Distributer vacuum tube missing...?

[davep]

For those running ported it might be worth checking that the male take off has in fact been drilled through!

http://www.v8register.net/subpages/RV8NOTE258.htm

RAC has it wrong as well!

https://www.rac.co.uk/drive/car-reviews/mg-motor-u...

Edited by davep on Tuesday 17th July 09:09

[griff59]

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.
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]

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"

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.

[griff59]

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.

[davep]

ChimpOnGas said:

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...

"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 ....
.
.
.
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.

What also aroused my curiosity in the above MG RV8 info was this statement:

Note: The first time the car is started after this procedure a brief automatic readjustment of the ECU will be noticed but this will then settle down quickly. However if the ECU can not readjust to new vacuum advanced setup the timing will need to be reset, usually a few degrees before BTDC.

Now someone has obviously witnessed this and not dreamt it up, and seems to suggest that there are differences in the 14CUX EMS code for the UK and Japanese variants that may be associated with ignition timing; bearing in mind the signal from the distributor's ignition amp times the fuelling interrupts for the ECU. So I checked and there is indeed a specific 14CUX version for the Japanese variant that has numerous parameter differences to the UK's MG RV8 version (which is essentially the same as a TVR 4.0 tune). So this begs the question: does changing from ported to full manifold, and vice versa, alter the fundamental ignition timing curve that requires changes to the fuel controlling parameters in the 14CUX code? Has anyone looked at this?

Also, reading the MG RV8 blurb I get the impression full vacuum advance was also implemented on the Japanese version for 'sticky plaster' emissions control reasons.

Edited by davep on Tuesday 17th July 15:19

[ChimpOnGas]

griff59 said:

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.

As will the drivability improvements it gives

Please don't take advice from websites where the author says that full vacuum causes the timing to be fully advanced all the time, and please don't take advice from someone who uses the the non word Plenim and the nonsense term 'Butterfly Chamber', they quite clearly dont know what they're talking about!

For some inexplicable reason, somewhere along the way as the internet developed, it seems anyone who could create their own website was able to achieve instant credibility for any old bull they chose to present on it.

Don't get sucked in, a website is not a qualification!

Some of the most ignorant and ill informed shysters have the best looking websites, it doesn't make them an expert in anything other than putting their hand in the pockets of fools.

[griff59]

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.

Edited by griff59 on Tuesday 17th July 15:45

[ou sont les biscuits]

griff59 said:

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.

Edited by griff59 on Tuesday 17th July 15:45

The hose you need is this tiny diameter one. That doesn't get 'sucked flat'.

[ChimpOnGas]

griff59 said:

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.

Edited by griff59 on Tuesday 17th July 15:45

First of all and if you haven't got one already, you need to buy yourself a decent timing light (a strobe), preferably a 'dial back' timing light like this...



The above is an Innova 3568 which has been a loyal servant to me for many years since I bought it in the States, it also has a tach (rev counter) which is a very useful feature, other dial back timing lights are available. The important element is to understand how to use it and exactly why/what you're doing with it before you start, assuming you're confident to progress here's a useful post from Belle427 explaining his switch from ported to full manifold vacuum.

Belle427 said:

My findings are
12 degrees btdc static.
Full manifold vacuum, adding 6 degrees at idle so its roughly 18 degrees btdc.
Total timing all in 30 degrees.
Car is a lot more responsive low down, feels like its gained more torque.
Running temp also down by roughly 10 degrees on the gauge.
Cant see a down side to this modification.
As already mentioned you need to check your timing figures before carrying it out.
Every car will be different.

And here's a similar post from StuVT who also made the switch.

StuVT said:

Idle 8deg BTDC vac OFF which with
full vacuum the figure is 18deg BTDC. Vacuum taken from the plenum take off that was used by the fuel fume purge device.
This gives 26deg full mechanical advance at 3500rpm+ and around 36deg vac and mechanical for cruise.
Base idle set to 600rpm, which gave 950rpm with the bypass hose unclamped.
PcV fitted to the flame trap.
Fuel purge equipment removed.
All breather hoses jubilee clipped.

And here's his results....

StuVT said:

I finally got out today and it was a bit odd actually looking for traffic.

Anyway I am a convert. After letting it warm up I found a steep hill near Whipsnade Zoo and couldn't detect any pinging, all noises were regular and I have a slight blow on a V clamp for the Y piece but that is a regular sound and is always there, but at 26 full mech advance I doubt pinging will be an issue. I need to make some new det cans. Mine were rather perished and not ear worthy.....

I cruised the town centre where I know traffic builds.
The car is definately calmer to drive like this. There is a hint of shunting but its only slight and after a while I didnt notice it. It would cruise at 30mph in 4th at idle and in 1st and 2nd I got the revs to between 1200 and 1800 and changed the throttle position to stimulate slow traffic. This is where the possible diluted shunt, like a slight hesitation manifests itself.
I'm considering moving the distributor to the 22btdc mark I made at idle to see if this cures the slight hesitation. But to be honest where it is now is fine. I cruised the town centre traffic for an hour and it was relaxed and I actually enjoyed it. Before it was like river dance in the clutch and throttle to keep it smooth.

I know its arctic out there but the temp was just under 90c the whole time.

On the open road it pulls from idle up to the limiter smoothly and goes like a stabbed rat!

Off the national speed limit roads back into the town traffic and it stayed just below 90c and continued to crawl in traffic rather civilised again.

The only issue thats unchanged is the shift from 1st to 2nd is jerky. It may be me or a thing they all do, but I hoped this was connected with shunting.

Overall, very happy with it. So much calmer to drive in town.

ChimpOnGas - Thank you for sharing your findings.
Im seriously considering having the distributor modded to mimic your ignition curves at some point this year if you would be happy to share.

Stu

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

[griff59]

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.
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]

griff59 said:

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.
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?

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...

[griff59]

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.

[griff59]

AAARRGGHH! It's the wrong hose! I've managed to find one at Racetech, the original hose, should be here in a few days.

[Mr2Mike]

griff59 said:

AAARRGGHH! It's the wrong hose! I've managed to find one at Racetech, the original hose, should be here in a few days.

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

[Steve_D]

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

Ooooh look I wonder what this is going to be used for....



Steve

[griff59]

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.

[ChimpOnGas]

Steve_D said:

Ooooh look I wonder what this is going to be used for....



Steve

Nice one Steve, let us know how you get on with it

[davep]

griff59 for a possible answer to your original question 'Distributor vacuum tube missing..' have a read of this thread:

https://www.pistonheads.com/gassing/topic.asp?h=0&...

Look for the post by v8 racing, who is Rob Robertson of V8 Developments and has a good reputation in TVR circles, as this may explain why your car doesn't have vacuum advance and summed up with:

... this is definetly one of those questions that every engine builder will have a different answer too, all i can say is in my experience with ONLY THE ROVER ENGINE they do run a heck of a lot nicer in modified form with no vac advance

You'll also see much of the original source material for the manifold vacuum better than ported theory. Which in turn came from here:

https://www.chevytalk.org/fusionbb/showtopic.php?t...

... and is great info if you're running a 50s/60s carburated Chevy V8 engine. Also there's much talk of different vacuum cans and to LIMIT THE AMOUNT OF PULL PIN TRAVEL ON THE VACUUM ADVANCE, or, there will be way too much vacuum advance timing when it is plugged into full manifold vacuum.

Good to see people are getting positive results using full manifold vacuum on their TVRs though, the vacuum advance units on the 35DLM8 must be up to it.

Edited by davep on Thursday 19th July 13:17

[Rob_the_Sparky]

I suspect that what is going on is that in modified form the centrifugal advance in the distributer is no longer right (less right might be a better term) and taking off the vac advance is masking the real problem. Having said that I know GoG has done a lot of tuning so would be much better placed than me to comment.

Rob

N.B. Thanks to CoG for the research, I understand the function of the vac advance and had been wondering why people block them off.

[ou sont les biscuits]

davep said:

griff59 for a possible answer to your original question 'Distributor vacuum tube missing..' have a read of this thread:

https://www.pistonheads.com/gassing/topic.asp?h=0&...

Look for the post by v8 racing, who is Rob Robertson of V8 Developments and has a good reputation in TVR circles, as this may explain why your car doesn't have vacuum advance and summed up with:

... this is definetly one of those questions that every engine builder will have a different answer too, all i can say is in my experience with ONLY THE ROVER ENGINE they do run a heck of a lot nicer in modified form with no vac advance

You'll also see much of the original source material for the manifold vacuum better than ported theory. Which in turn came from here:

https://www.chevytalk.org/fusionbb/showtopic.php?t...

... and is great info if you're running a 50s/60s carburated Chevy V8 engine. Also there's much talk of different vacuum cans and to LIMIT THE AMOUNT OF PULL PIN TRAVEL ON THE VACUUM ADVANCE, or, there will be way too much vacuum advance timing when it is plugged into full manifold vacuum.

Good to see people are getting positive results using full manifold vacuum on their TVRs though, the vacuum advance units on the 35DLM8 must be up to it.

Edited by davep on Thursday 19th July 13:17

The key word in the quote from V8 developments is modified. If you read the thread referred to modified means really lumpy cams and extensive work on the heads and other bits and pieces to make the engine flow as much air as possible.

How close a standard TVR 5 litre engine is to one of those is something I'll leave others to comment on. But there is going to be a cross over point on the tuning spectrum up to which vacuum advance is going to help, and after which it won't.