftermarket ignition/ecu at some point in the near future, once I've sorted the car out mechanically, so that's why im tempted to just hold off. If it was a 5 minute job then I'd just do it, but on my driveway, it's not.
Unless of course Phazed would give me a hand when I visit!
If you mark the distributor with tippex or white paint where it sits in the timing cover can you loosen it and rotate it enough to get at it then?I was doing some other work on the car today and broke the bracket that holds the carbon canister in place. I rigged something up temporarily using cable ties! but im thinking of getting rid of it, sticking a filter on the breather, and then I'll have the trumpet base hose free. I take it this is the one I can use to obtain manifold vacuum if I go this route?
On the other hand, while I know I need to connect it back up, I've got no motivation to actually open up the distributor, change the vacuum advance, and do all the other associated work just because since I've replaced the cap, rotor and leads, it runs like a different car. It is SO smooth, there is no shunting whatsoever, I can't believe the difference. So, while I completely understand why I SHOULD connect it back up, part of me is tempted to just leave it for the time being, as I plan to go for a proper aftermarket ignition/ecu at some point in the near future, once I've sorted the car out mechanically, so that's why im tempted to just hold off. If it was a 5 minute job then I'd just do it, but on my driveway, it's not.
Unless of course Phazed would give me a hand when I visit!
It’s quite a simple job if you can access it, leads and cap should just tuck up out of the way.
Belle427 said:
It’s certainly an eye opener how quickly and easily modern turbocharged cars can be modified.
In the days of my SX200 it was a couple of quid for a strong waste gate spring. They still have you by the short and curlies even at £200 for changing a couple of software values just to hold the turbo pressure for a few hundred RPM more.I do totally agree with COG on fact that ported vacuum is a bad thing and idle and low speed is far better with a direct plenum vacuum, but it would be interesting if the shunting point was exactly the same as point as the throttle plate edge passes the vacuum port take of to make the big shifts in timing. Difficult one to measure under load as you can hardly point a strobe at the crank pulley whist driving the car....
Peter, yes Monday or Tuesday are out anyway for me for it would need to be after Christmas now if you’re away. I’m not back to work until the 2nd so hopefully if the weather stays ok we can arrange something between Christmas and the 2nd.
In regards to the vacuum, I’m not questioning anyone’s knowledge and I agree that the butterfly passing over the vacuum port could account for big immediate pressure changes and therefore shunting however surely when these cars were new, people wouldn’t have been complaining about shunting, I can imagine if I test drove a car like mine was before I fixed the issues this week, there’s no way I would have bought it if it was new, so how was this issue a non issue 20+ years ago if ported vacuum was how it came out the factory?
Like I said, CoGs points, and others, make complete sense, and now thinking about it I can’t imagine going for ported vacuum feed, but I’m just wondering how it was back then?
By the way I had a quick drive after changing my headlights and fixing my carbon canister back to the wing with cable ties, just to make sure nothing immediately broke, and I’m still so speechless about how smooth and powerful it now feels since changing the cap and rotor and leads. I was driving in 5th about as low as the revs could go and put my foot down and it just pulled smoothly on and on. It’s fantastic! Now if I could just sort my steering out...
In regards to the vacuum, I’m not questioning anyone’s knowledge and I agree that the butterfly passing over the vacuum port could account for big immediate pressure changes and therefore shunting however surely when these cars were new, people wouldn’t have been complaining about shunting, I can imagine if I test drove a car like mine was before I fixed the issues this week, there’s no way I would have bought it if it was new, so how was this issue a non issue 20+ years ago if ported vacuum was how it came out the factory?
Like I said, CoGs points, and others, make complete sense, and now thinking about it I can’t imagine going for ported vacuum feed, but I’m just wondering how it was back then?
By the way I had a quick drive after changing my headlights and fixing my carbon canister back to the wing with cable ties, just to make sure nothing immediately broke, and I’m still so speechless about how smooth and powerful it now feels since changing the cap and rotor and leads. I was driving in 5th about as low as the revs could go and put my foot down and it just pulled smoothly on and on. It’s fantastic! Now if I could just sort my steering out...
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