Distributer vacuum tube missing...?
Discussion
For the first time yesterday I showed my car to other club members, while looking at the engine it was pointed out to me that the small pipe that should go from the vacuum diaphragm on the distributer to the air intake manifold is actually missing. There are blanking plugs inserted at either end too. What's more mystifying is that a new diaphragm ring has been fitted to the distributer, so why bother to do this if you're not going to fit the pipe?
Is there any reason at all why the pipe may not have been fitted?
Is there any reason at all why the pipe may not have been fitted?
bobfather said:
It's not good to have unmetered air going into the plenum. If you decide to leave the vacuum pipe off you should blank off the plenum tapping to prevent air being drawn in
I had a word with my dealer, he said that they normally leave the pipe disconnected, then adjust the timing, which on my car is spot on. The plenum tapping has been blanked off, so has the diaphragm end at the distributer.RichB said:
Just out of interest, my Griff 500 has never had a vacuum advance, so the chaps at the Blackpool factory did not fit them, or at least not in March '99 they didn't.
Interesting, have you tried connecting it?I'll have a go a see if it makes any difference.
PS, I've trawled the net for photos of Griffith engines, it's very interesting that far more have the hose disconnnected than connected.
Edited by griff59 on Wednesday 11th July 17:30
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!
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.
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"
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.
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
ChimpOnGas said:
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
Both of those points are why I posted my question, the only reason I can think of for people disconnecting these hoses is because it's more suited to flat out running, on high performance cars, not my theory, only going by what a lot of other people have said. The RV8 in standard production cars was probably destined for day to day driving duties, and not tampered with.Why would Rover fit the hose to manifold vacuum then block it off, that makes no sense whatsoever
My Griff has manifold vacuum, I asked once before but no one came back to me, do I have to readjust the timing if I put the hose back?
Mr2Mike said:
Further proof, if any where needed, that the service side of the automotive industry has more than it's fair share of people who lack fundamental knowledge and critical thinking skills.
The reduction in heat dissipation from the exhaust manifold at idle is probably even more valuable than the economy improvements for a TVR.
Well, the reduction in heat probably makes it worthwhile. The reduction in heat dissipation from the exhaust manifold at idle is probably even more valuable than the economy improvements for a TVR.
The hose thickens...
I've managed to locate some vacuum hose, the guy said ordinary hose wouldn't do, as it would "suck flat"
OK, do I just fit it and forget it, or do I have to get the engine re-timed?
PS, hose bought, this should be interesting.
I've managed to locate some vacuum hose, the guy said ordinary hose wouldn't do, as it would "suck flat"
OK, do I just fit it and forget it, or do I have to get the engine re-timed?
PS, hose bought, this should be interesting.
Edited by griff59 on Tuesday 17th July 15:45
ChimpOnGas said:
As we can see both the above Chimaera owners have been extremely happy with the results of their the switch to full manifold vacuum , others have since followed suit and are all reporting the same positive outcome. This is no surprise really as the idea is all based on scientific fact I have taken great care to support with clear factual evidence presented on these pages and the original post over in the Chimp cage, please take the time to read all 8 pages as along with the detail in this post.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
To help further here's the ten step process to switching from ported to manifold vacuum:
1. Warm the engine thoroughly, a couple of fan cycles is good
2. Remove the vacuum advance hose from the plenum end at the throttle butterfly (ported vacuum) and block the nipple
3. Use your dial back timing light to check your ignition timing at idle and record the figure, you should be seeing 10-12 degrees at 950rpm
4. If the figure is greater or lesser than 10-12 degrees you'll need to loosen the distributor clamp bolt and correct your timing by turning the distributor
5. Now connect the vacuum advance hose to full vacuum
6. You will immediately find your 950rpm is now elevated by as much as 150rpm or more
7. Return your idle speed to 950/1,000rpm by winding in your base idle screw
8. Recheck the timing using your dial back timing light, you should find you're now idling at 18 degrees, IE 12 degrees mechanical + 6 degrees from the vacuum advance unit you've now connected to full manifold vacuum = 18 degrees of idle timing
9. As a final check rev the engine to 3,250rpm or more and use your dial back timing light to check your total advance, this will only be mechanical advance even with the vac advance still connected as there's little or no vacuum when you open the throttle enough to reach 3,250rpm. Your total timing will therefore be no different to what it was when you ran ported vacuum, IE 12 degrees at idle + 18 degrees of mechanical advance = 30 degrees which is completely safe BTW
10. Go for a drive and enjoy your new smoother TVR
Remember when you're accelerating and the engine is under load which is the only time you risk detonation you're opening the throttle so you're going to lose vacuum, so dont think because you're now idling at a vacuum advance assisted 18 degrees you're going to end up with all out timing number of 18 + 18 = 36
. It simply doesn't work like that because when you're accelerating the loss off vacuum means the vacuum advance unit adds nothing, you'll actually get your un-vac assisted 12 degrees at idle + 18 degrees of mechanical advance = 30 degrees of total timing which as I say is completely detonation safe 
However, the 18 degrees of vacuum advance assisted idle timing will give you far cooler exhaust manifold temps and a better quality more stable idle, but be aware like this the car will also very likely fail the MoT as emissions will be significantly increased. There are many advantages to switching from ported to full manifold vacuum, the biggest one being the constant vacuum at idle, just off idle and in the shunting zone applied to the vac advance unit gives far more consistent and stable ignition timing.
Basically the more consistent and stable source of vacuum at idle & very small throttle openings removes the timing spikes ported vacuum inflicts on the engine as the throttle butterfly passes back and forth over that port at the throttle body, as others have already proved.... you will definitely feel the difference
I really appreciate all this, but it's beyond me. I'm going to have to get my local TVR guy to do this for me, I can fit the hose, but that's it. But there's no point in me doing that without re-timing the engine, so I may as well get the whole thing done by someone else. https://www.pistonheads.com/gassing/topic.asp?h=0&...
To help further here's the ten step process to switching from ported to manifold vacuum:
1. Warm the engine thoroughly, a couple of fan cycles is good
2. Remove the vacuum advance hose from the plenum end at the throttle butterfly (ported vacuum) and block the nipple
3. Use your dial back timing light to check your ignition timing at idle and record the figure, you should be seeing 10-12 degrees at 950rpm
4. If the figure is greater or lesser than 10-12 degrees you'll need to loosen the distributor clamp bolt and correct your timing by turning the distributor
5. Now connect the vacuum advance hose to full vacuum
6. You will immediately find your 950rpm is now elevated by as much as 150rpm or more
7. Return your idle speed to 950/1,000rpm by winding in your base idle screw
8. Recheck the timing using your dial back timing light, you should find you're now idling at 18 degrees, IE 12 degrees mechanical + 6 degrees from the vacuum advance unit you've now connected to full manifold vacuum = 18 degrees of idle timing
9. As a final check rev the engine to 3,250rpm or more and use your dial back timing light to check your total advance, this will only be mechanical advance even with the vac advance still connected as there's little or no vacuum when you open the throttle enough to reach 3,250rpm. Your total timing will therefore be no different to what it was when you ran ported vacuum, IE 12 degrees at idle + 18 degrees of mechanical advance = 30 degrees which is completely safe BTW
10. Go for a drive and enjoy your new smoother TVR
Remember when you're accelerating and the engine is under load which is the only time you risk detonation you're opening the throttle so you're going to lose vacuum, so dont think because you're now idling at a vacuum advance assisted 18 degrees you're going to end up with all out timing number of 18 + 18 = 36
. It simply doesn't work like that because when you're accelerating the loss off vacuum means the vacuum advance unit adds nothing, you'll actually get your un-vac assisted 12 degrees at idle + 18 degrees of mechanical advance = 30 degrees of total timing which as I say is completely detonation safe However, the 18 degrees of vacuum advance assisted idle timing will give you far cooler exhaust manifold temps and a better quality more stable idle, but be aware like this the car will also very likely fail the MoT as emissions will be significantly increased. There are many advantages to switching from ported to full manifold vacuum, the biggest one being the constant vacuum at idle, just off idle and in the shunting zone applied to the vac advance unit gives far more consistent and stable ignition timing.
Basically the more consistent and stable source of vacuum at idle & very small throttle openings removes the timing spikes ported vacuum inflicts on the engine as the throttle butterfly passes back and forth over that port at the throttle body, as others have already proved.... you will definitely feel the difference
I've bought a length of silicon hose, the right diameter, but it's not the item shown in the picture with the fittings at either end, I take it it's not essential to use that part, and normal hose will do?
ou sont les biscuits said:
Here's a quick search for ebay items with vacuum advance pipe. Just buy something that looks about long enough. I'd tell you how long it needs to be, but my car doesn't have a distributor any more.
https://www.ebay.co.uk/sch/items/?_nkw=vacuum+adva...
I've bought a meter of the right diameter silicon hose, I'll use jubilee clips to secure it, what more can I do? I'm sure I don't need that proprietary hose kit with the terminals at each end, surely a push fit hose will do. https://www.ebay.co.uk/sch/items/?_nkw=vacuum+adva...
Mr2Mike said:
Why not buy the proper vacuum advance hose with the rubber end fittings, as per eBay link above? You can get 1m of the hard plastic hose with end fittings for £3.40
I've ordered one from Racetech, should be here in a couple of days, it's about eight quid, I'm EvilBay phobic.Rob_the_Sparky said:
Not really, but there is a point where the advance curve defined by the bob weights and springs in the distributor (the centrifugal advance curve) will no longer be appropriate. If you have an electronic system the first thing you do is to tune the set-up but with a distributor this is more tricky and in most cases not changed. I'll leave to those with more knowledge how much tuning gets you to a point where this is critical. I suspect it is just easier to not try to fiddle with the internals of the distributor and simply to disconnect the vacuum advance to allow more static advance to be used. As said though will wait for those more experienced to comment at what point this is significant.
I had a word with my TVR guy yesterday, I'm taking the car to him when it's time for its next service, he's going to check the ECU to see if anythings been changed, and either leave alone, or reconnect the hose if necessary. That's really the bottom line on this whole thing, as it's becoming even more boring than watching paint dry.The car runs smoothly, no shunting, and feels fine to me, that's not bad for an 82,000 car.
I'm enjoying it and that's the main thing, I wasn't even aware of this hose until someone pointed it out and ruined my day...
Edited by griff59 on Friday 20th July 09:20
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