Distributer vacuum tube missing...?
Discussion
davep said:
Surely the original design criteria for the Rover V8/Lucas DLM8 EFi distributor set up would have been entirely based on partial manifold vacuum not full manifold vacuum?.
Not true, you can run it either on ported vacuum or full manifold vacuum, have a look at Japanese market MG RV8s and you'll see they run the exact same distributor with the vac advance connected to full manifold vacuum.The Lucas distributor fitted to our cars isn't some sort of special device, it's just a distributor! Switching from the emissions based ported vacuum system will only have an effect at idle, the difficult moment just off idle.... and on small throttle openings where poor drivability is common.
By switching your vacuum advance from the ported vacuum to a full manifold vacuum signal you should find the following:
1. An increase in idle timing of approximately 4-6 degrees
2. A corresponding increase in idle speed, obviously you'll need to correct this by winding in the base idle screw
3. A smoother idle
4. Far lower exhaust manifold temperatures
5. Improved throttle response just off idle
6. Better drivability just off idle and at small throttle openings
7. An elimination of the need to precisely adjust the throttle butterfly air gap which is critical with the ported vacuum system
8. Improved engine behavior during the warm up phase
9. An increase in emissions
Basically there are six clear benefits in moving to a full manifold vacuum signal, against the one negative which is an increase in emissions at idle.
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 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.
Even in the 80's the Rover V8 was considered a very dirty engine, ever stricter emission targets and the typical lack of investment that plagued the British motor industry meant more and more sticking plaster solutions were cobbled onto the engine. All this in a desperate bid to make this dinosaur of an engine clean enough to remain in production, when what they really should have done is start with a clean sheet of paper and design a completely new power plant that would naturally meet the standards.
All these sticking plaster emissions strategies are in conflict with what the engine actually wants, in engineering you never get something for nothing, so while these sticking plaster solutions tend to clean up the engine in one way they also make it run worse in many others.
Example 1. The key issue for the Rover V8 is it's poor breathing, while catalytic converters are very effective at reducing tail pipe emissions they are also very restrictive. So you take an engine that naturally struggles to shift it's exhaust gasses in the first place then restrict the exhaust even more, yes the cats will help the old engine pass ever stricter emissions standards but you end up strangling an already poor breathing design even further.
Example 2. Run the engine at 10 degrees at idle and yes you lower your NOx and HCs figures but this is an engine that prefers to idle at 18 degrees. In order to retain the economy benefits of the vac advance unit but make it ineffective at idle to improve idle emissions you deploy ported vacuum, yes you improve emissions but you also introduce big swings in timing just off idle and introduce all the drivability issues that go with that.
Example 3. Run the engine everywhere at 14.7:1 AFR including idle and again you've reduced your emissions, but while 14.7:1 is stoichiometric it is also not really what an inefficient breathing engine like the Rover V8 wants, especially at idle and during low speed driving where something far richer will give significant improvements in drivability and idle smoothness.
The above are just three examples (there are more) of how the engineers at Land Rover during the 80's and 90's managed to eek a few more years out of an ancient and very dirty old engine using a number of what can only be described as sticking plaster solutions. If you strip away all this sticking plaster emissions junk and go back to how the engineers at Buick intended the engine to be when they designed it in the late 1950's you'll find it'll be way way happier.
1. Remove all three catalytic converters
2. Run more ignition advance at idle, the best way to do this is switch from ported vacuum to full manifold vacuum which offers the additional drivability benefits explained at length previously
3. Burn a richer 14CUX Eprom chip to move away from the inappropriately lean 14.7:1 target (especially at idle)
After that you want to completely go through your ignition system, replace the highly inappropriate and way too cold No 7 shrouded electrode plugs specified by TVR which foul easily, then replace with a set of BPR6ES or better still BPR6EIX iridiums. Avoid Magnecor leads, buy a set of decent leads like MSD Super Conductors, and most importantly wrap the ends to protect them from the TVR manifolds so you can throw the dreadful misfire educing plug extenders in the bin where they belong.
Follow all the above and with a few other simple checks and adjustments like base idle, throttle butterfly air gap, TPS setting ect ect, and you will find your TVR idles and drives like a different car. You may also want to restrict the interference the stepper motor and the rather overly aggressive crankcase breather system has on engine behavior as these two elements are really just big induction leaks, all be them managed ones they are still bad news when you're trying to achieve good drivability, idle quality and generally nice engine manners.
None of the above is especially expensive but it will all make a huge difference, of course with no cats, advanced idle timing, and a richer fuel map you will also need to find yourself an understanding MoT tester who is happy to overlook the emissions element of the test, but once you've found such a reasonable minded guy you'll never look back!
I absolutely guarantee you... 'The more of the sticking plaster emissions improving junk you remove... the better your Rover V8 will run'!
^^^^^^^
Thanks for the detailed response, not much of which applies to my car but you weren't to know that.
For my car, a '92 pre-cat, I've dialled in approx 12 degrees advance at idle by setting the distributor position accordingly and it idles fine using Super Unleaded, what the exact ignition advance figures are for cruising speed I've no idea but probably about 28-30 degrees. I note that a lot of the 'how to vacuum tune' videos recommend readjusting the distributor position for lower idle advance when going from ported to full vacuum, which kind of answers my initial question: can going from partial to full vacuum (without readjusting distributor position) result in advance values that are too high. So at the end of day I'll just stick with ported vacuum as I have 12 degrees at idle anyway. It's an interesting topic though.
BTW I've always believed the main reason the Yanks and Japanese prefer full vacuum advance on their carburated gas guzzlers is due to the relatively low speed limits imposed on their national highways, where at the maximum allowed a car is at a low RPM cruise speed with very little throttle activity. I could be wrong, but cruising a 427 cubic inch big block all day at 55 mph probably makes full vacuum the better option.
In your posts you often make disparaging remarks about the 'dated' and clockwork technology used in our TVRs, which grinds a bit. I for one wouldn't have it any other way. Would you, for instance, buy an 80's Rolex watch and then replace the movement with a quartz one?
Thanks for the detailed response, not much of which applies to my car but you weren't to know that.
For my car, a '92 pre-cat, I've dialled in approx 12 degrees advance at idle by setting the distributor position accordingly and it idles fine using Super Unleaded, what the exact ignition advance figures are for cruising speed I've no idea but probably about 28-30 degrees. I note that a lot of the 'how to vacuum tune' videos recommend readjusting the distributor position for lower idle advance when going from ported to full vacuum, which kind of answers my initial question: can going from partial to full vacuum (without readjusting distributor position) result in advance values that are too high. So at the end of day I'll just stick with ported vacuum as I have 12 degrees at idle anyway. It's an interesting topic though.
BTW I've always believed the main reason the Yanks and Japanese prefer full vacuum advance on their carburated gas guzzlers is due to the relatively low speed limits imposed on their national highways, where at the maximum allowed a car is at a low RPM cruise speed with very little throttle activity. I could be wrong, but cruising a 427 cubic inch big block all day at 55 mph probably makes full vacuum the better option.
In your posts you often make disparaging remarks about the 'dated' and clockwork technology used in our TVRs, which grinds a bit. I for one wouldn't have it any other way. Would you, for instance, buy an 80's Rolex watch and then replace the movement with a quartz one?
davep said:
In your posts you often make disparaging remarks about the 'dated' and clockwork technology used in our TVRs, which grinds a bit. I for one wouldn't have it any other way. Would you, for instance, buy an 80's Rolex watch and then replace the movement with a quartz one?
It is clockwork and if something better was available they would use it because it’s more reliable and achieves a better result. Why suffer something inferior? Put a mapped ignition system in and simply keep your clockwork dizzy on the shelf and sell on with the car - I bet they never fit it.BTW I have a pulsar P2 - it doesn’t keep accurate time. If it stops working i will be replacing it with a modern reengineered guts that retains the original looks but had a modern chip inside it.
Edited by eliot on Sunday 15th July 14:38
I went for a great drive early this morning, a blast around the lanes and B roads of deepest Kent, all I can say is vacuum tube or not, I've stopped caring, the car drove so well I forgot about all this, also, no idling problems, no shunting, it's running really well, touch wood!
And the acceleration is superb, blistering. I'll replace the hose and see if it changes anything, but honestly, it's difficult to imagine it being any better than it is, plus I don't need it to be any better, it's performing more than well enough to satisfy my driving skills.
And the acceleration is superb, blistering. I'll replace the hose and see if it changes anything, but honestly, it's difficult to imagine it being any better than it is, plus I don't need it to be any better, it's performing more than well enough to satisfy my driving skills.
eliot said:
davep said:
In your posts you often make disparaging remarks about the 'dated' and clockwork technology used in our TVRs, which grinds a bit. I for one wouldn't have it any other way. Would you, for instance, buy an 80's Rolex watch and then replace the movement with a quartz one?
It is clockwork and if something better was available they would use it because it’s more reliable and achieves a better result. Why suffer something inferior? Put a mapped ignition system in and simply keep your clockwork dizzy on the shelf and sell on with the car - I bet they never fit it.BTW I have a pulsar P2 - it doesn’t keep accurate time. If it stops working i will be replacing it with a modern reengineered guts that retains the original looks but had a modern chip inside it.
Sticking with the wristwatch analogy I've owned both high end expensive mechanical/automatic watches and far cheaper but good quality Japanese quartz watches, my quartz watches always kept better time. The uncomfortable truth the Swiss watch industry doesn't want you to know is a good quartz movement watch will always be more accurate than a timepiece with even the best mechanical/automatic movement.
I'm afraid to reveal electronics are always going to be more accurate than mechanics, this is why your TVR is fitted with an ECU rather than a carburetor, sadly the Lucas system only controls fuel and idle duties. Basically what TVR gave the Chimaera and Griffiths was a half way house system that was already very out of date in the 90's when they were making our cars, all contemporary vehicles at the time ran some sort of ECU managed distributorless ignition system (DIS) because quite simply it's immeasurably superior to a distributor.
If you wanted to fit a better system to your TVR Griff or Chimaera the first thing you'd do is throw the clockwork distributor away and hand ignition timing management over to an ECU, if you cant afford this for heavens sake don't disconnect your vacuum advance system because that's taking an already ancient and compromised ignition system and removing the very thing that actually makes it a little closer to an adaptive 3D ignition map.
Here's a typical distributor curve for a small block Chevy V8...
And by contrast here's my Canems 3D map...
As we can see the images clearly demonstrate the distributor offers a very crude one dimensional curve, while the Canems system delivers what for obvious reasons we call a 3 dimensional ignition map.
Actually if you could show the effects of the vacuum advance on the very simple one dimensional distributor curve it would look a little more like my 3D Canems ignition map, however.... disconnect the vacuum advance as some seem to be advocating here and you're immediately back to that very basic 1D curve which clearly would be a massive backward step
I'm sorry people feel I'm being disparaging about distributor ignitions systems, please be reassured I'm not trying to offend I'm merely saying it as it is, if I said your laptop is infinitely better than a typewriter that's not me having a go at typewriters... its just a statement of fact!
Very interesting thread, which I have just read from start to finish.
For the record, I have a hand built British watch, with a swiss movement in it (serial number 103, so truly bespoke). It is a fantastic piece of character, although it does a loose a few seconds a day. I wear it maybe two or three times a month when I feel like it, and I love it. Today, like most days, there is a digital display on my wrist which is very accurate and gives me loads of other data I don't really need, but is completely devoid of character.
I also have a pre-cat Griff. For the record, the vacuum pipe is attached. I drive it two or three times a month, when I feel like it, and love it. My sensible every day car is better in every respect. It is faster, more economical, handles better, more comfy, has less emissions etc, but is completely devoid of character.
Even by pre-cat standards, this is an early Griff, and I believe it to be one of the first after the motor show cars.
I have just done a chassis job, and before hand I gave a lot of thought to what I wanted to achieve.
I have actually kept it as original and standard as possible. Even though, I could have "improved" it along the way at minimal extra cost.
I agree that binning the distributor and having a more modern engine management system would be a huge improvement. Where do you draw the line? Why stick with a 4.0? Why not a 4.6 or 5.0 and add forced induction? Actually, why not an LS engine? The sportmotive chassis would be an improvement as would Nitrons all round. Actually, lets throw it away and just buy a porker GT3, Jag F type or Aston V8 Vantage.
After thinking about this for a long time, I decided to keep the Griff as original as possible. I love it in the same way as I love my watch. However, I can fully see and understand why people do improve and modify them. Everyone has a different set of priorities and a different budget. It is great that so many owners love their cars, and enjoy them, whether as standard, or highly modified.
For the record, I have a hand built British watch, with a swiss movement in it (serial number 103, so truly bespoke). It is a fantastic piece of character, although it does a loose a few seconds a day. I wear it maybe two or three times a month when I feel like it, and I love it. Today, like most days, there is a digital display on my wrist which is very accurate and gives me loads of other data I don't really need, but is completely devoid of character.
I also have a pre-cat Griff. For the record, the vacuum pipe is attached. I drive it two or three times a month, when I feel like it, and love it. My sensible every day car is better in every respect. It is faster, more economical, handles better, more comfy, has less emissions etc, but is completely devoid of character.
Even by pre-cat standards, this is an early Griff, and I believe it to be one of the first after the motor show cars.
I have just done a chassis job, and before hand I gave a lot of thought to what I wanted to achieve.
I have actually kept it as original and standard as possible. Even though, I could have "improved" it along the way at minimal extra cost.
I agree that binning the distributor and having a more modern engine management system would be a huge improvement. Where do you draw the line? Why stick with a 4.0? Why not a 4.6 or 5.0 and add forced induction? Actually, why not an LS engine? The sportmotive chassis would be an improvement as would Nitrons all round. Actually, lets throw it away and just buy a porker GT3, Jag F type or Aston V8 Vantage.
After thinking about this for a long time, I decided to keep the Griff as original as possible. I love it in the same way as I love my watch. However, I can fully see and understand why people do improve and modify them. Everyone has a different set of priorities and a different budget. It is great that so many owners love their cars, and enjoy them, whether as standard, or highly modified.
Edited by BIG DUNC on Sunday 15th July 19:02
[quote=ChimpOnGas]People should know the pulsing vacuum problem only really exists when you run a ported vacuum signal to the vacuum advance unit, and ported vacuum only exists to run retarded timing at idle to reduce emissions. Switch back to old skool manifold vacuum and the signal is way more stable which means far more stable ignition timing under certain conditions, and more stable timing is always going to translate to a far smoother drive.
When ported vacuum was developed in the States in the early 1970's the pulsing vacuum signal to the vacuum advance capsule was a real problem, as the throttle butterfly passes over the port there's a rapid shift from zero vacuum to strong vacuum which caused a big spike in timing as the vac advance unit tugs on the base plate in the distributor, engineers needed to find a solution!
In the above image I have identified the problem area with a red circle, now imagine what's going to happen as the throttle butterfly passes back and forth over the circled ported vacuum port or worse still is sat right on it as you hold a fixed throttle position when driving at small throttle openings. If you want to see the effects for yourself just 'T' in a vacuum gauge to the ported vacuum advance hose and go for a drive in the shunting zone, watch the needle twitch frantically, now imagine each twitch of that needle will equate to timing violently added and subtracted which is a terrible situation for smooth engine operation.
Unfortunately for owners of Chimaeras and Griffs it does seem that cruising through town around 1,700 - 1,800rpm in 3rd gear corresponds perfectly with the throttle butterfly being right on that ported vacuum point, worse still this is actually right where you want to hold the engine as you trickle through urban environments. The way the car is geared means 3rd gear at 1,700 - 1,800rpm is 25mph which is the exact speed you tend to drive at when following super smooth driving modern cars through urban environments. Everyone else is gliding along between 20-25mph in complete serenity while you are following and lurching along in your TVR just praying for the moment these slow coaches will get out of your way so you can open the car up and smooth things out.
The American designers that came up with the emissions reducing ported vacuum idea needed to come up with a solution to these big on/off swings in ignition timing as the throttle butterfly passes the port, or worse still is sat right on it as you hold a small throttle opening which as already covered is typically in a Chim/Griff when driving through town. The solution came in the form of a vacuum delay valve, this little device acted as a pneumatic damper smoothing out those big spikes in timing, Land Rover also adopted this idea in the form of LR Part No: ERC6997
This is quite a rare part now and some will charge you as much as £56 plus postage for this little plastic device, which is absolutely insane
https://www.johncraddockltd.co.uk/series/series-3/...
You will often see ERC6997 fitted to early Griffs & Chimaeras but it seems fairly early on TVR deemed it unnecessary (or too expensive) so they stopped adding it around early 1995. Vacuum delay valves were fitted to pretty much every Yank V8 during the 70's & 80's when ported vacuum became common place so they definitely work and they were definitely needed, but they are only needed if you run ported vacuum!
If you are going to persevere with ported vacuum you really need that vacuum delay valve, but the truth is it's yet another one of those sticking plaster fixes that only exists because designers were trying to reduce idle emissions using what I consider to be the nasty ported vacuum strategy. If you want to fit a cheaper vacuum delay valve than the stupid money being asked for a genuine ERC6997 then FSE make a universal one (Part No: APV001) that for just £20 should do the same job:
https://www.ebay.co.uk/itm/FSE-VACUUM-ADVANCE-ANTI...
There's no question that running a ported vacuum signal to the vacuum advance unit helps lower idle emissions, but it comes with so many other issues if you can find a sympathetic MoT tester who's happy to overlook the emissions element of the test I'd strongly recommend people go back to the good old and far more stable manifold vacuum signal.
Running manifold vacuum you will not need that vacuum delay valve TVR never should have stopped fitting, you will also enjoy the following additional benefits:
1. A smoother idle
2. Far lower exhaust manifold temperatures
3. Improved throttle response just off idle
4. Better drivability just off idle and at small throttle openings
5. An elimination of the need to precisely adjust the throttle butterfly air gap which is critical with the ported vacuum system
6. Improved engine behavior during the warm up phase
That's six clear benefits and the only negative is your emissions at idle will go up, which I'd suggest most of us TVR enthusiasts will be happy to trade for a car that drives so much smoother and runs significantly cooler exhaust manifolds. Or as some have found you could always disconnect the vacuum advance unit altogether, this will definitely smooth the engine out at small throttle openings because you've basically completely eliminated all the nasty issues that come with ported vacuum.
But why disconnect it when you could get all the same improvements and a lot more besides by simply switching from ported vacuum to a nice strong and stable full manifold signal? With manifold vacuum the car will be way more economical than with a disconnected vac advance and it'll run better too.
When ported vacuum was developed in the States in the early 1970's the pulsing vacuum signal to the vacuum advance capsule was a real problem, as the throttle butterfly passes over the port there's a rapid shift from zero vacuum to strong vacuum which caused a big spike in timing as the vac advance unit tugs on the base plate in the distributor, engineers needed to find a solution!
In the above image I have identified the problem area with a red circle, now imagine what's going to happen as the throttle butterfly passes back and forth over the circled ported vacuum port or worse still is sat right on it as you hold a fixed throttle position when driving at small throttle openings. If you want to see the effects for yourself just 'T' in a vacuum gauge to the ported vacuum advance hose and go for a drive in the shunting zone, watch the needle twitch frantically, now imagine each twitch of that needle will equate to timing violently added and subtracted which is a terrible situation for smooth engine operation.
Unfortunately for owners of Chimaeras and Griffs it does seem that cruising through town around 1,700 - 1,800rpm in 3rd gear corresponds perfectly with the throttle butterfly being right on that ported vacuum point, worse still this is actually right where you want to hold the engine as you trickle through urban environments. The way the car is geared means 3rd gear at 1,700 - 1,800rpm is 25mph which is the exact speed you tend to drive at when following super smooth driving modern cars through urban environments. Everyone else is gliding along between 20-25mph in complete serenity while you are following and lurching along in your TVR just praying for the moment these slow coaches will get out of your way so you can open the car up and smooth things out.
The American designers that came up with the emissions reducing ported vacuum idea needed to come up with a solution to these big on/off swings in ignition timing as the throttle butterfly passes the port, or worse still is sat right on it as you hold a small throttle opening which as already covered is typically in a Chim/Griff when driving through town. The solution came in the form of a vacuum delay valve, this little device acted as a pneumatic damper smoothing out those big spikes in timing, Land Rover also adopted this idea in the form of LR Part No: ERC6997
This is quite a rare part now and some will charge you as much as £56 plus postage for this little plastic device, which is absolutely insane
https://www.johncraddockltd.co.uk/series/series-3/...
You will often see ERC6997 fitted to early Griffs & Chimaeras but it seems fairly early on TVR deemed it unnecessary (or too expensive) so they stopped adding it around early 1995. Vacuum delay valves were fitted to pretty much every Yank V8 during the 70's & 80's when ported vacuum became common place so they definitely work and they were definitely needed, but they are only needed if you run ported vacuum!
If you are going to persevere with ported vacuum you really need that vacuum delay valve, but the truth is it's yet another one of those sticking plaster fixes that only exists because designers were trying to reduce idle emissions using what I consider to be the nasty ported vacuum strategy. If you want to fit a cheaper vacuum delay valve than the stupid money being asked for a genuine ERC6997 then FSE make a universal one (Part No: APV001) that for just £20 should do the same job:
https://www.ebay.co.uk/itm/FSE-VACUUM-ADVANCE-ANTI...
There's no question that running a ported vacuum signal to the vacuum advance unit helps lower idle emissions, but it comes with so many other issues if you can find a sympathetic MoT tester who's happy to overlook the emissions element of the test I'd strongly recommend people go back to the good old and far more stable manifold vacuum signal.
Running manifold vacuum you will not need that vacuum delay valve TVR never should have stopped fitting, you will also enjoy the following additional benefits:
1. A smoother idle
2. Far lower exhaust manifold temperatures
3. Improved throttle response just off idle
4. Better drivability just off idle and at small throttle openings
5. An elimination of the need to precisely adjust the throttle butterfly air gap which is critical with the ported vacuum system
6. Improved engine behavior during the warm up phase
That's six clear benefits and the only negative is your emissions at idle will go up, which I'd suggest most of us TVR enthusiasts will be happy to trade for a car that drives so much smoother and runs significantly cooler exhaust manifolds. Or as some have found you could always disconnect the vacuum advance unit altogether, this will definitely smooth the engine out at small throttle openings because you've basically completely eliminated all the nasty issues that come with ported vacuum.
But why disconnect it when you could get all the same improvements and a lot more besides by simply switching from ported vacuum to a nice strong and stable full manifold signal? With manifold vacuum the car will be way more economical than with a disconnected vac advance and it'll run better too.
I've spoken to a few parts dealers, TVRCC people, and the dealer that sold me the car. Without exception mechanics dealers and parts suppliers have told me to leave the hose disconnected, I've tried to buy one and they won't sell me one saying "why? The only benefits are a dubious 2/3% fuel gain at cruising speeds, and it won't do any harm leaving it off"
On my last Chimaera, in 2016, replacing the broken one at a service didn't seem to affect the driving of it at all. As explained at length, it affects fuel consumption though. Since yours is blanked off, it's like having one not working. They aren't expensive to get though:
https://tvr-parts.com/tvr-parts/part-details/tvr-e...
https://tvr-parts.com/tvr-parts/part-details/tvr-e...
ianwayne said:
On my last Chimaera, in 2016, replacing the broken one at a service didn't seem to affect the driving of it at all. As explained at length, it affects fuel consumption though. Since yours is blanked off, it's like having one not working. They aren't expensive to get though:
https://tvr-parts.com/tvr-parts/part-details/tvr-e...
The advance unit is there, it's just the hose that's been disconnected, and the https://tvr-parts.com/tvr-parts/part-details/tvr-e...
connections on the manifold and diaphragm have been blanked off with sealed rubber tubing.
With regard to using full vacuum on a Lucas 35DLM8 distributor advance unit originally designed for use with ported vacuum have a read of this:
https://www.britishvacuumunit.com/ported-vacuum.ht...
https://www.britishvacuumunit.com/ported-vacuum.ht...
griff59 said:
I've spoken to a few parts dealers, TVRCC people, and the dealer that sold me the car. Without exception mechanics dealers and parts suppliers have told me to leave the hose disconnected, I've tried to buy one and they won't sell me one saying "why? The only benefits are a dubious 2/3% fuel gain at cruising speeds, and it won't do any harm leaving it off"
"The only benefits are a dubious 2/3% fuel gain at cruising speeds"
Dubious!!! I've never heard of anything so ridiculous, ask these vac advance disconnecting fools where they're getting their facts from, better still ask them to clearly explain their theory in detail, if they can present evidence even half as comprehensive as mine I'll eat my hat.
A vacuum advance capsule is ancient but extremely well proven technology, its been fitted to almost every single distributor since the late 1940's which is millions and millions and millions of distributors by the way, if it didn't work do you really think that would be the case
If the argument is RV8 TVRs are such high performance vehicles that they demand the vacuum advance must be disconnected I'm here to burst that bubble too, RV8's fitted to TVRs aren't really an engine in a high state of tune and and there's no real performance benefit in removing a vacuum advance anyway, so I'm super keen to hear exactly why these so called experts are recommending it.
Try not to fall into the trap of always trusting the advice of someone just because he's got a workshop or parts store with TVR over the door and because they've got a shiny website, always challenge them to prove their argument in the way I've shown in this post. When you do challenge I guarantee you they'll stumble and struggle to give you a proper evidence supported and credible argument for disconnecting the vacuum advance.
I'm going to assume you couldn't be bothered to read what I've presented here of you just haven't been able to understand it, re-read what I've written, then cross check my carefully well presented and evidenced information with reliable sources. Finally ask yourself if the people telling you to disconnect your vacuum advance are providing you with an equally credible argument for disconnecting the vac advance or if they are just spinning you a load of old BS based on old wives tales and misinformation
Chimp is 100% right here.
I took the time to study vacuum advance on RV8's, ported, and unported. My previous car was a Seight with a 4.3 V8 and huge edelbrock carbs and I spent a lot of time getting it right, most of that time was reading and learning! I am far from an expert. Refitting mine (was blanked off, with no pipe) gave me a significant economy boost overall, and was motivated partly by trying to reduce underbonnet temps, which it helped with.. though by how much I don't know as I also wrapped my manifolds and vented my bonnet.
The vacuum advance does exactly as described by ChimpOnGas.
I imagine the reason that mechanics all say "leave it off" is because
a) it's what they've been told by someone else
b) "why bother for a few mpg in a car that noone really cares about its mpg"
c) just another thing to go wrong.
It really should be there.
A note about the "clockwork". Dizzy's really are crude and do not compare to 3d mapping with an EDIS system. Comparing this to a watch is not a comparison that makes any sense.
I converted mine from a dizzy to a megajolt EDIS system and it worked a treat (in the Seight). However.... it adds a LOT more points of failure. Lots of wiring that if even one connection is not perfect, can cause head scratching problems down the line. Don't I know about it! (grrrr!). One poor soldered wire joint took a couple of weeks to diagnose and locate, the, after a while, I went from a 6.5k clean revving tuned v8 to an engine that would cut after 5.5k - changed the EDIS module, resoldered everything - never got to the bottom of it and often thought about putting the dizzy back on! :-)
I took the time to study vacuum advance on RV8's, ported, and unported. My previous car was a Seight with a 4.3 V8 and huge edelbrock carbs and I spent a lot of time getting it right, most of that time was reading and learning! I am far from an expert. Refitting mine (was blanked off, with no pipe) gave me a significant economy boost overall, and was motivated partly by trying to reduce underbonnet temps, which it helped with.. though by how much I don't know as I also wrapped my manifolds and vented my bonnet.
The vacuum advance does exactly as described by ChimpOnGas.
I imagine the reason that mechanics all say "leave it off" is because
a) it's what they've been told by someone else
b) "why bother for a few mpg in a car that noone really cares about its mpg"
c) just another thing to go wrong.
It really should be there.
A note about the "clockwork". Dizzy's really are crude and do not compare to 3d mapping with an EDIS system. Comparing this to a watch is not a comparison that makes any sense.
I converted mine from a dizzy to a megajolt EDIS system and it worked a treat (in the Seight). However.... it adds a LOT more points of failure. Lots of wiring that if even one connection is not perfect, can cause head scratching problems down the line. Don't I know about it! (grrrr!). One poor soldered wire joint took a couple of weeks to diagnose and locate, the, after a while, I went from a 6.5k clean revving tuned v8 to an engine that would cut after 5.5k - changed the EDIS module, resoldered everything - never got to the bottom of it and often thought about putting the dizzy back on! :-)
Good post from RogerDoger there 
The Robert Medynski website is also a good general source of Lucas distributor information but it really relates to the models fitted to Triumphs and MGs. The Rover V8 is closer related to an American V8 as it is an American V8, as such it should be treated as one!
If you go back to the 50's & 60's when no one cared about emissions, all big American V8s ran full manifold vacuum because they always run better like that. Back in the day no Yank would ever dream of using ported vacuum which only really arrived as an ignition strategy in the very late 1960s/early 70's as a way of reducing idle emissions.
A good bit of information on Rob's website is at the bottom of this page....
https://www.britishvacuumunit.com/our-products.htm...
Where he clearly states......
Non-vacuum advance performance distributors! ..... Should only be installed when involved in high performance racing or under constant wide open conditions. Not good for street use. Anyone replacing a OE vacuum advance distributor with a performance mechanical advance distributor doesn't understand the operation of the vacuum advance unit. The original OE distributor with a vacuum advance unit, enhances cooling, engine efficiency, throttle response,and fuel economy.
On the subject of running a vac advance capsule on full manifold vacuum that was intended to run ported vacuum, the truth is you can make the switch without worry or issue. Rover themselves did it on Japanese MG RV8s and lot's of Chimaera owners have done it already will excellent results, if you think about it the only difference is the vac advance under full manifold vacuum works from idle up where the ported system will apply the exact same levels of advance at engine speeds a little higher. Both manifold vacuum and ported vacuum are in fact manifold vacuum systems, it's just ported vacuum only switches to manifold vacuum when the throttle butterfly passes the port.
By approximately 2,000rpm there's no difference between the two systems whatsoever, all running full manifold vacuum gives is a more stable vacuum signal from idle to 2,000rpm. I say all, but actually this small difference has a big positive impact on drivability just off idle.... and especially around 1,700-1,800rpm on our cars
And RogerDoger is right again when he talks about the benefits of distributors being simple, a well set up RV8 running a fresh unworn distributor with full manifold vacuum can give a very smooth drive indeed. As such you don't really need a fancy engine management system, it will most definitely give you the last word in efficiency but there's still a lot to be said for simplicity. Saying that I would never go back to a distributor, my Canems Dual Fuel ECU gives me so much control over fuel and ignition it opens up a world of opportunity, not least the ability to deliver the perfect combustion on LPG which turns my 4.0 litre V8 Chimaera into a 48mpg (petrol cost equivalent) TVR
Try doing this with a distributor....
No chance!
The Robert Medynski website is also a good general source of Lucas distributor information but it really relates to the models fitted to Triumphs and MGs. The Rover V8 is closer related to an American V8 as it is an American V8, as such it should be treated as one!
If you go back to the 50's & 60's when no one cared about emissions, all big American V8s ran full manifold vacuum because they always run better like that. Back in the day no Yank would ever dream of using ported vacuum which only really arrived as an ignition strategy in the very late 1960s/early 70's as a way of reducing idle emissions.
A good bit of information on Rob's website is at the bottom of this page....
https://www.britishvacuumunit.com/our-products.htm...
Where he clearly states......
Non-vacuum advance performance distributors! ..... Should only be installed when involved in high performance racing or under constant wide open conditions. Not good for street use. Anyone replacing a OE vacuum advance distributor with a performance mechanical advance distributor doesn't understand the operation of the vacuum advance unit. The original OE distributor with a vacuum advance unit, enhances cooling, engine efficiency, throttle response,and fuel economy.
On the subject of running a vac advance capsule on full manifold vacuum that was intended to run ported vacuum, the truth is you can make the switch without worry or issue. Rover themselves did it on Japanese MG RV8s and lot's of Chimaera owners have done it already will excellent results, if you think about it the only difference is the vac advance under full manifold vacuum works from idle up where the ported system will apply the exact same levels of advance at engine speeds a little higher. Both manifold vacuum and ported vacuum are in fact manifold vacuum systems, it's just ported vacuum only switches to manifold vacuum when the throttle butterfly passes the port.
By approximately 2,000rpm there's no difference between the two systems whatsoever, all running full manifold vacuum gives is a more stable vacuum signal from idle to 2,000rpm. I say all, but actually this small difference has a big positive impact on drivability just off idle.... and especially around 1,700-1,800rpm on our cars
And RogerDoger is right again when he talks about the benefits of distributors being simple, a well set up RV8 running a fresh unworn distributor with full manifold vacuum can give a very smooth drive indeed. As such you don't really need a fancy engine management system, it will most definitely give you the last word in efficiency but there's still a lot to be said for simplicity. Saying that I would never go back to a distributor, my Canems Dual Fuel ECU gives me so much control over fuel and ignition it opens up a world of opportunity, not least the ability to deliver the perfect combustion on LPG which turns my 4.0 litre V8 Chimaera into a 48mpg (petrol cost equivalent) TVR
Try doing this with a distributor....
No chance!
After picking up on previous threads by CoG on ported v full vac and digesting the reasoning, I've set up my standard Griff for full vac by installing a Tee on the fuel regulator vac line.
However, I've not currently switched it over to trial full vac yet cos have a small fuelling issue which want to resolve beforehand but once that's sorted will swap over the blank & the vac line and provide feedback,
However, I've not currently switched it over to trial full vac yet cos have a small fuelling issue which want to resolve beforehand but once that's sorted will swap over the blank & the vac line and provide feedback,
Its worth reviewing the comments from StuVT (Stuart Knight) 2/3rds down this page...
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Stuart switched from ported to full manifold vacuum back in in February this year and provided a detailed report on the results.
Well worth reading
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Stuart switched from ported to full manifold vacuum back in in February this year and provided a detailed report on the results.
Well worth reading
If you are after a t-piece when swapping from ported to manifold the ex-Jap MG RV8 guys may be able to help, they are advised to go back to ported.
Might be worth letting them know where they're going wrong Chimp!
http://www.mgrv8.com/ownerstips.php
Might be worth letting them know where they're going wrong Chimp!
http://www.mgrv8.com/ownerstips.php
davep said:
If you are after a t-piece when swapping from ported to manifold the ex-Jap MG RV8 guys may be able to help, they are advised to go back to ported.
Might be worth letting them know where they're going wrong Chimp!
http://www.mgrv8.com/ownerstips.php
Telling them where they're going wrong is easy, actually they do It all by themselves, if you read that nonsense you'll soon see these enthusiastic MB RV8 amateurs haven't got a clue, just reading this extract proves it...Might be worth letting them know where they're going wrong Chimp!
http://www.mgrv8.com/ownerstips.php
"It has been found all Ex-Japanese vehicles have their distributor vacuum advance pipes coming from the side of the plenim chamber.
This is seriously wrong as it causes constant vacuum to the distributor which inturn causes the timing to be fully advanced all the time"
No it doesn't, of course the timing isn't fully advanced all the time, the device is called a vacuum advance unit, the clue it is in the name, it needs vacuum to work and an engine doesn't produce meaningful levels of vacuum ALL THE TIME ....
This one statement alone proves the MG RV8 crowd haven't got a clue what they are talking about, but there's more, the guy who scribbled that nonsense goes on to use the term 'Plenim Chamber', what the fek is a 'Plenim Chamber'
. Then to conclusively prove his ignorance he comes up with the nonsense term 'butterfly chamber' which again proves he's never had any formal education in mechanics because 'butterfly chamber' is not a term used by any automotive engineer or mechanic.'Butterfly Chamber' is clearly the MG RV8 author's own made up word and is him getting muddled up between 'Plenum Chamber' and 'Throttle Body' both of which are true automotive terms for recognised components that (along with other elements) make up the induction system on a fuel injected engine.
The statement that full vacuum causes the timing to be fully advanced all the time, the use of the non word Plenim and then the nonsense term 'Butterfly Chamber' all proves Mr Enthusiastic RV8 Amateur doesn't know what he's talking about
In one short paragraph the RV8 website author destroys all credibility he might have by making three obvious and ridiculous gaffs, he then fails to support his theory that manifold vacuum is (in his words) 'seriously wrong' with any credible evidence. Japan as a nation are sticklers for detail, they also have extremely high expectations for the way their cars they drive, with such a large percentage of RV8 production going to Japan do you really think full manifold was 'seriously wrong'? Japanese customers would have soon complained if it gave issues and to be frank Rover wouldn't have done it that way in the first place if it didn't work, and work well.
The truth behind all this is Rover realised they didn't need their Japanese market MG RV8 to hit the same strict emissions targets as European cars, so they took the opportunity to run the cars bound for Japan on a full manifold vacuum signal to the vac advance unit because the knew the engine runs better and cooler that way. In summary ported vacuum only existed on the European cars because the European emissions targets were so much stricter than they were at the time in Japan.
ChimpOnGas said:
"The only benefits are a dubious 2/3% fuel gain at cruising speeds"
Dubious!!! I've never heard of anything so ridiculous, ask these vac advance disconnecting fools where they're getting their facts from, better still ask them to clearly explain their theory in detail, if they can present evidence even half as comprehensive as mine I'll eat my hat.
A vacuum advance capsule is ancient but extremely well proven technology, its been fitted to almost every single distributor since the late 1940's which is millions and millions and millions of distributors by the way, if it didn't work do you really think that would be the case
If the argument is RV8 TVRs are such high performance vehicles that they demand the vacuum advance must be disconnected I'm here to burst that bubble too, RV8's fitted to TVRs aren't really an engine in a high state of tune and and there's no real performance benefit in removing a vacuum advance anyway, so I'm super keen to hear exactly why these so called experts are recommending it.
Try not to fall into the trap of always trusting the advice of someone just because he's got a workshop or parts store with TVR over the door and because they've got a shiny website, always challenge them to prove their argument in the way I've shown in this post. When you do challenge I guarantee you they'll stumble and struggle to give you a proper evidence supported and credible argument for disconnecting the vacuum advance.
I'm going to assume you couldn't be bothered to read what I've presented here of you just haven't been able to understand it, re-read what I've written, then cross check my carefully well presented and evidenced information with reliable sources. Finally ask yourself if the people telling you to disconnect your vacuum advance are providing you with an equally credible argument for disconnecting the vac advance or if they are just spinning you a load of old BS based on old wives tales and misinformation
I have read what you've presented but unfortunately most of it goes way above my head. As I said before here, I'm not a mechanic.Dubious!!! I've never heard of anything so ridiculous, ask these vac advance disconnecting fools where they're getting their facts from, better still ask them to clearly explain their theory in detail, if they can present evidence even half as comprehensive as mine I'll eat my hat.
A vacuum advance capsule is ancient but extremely well proven technology, its been fitted to almost every single distributor since the late 1940's which is millions and millions and millions of distributors by the way, if it didn't work do you really think that would be the case
If the argument is RV8 TVRs are such high performance vehicles that they demand the vacuum advance must be disconnected I'm here to burst that bubble too, RV8's fitted to TVRs aren't really an engine in a high state of tune and and there's no real performance benefit in removing a vacuum advance anyway, so I'm super keen to hear exactly why these so called experts are recommending it.
Try not to fall into the trap of always trusting the advice of someone just because he's got a workshop or parts store with TVR over the door and because they've got a shiny website, always challenge them to prove their argument in the way I've shown in this post. When you do challenge I guarantee you they'll stumble and struggle to give you a proper evidence supported and credible argument for disconnecting the vacuum advance.
I'm going to assume you couldn't be bothered to read what I've presented here of you just haven't been able to understand it, re-read what I've written, then cross check my carefully well presented and evidenced information with reliable sources. Finally ask yourself if the people telling you to disconnect your vacuum advance are providing you with an equally credible argument for disconnecting the vac advance or if they are just spinning you a load of old BS based on old wives tales and misinformation
Opinions seem very divided about this vacuum advance issue, and even given the comprehensive factual evidence you've presented the real world differences it makes seem very small, this is obviously the case otherwise we wouldn't be debating about it to this level with no real agreed conclusion.
I ttrust my dealer, and my local TVR mechanic, I have no choice but to trust these people.
I posted my question here expecting more of a majority one way or the other. Your advice and information is well presented and knowledgable, and I appreciate it, but TBQH it's not enough to make me want to do anything about it taking others opinions into consideration as well.
As jobs go it's simple even for me to reinstate the hose, I may well do it, and it will be interesting to see if it makes a worthwhile difference. But I am worried about upsetting it, as it drives/runs so well at the moment.
Edited by griff59 on Tuesday 17th July 08:33
Edited by griff59 on Tuesday 17th July 08:35
It's not blocked off, I've seen a number Jap MG RV8s in the flesh and Rover definitely set these cars up on manifold vacuum.
Why would Rover fit the hose to manifold vacuum then block it off, that makes no sense whatsoever
Seriously.... the flat cap old MG duffers have no idea what they're talking about, all they've done is see the Jap market cars are set up differently to the UK cars, assumed it's wrong, and then put their car on the emissions based ported vacuum strategy with the nasty retarded idle it gives.
I have a fully mappable Canems engine management system I map myself, I can run an exact duplication of ported vacuum emissions improving 10 degrees idle strategy and in seconds switch to the more advanced 18 degrees at idle to replicate what you get with full manifold vacuum.
I have total control and the choice to run either an exact replication of what either ported or manifold vacuum gives with a distributor so I can 100% instantly experiment with what works best then run that setup. If the retarded idle ported strategy worked best believe me I would run that arrangement, but emissions aside I can categorically reassure you running more advance at idle as you would achieve on a distributor with it's vac advance connected to full vacuum is massively better for many many reasons extensively covered in my previous posts.
Running a mappable engine management system and the massive adaptability and flexibility of ignition timing it gives totally proves whats best, no argument!
Why would Rover fit the hose to manifold vacuum then block it off, that makes no sense whatsoever
Seriously.... the flat cap old MG duffers have no idea what they're talking about, all they've done is see the Jap market cars are set up differently to the UK cars, assumed it's wrong, and then put their car on the emissions based ported vacuum strategy with the nasty retarded idle it gives.
I have a fully mappable Canems engine management system I map myself, I can run an exact duplication of ported vacuum emissions improving 10 degrees idle strategy and in seconds switch to the more advanced 18 degrees at idle to replicate what you get with full manifold vacuum.
I have total control and the choice to run either an exact replication of what either ported or manifold vacuum gives with a distributor so I can 100% instantly experiment with what works best then run that setup. If the retarded idle ported strategy worked best believe me I would run that arrangement, but emissions aside I can categorically reassure you running more advance at idle as you would achieve on a distributor with it's vac advance connected to full vacuum is massively better for many many reasons extensively covered in my previous posts.
Running a mappable engine management system and the massive adaptability and flexibility of ignition timing it gives totally proves whats best, no argument!
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