Distributer vacuum tube missing...?
Discussion
carsy said:
chris212 said:
After trying to eliminate the light throttle shunting problem I discovered the one way valve plumbed into the vacuum pipe had failed, and was not allowing any vacuum ( and was the wrong way around!). I've replaced it with just a pipe, and noticed an improvement.
Are you sure the one way valve had failed. You will struggle to suck air through it via ones mouth. This is normal. Its like that to stop any voilent ignition spikes as the throttle passes over it. This would give shunting. It takes a while of constant vacuum for it to work. This way you only get the advance rise when cruising with a constant ish throttle opening which is when you need it rather than when the throttle is constantly being quickly passed over it.
Hope that makes sense its getting late.
If it was a one way valve it would mean detonation promoting amounts of advance under load, the device is not a one way valve, it's just a pneumatic damper!
I am no expert by any means. But when I looked into this, I believe they remove the vacuum pipe on cars that are going to be driven in a very spirited manner, because if it fails and then remains in the fully advanced position it can cause serious engine damage when run with full throttle positions. The advance plate is also sometimes fixed in the non advanced position to prevent it moving.
So if it is being used for track days, racing etc, it would make sense. Conversely not having it connected does not cause damage (from what I read), so it depends on what you use the car for.
So I guess it depends on what TVR's view was when they made some cars if they are missing and the same for any garages who say to remove it.
So if it is being used for track days, racing etc, it would make sense. Conversely not having it connected does not cause damage (from what I read), so it depends on what you use the car for.
So I guess it depends on what TVR's view was when they made some cars if they are missing and the same for any garages who say to remove it.
ahpboxster said:
I am no expert by any means. But when I looked into this, I believe they remove the vacuum pipe on cars that are going to be driven in a very spirited manner, because if it fails and then remains in the fully advanced position it can cause serious engine damage when run with full throttle positions. The advance plate is also sometimes fixed in the non advanced position to prevent it moving.
So if it is being used for track days, racing etc, it would make sense. Conversely not having it connected does not cause damage (from what I read), so it depends on what you use the car for.
So I guess it depends on what TVR's view was when they made some cars if they are missing and the same for any garages who say to remove it.
When a vacuum advance unit fails it's because the diaphragm splits so you get no advance, the base plate mechanism can seize but I've never seen this happen in the advanced position because the springs are always trying to pull it back into the retarded position.So if it is being used for track days, racing etc, it would make sense. Conversely not having it connected does not cause damage (from what I read), so it depends on what you use the car for.
So I guess it depends on what TVR's view was when they made some cars if they are missing and the same for any garages who say to remove it.
We need to move on from the myth that removing the vacuum advance system is some sort of trick performance modification, it's not! Back in the day there were some aftermarket distributors sold only intended for race use that didn't come with a vac advance unit, but only because if you're diving flat out on the track there's little need for one.
In the case of a race only distributor fitting a vac advance just added unnecessary cost, but it most certainly didn't improve performance. The ignorant looked at these race only distributors and decided removing the vacuum advance hose was some sort of performance modification, this is a classic case of someone making assumptions without really understanding how things work.
To be 100% clear there is absolutely no performance gain in disconnecting the vacuum advance unit on any distributor, no matter how the car is driven, period! All you do when you disconnect it is lose fuel economy. However, ported vacuum can give sudden jumps in timing which is why some may have found their car is smoother at small throttle openings with the vacuum advance disconnected, but that's really because the throttle butterfly hasn't been set correctly.
Over in the Chimp cage a few have experimented with switching from ported vacuum to full manifold vacuum, and all are reporting a smoother drive. This is no surprise really when you take the time to understand how the emissions based ported vacuum idea works, the problem with ported vacuum is that moment the throttle butterfly passes over the port at that moment you are instantly switching from atmosphere to full vacuum.
Big jumps in ignition timing are always bad for drivability, and it's especially bad news if you're rapidly adding, subtracting, then adding timing over and over again as you'll get the car in a kangerooing loop for sure. Ever wonder why the only way to pull out of the shunting cycle in to push on the throttle pedal, what you're doing is pushing the knife edge of the throttle butterfly past the port to enter into full vacuum. The drivability issues come about when the butterfly is right on the port, like this it's neither a consistent atmosphere or vacuum signal, it's rapidly switching between the two which is very bad news for smooth progress.
ChimpOnGas said:
<big clip> Some so called TVR Specialists may well have discovered disconnecting the vacuum advance makes the engine a little smoother in some cases, but what they really should have done is studied how the system was designed to work with it connected, then followed the instructions on setting up the engine in the Land Rover factory workshop manual.
ConG, you have clearly studied this subject in depth and I have no axe to grind, however when you say 'Some "so called" TVR specialists' I guess you are including the boy in Blackpool back in the '90s in that group? Reading what you have said suggests they didn't understand the purpose of the vacuum advance and just binned it without proper consideration. Correct? I wouldn’t suggest it is a performance advantage, but the fact a failure would cause serious damage if stuck on advance would explain why it is done. The vacuum diaphragm is only the driver to move the mechanism itself, the mechanism can bind and can need cleaning and lubricating, I have seen it myself and it can stick in advanced position too (not that I have experienced that)
Apparently they (engine conversion people) sometimes spot weld the mechanism to stop it moving on race engines, which would suggest it does happen enough to warrant it. It is not just a cost reason otherwise they would just leave it blanked off.
The opposite is that with it removed no damage will be done, so it makes sense for protection in many ways.
Apparently they (engine conversion people) sometimes spot weld the mechanism to stop it moving on race engines, which would suggest it does happen enough to warrant it. It is not just a cost reason otherwise they would just leave it blanked off.
The opposite is that with it removed no damage will be done, so it makes sense for protection in many ways.
Edited by ahpboxster on Friday 13th July 18:21
Edited by ahpboxster on Friday 13th July 18:25
In the past some race mechanics would lock out the distributor at say 25 degrees, you would never do this on a road car and this practice has been considered old hat in the race car world for years too.
It seems people only want to hear that disconnecting the vacuum advance is some kind of secret performance modification, which I can categorically reassure it is not!
But if you really don't believe me just leave it disconnected, you will feel a victory and the rest of us who know better will get a good laugh at your expense
Or you could just research what I'm saying, after educating yourself properly you'll only ever discover I'm right 
For the record I benefitted from a number of years of formal education in these matters resulting in recognised qualifications, this followed by a period in the trade where I put it all into practice to earn my living.
It seems people only want to hear that disconnecting the vacuum advance is some kind of secret performance modification, which I can categorically reassure it is not!
But if you really don't believe me just leave it disconnected, you will feel a victory and the rest of us who know better will get a good laugh at your expense
Or you could just research what I'm saying, after educating yourself properly you'll only ever discover I'm right For the record I benefitted from a number of years of formal education in these matters resulting in recognised qualifications, this followed by a period in the trade where I put it all into practice to earn my living.
Not sure if that reply is aimed at me as I agreed it was not a performance advantage from the beginning. I wasn’t suggesting you were wrong about why it is there or how it should be used.
So is what I said wrong from the perspective of why it is done for a track/performance day use to avoid potential failure damaging the engine ?. That was the one and only reason i suggested it was done. It is old hat because it’s an old engine.
I run with vacuum advance as I only use mine on the road.
So is what I said wrong from the perspective of why it is done for a track/performance day use to avoid potential failure damaging the engine ?. That was the one and only reason i suggested it was done. It is old hat because it’s an old engine.
I run with vacuum advance as I only use mine on the road.
Edited by ahpboxster on Friday 13th July 19:11
Edited by ahpboxster on Friday 13th July 19:13
Edited by ahpboxster on Friday 13th July 19:23
ChimpOnGas said:
In the past some race mechanics would lock out the distributor at say 25 degrees, you would never do this on a road car and this practice has been considered old hat in the race car world for years too.
It seems people only want to hear that disconnecting the vacuum advance is some kind of secret performance modification, which I can categorically reassure it is not!
But if you really don't believe me just leave it disconnected, you will feel a victory and the rest of us who know better will get a good laugh at your expense Or you could just research what I'm saying, after educating yourself properly you'll only ever discover I'm right
For the record I benefitted from a number of years of formal education in these matters resulting in recognised qualifications, this followed by a period in the trade where I put it all into practice to earn my living.
I don't think there's any need for you to be patronising nor boastful, which your last post certainly came across as. People have asked questions which should tell you that they are interested in your opinion. No one I have met in the TVR community over the last 25 years is interested in point scoring so I doubt there will be anyone laughing behind people's backs - I hope your last post was just an unfortunate way of saying something. Incidentally you've not said if TVR Blackpool were in your group of "so called" specialists who didn't have a clue what they were doing? I was genuinely interested to hear you view. It seems people only want to hear that disconnecting the vacuum advance is some kind of secret performance modification, which I can categorically reassure it is not!
But if you really don't believe me just leave it disconnected, you will feel a victory and the rest of us who know better will get a good laugh at your expense
Or you could just research what I'm saying, after educating yourself properly you'll only ever discover I'm right For the record I benefitted from a number of years of formal education in these matters resulting in recognised qualifications, this followed by a period in the trade where I put it all into practice to earn my living.
RichB said:
don't think there's any need for you to be patronising nor boastful, which your last post certainly came across as. People have asked questions which should tell you that they are interested in your opinion. No one I have met in the TVR community over the last 25 years is interested in point scoring so I doubt there will be anyone laughing behind people's backs - I hope your last post was just an unfortunate way of saying something. Incidentally you've not said if TVR Blackpool were in your group of "so called" specialists who didn't have a clue what they were doing? I was genuinely interested to hear you view.
Just leave it disconnected, it's a brilliant idea supported by loads of evidence 
Honestly, some people just don't want educating, they prefer nonsense and myth over fact!
This post has become laughably pointless
ChimpOnGas said:
RichB said:
don't think there's any need for you to be patronising nor boastful, which your last post certainly came across as. People have asked questions which should tell you that they are interested in your opinion. No one I have met in the TVR community over the last 25 years is interested in point scoring so I doubt there will be anyone laughing behind people's backs - I hope your last post was just an unfortunate way of saying something. Incidentally you've not said if TVR Blackpool were in your group of "so called" specialists who didn't have a clue what they were doing? I was genuinely interested to hear you view.
Just leave it disconnected, it's a brilliant idea supported by loads of evidence Honestly, some people just don't want educating, they prefer nonsense and myth over fact!
This post has become laughably pointless
ChimpOnGas said:
Just leave it disconnected, it's a brilliant idea supported by loads of evidence
Honestly, some people just don't want educating, they prefer nonsense and myth over fact!
This post has become laughably pointless
I'm more confused than ever now, Chimp, you've provided more than enough factual evidence to make me want to to reinstate the vacuum hose, but, like a lot of questions on forums we receive an equal amount of replies stating exactly the opposite, and for every ten people advocating one course of action, there will be another ten advocating another just as viable and convincing course of action. The result unfortunately is confusion, and we are none the wiser.Honestly, some people just don't want educating, they prefer nonsense and myth over fact!
This post has become laughably pointless
I'm a member of the TVR Car Club, and it does seem that the majority of members that I've talked to about this vacuum hose thing it's a matter of "suck it and see" it's no big deal, one way or the other.
I'm sorry if I've opened up a can of worms, and it's pointless to get too concerned about this, there are more important things to think about, like enjoying this weather and our cars, with or without vacuum hoses!
http://www.superchevy.com/how-to/additional-tech/1...
This backs up what C on G said , and explains well.
I am going to switch to manifold vacuum. Ported vacuum seemed to be introduced to Increase engine temp at idle to drop emmisions .
This backs up what C on G said , and explains well.
I am going to switch to manifold vacuum. Ported vacuum seemed to be introduced to Increase engine temp at idle to drop emmisions .
chris212 said:
http://www.superchevy.com/how-to/additional-tech/1...
This backs up what C on G said , and explains well.
I am going to switch to manifold vacuum. Ported vacuum seemed to be introduced to Increase engine temp at idle to drop emmisions .
Glad to see someone is doing their own research, as I said when people take the time to cross check what I'm saying they'll find I'm right, better still the process of researching helps people properly grasp and absorb the reasons why.This backs up what C on G said , and explains well.
I am going to switch to manifold vacuum. Ported vacuum seemed to be introduced to Increase engine temp at idle to drop emmisions .
If you have a distributor it's utter madness to disconnect the vacuum advance, and it's especially laughable that people think doing so is some sort of performance modification, switching from ported vacuum to a full manifold vacuum signal is however worthwhile experimenting with.
Following on from Eliot's earlier post I too run a fully mappable engine management system, this connects a manifold absolute pressure sensor to full manifold vacuum, data which is read by the ECU, to connect the MaP sensor to ported vacuum would be a very bad idea indeed.
As I start cruising at low load my ignition map actually runs a whopping 48 degrees, and under hard acceleration is goes to 34 degrees at peak torque, this delivers peak power under acceleration and maximum fuel economy when cruising. As I continue to accelerate and I pass through peak torque I'm actually pulling timing as engine speed increases, which is something you could never achieve with a distributor. Unlike a distributor my Canems can make changes to ignition timing completely independently of engine speed and load if required, this means you can build the perfect three dimensional ignition map without being held back by the compromises an engine speed governed distributor ignition system imposes.
For those still running a distributor the only way you can alter timing beyond what is governed by engine speed is to use a vacuum advance unit, the vac advance unit is therefore the closest thing anyone still running a distributor will get to a 3D ignition map. To disconnect the vacuum advance unit is therefore utter madness, it's like throwing away the only thing that actually makes the dumb distributor a slightly more intelligent and adaptive system.
I can't be any more clear than that, where you connect the vacuum advance unit (ported or full manifold vacuum) is up to you, but for heavens sake please don't disconnect it!
Forgetting standard cars of course.
If you alter the cam and port the head, would you need to modify the vac advance somehow to mantain the correct timing ?. Assuming you are running old school management.
I only ask as the curve would be altered as a result.
I assume this can be done using some modification. I have seen a few specialist talk about it.
I am not talking standard engine though.
If you alter the cam and port the head, would you need to modify the vac advance somehow to mantain the correct timing ?. Assuming you are running old school management.
I only ask as the curve would be altered as a result.
I assume this can be done using some modification. I have seen a few specialist talk about it.
I am not talking standard engine though.
Edited by ahpboxster on Saturday 14th July 13:56
Mine has been disconnected by the gentleman who did the rolling road tune on Wendy. My take off was at the plenum raather than at the butterfly and it was causing a couple of issues. He just disconnected it and compensated the mechanical advance.
In fairness, I had already discussed with him that I would be going Megasquirt so he took a 'let's get it to work' approach. Which I find very positive.
What ever he did, Wendy is a lively 350i
In fairness, I had already discussed with him that I would be going Megasquirt so he took a 'let's get it to work' approach. Which I find very positive.
What ever he did, Wendy is a lively 350i
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? If so, the Lucas DLM8 will have been designed and internally calibrated to produce ignition advance figures based on partial vacuum (or ported), by applying full manifold vacuum to a DLM8 the resultant ignition advance values will be too high?
Completely removing the entire vacuum advance feed pipe is puzzling! There has been much said in the past on whether to remove the damper valve and its orientation, perhaps some owners went the whole hog and removed the pipe as well.
Completely removing the entire vacuum advance feed pipe is puzzling! There has been much said in the past on whether to remove the damper valve and its orientation, perhaps some owners went the whole hog and removed the pipe as well.
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