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 Twin input vacuum regulator
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thesaabologist
V4 Fanatic

319 Posts

Posted - 14 Aug 2010 :  09:55:41 Show Profile Reply with Quote
My Sonett had all the US emissions gubbins (until I removed them last week). The vacuum regulator has two vacuum connections - one from the carb and one from the intermediate plate.

I am looking to change the intermediate plate to a standard V4 one (which will enable me to fit a Weber 34ICH) but this will elimate that vacuum connection. Can I simply ignore the input on the vacuum regulator or do I need to swap it for an earlier single input regulator? If I do that do I need to change the distributor also?

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1974 Sonett III

Borstlap
V4 Fanatic

Norway
279 Posts

Posted - 14 Aug 2010 :  17:12:58 Show Profile Reply with Quote
Swap only the vacuum regulator for one with a single vacuum connection. I don't know if it should be earlier or later (is there a difference in vacuum advance between various models), but maybe it is best to opt for one that was used on standard European spec cars of the same year.

Alex
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Woody
V4 Guru

United Kingdom
2443 Posts

Posted - 15 Aug 2010 :  12:27:56 Show Profile Reply with Quote
Here are scans from my W/S manual relating to the US distributor. It would appear the vacuum unit is retained by two screws and the actuating arm to the breaker plate should have a small E circlip.
Could you not plug the pipe that goes to the US intermediate plate and continue to use the external one to the carburettor? The 1972+ distributor 0 231 170 031 has a vacuum body which might suit but the screw holes may not align on your US body. The simpler solution would be to employ a 72 UK distributor.






Edited by - Woody on 15 Aug 2010 12:34:31
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thesaabologist
V4 Fanatic

319 Posts

Posted - 15 Aug 2010 :  22:59:55 Show Profile Reply with Quote
quote:
Originally posted by Woody


Could you not plug the pipe that goes to the US intermediate plate and continue to use the external one to the carburettor? The 1972+ distributor 0 231 170 031 has a vacuum body which might suit but the screw holes may not align on your US body. The simpler solution would be to employ a 72 UK distributor.


Was running it until now with the intermediate plate plugged and the input in the vac device venting to air - when it was all connected up the car ran badly at temperature and disconnected it was much better - I can't quite figure out the physics of what benefit would be obtained by plugging that input.

I agree that the cleanest solution would be to switch to a UK distributor - however would the curve be right for a 1.7?

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1974 Sonett III
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Woody
V4 Guru

United Kingdom
2443 Posts

Posted - 15 Aug 2010 :  23:53:59 Show Profile Reply with Quote
I am not aware that 1.7s had different curves. Will have to have a closer look at the manual which is in the Troll at the moment. I used to run a 1730 motor back in the 80s with a 1971 uk distributor with vac advce. It had gas flowed heads, rally camshaft and rally valve springs, 28/36 on SAH adaptor and a rally exhaust. It ran very well apart from having worn balance shaft bearings.
It would be interesting to try a 72 UK distributor in yours to see if it ran better.


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rsimps
V4 Guru

United Kingdom
1616 Posts

Posted - 16 Aug 2010 :  07:44:51 Show Profile Reply with Quote
It should be fine with a uk dizzy. There are about three different advance curves for the different ages of car. The later one (most common) is probably your best bet for a std engine.
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thesaabologist
V4 Fanatic

319 Posts

Posted - 29 Aug 2010 :  23:30:54 Show Profile Reply with Quote
Done some more research into this:

The back side retard function is not really necessary and the car will run better without it - I noticed this when I disconnected mine.

Port on the back of the vacuum unit is controlled by the pressure present under the throttle and retards the ignition when the throttle is closed. Apparently this retard feature was a temporary stop-gap measure by Saab to help control/reduce emissions but it did so along with a reduction in fuel economy.

I contacted Ashcraft, they advise that a standard dual-unit will only pull about 5-6 degrees and an old unit rarely will pull more than 3-4 degrees. They advise that a new vac unit will pull 8-9 degrees, so will give better/smoother running when running higher octane fuel.

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1974 Sonett III
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Jan van Vurpa
Starting Member

USA
32 Posts

Posted - 30 Aug 2010 :  20:57:08 Show Profile Visit Jan van Vurpa's Homepage Reply with Quote
Boys all the 13 dizzies I know of for all the various V4s all have the advance "full in" by around 2200 rpm, so makes little difference ultimately.
the 'received dogma" in the US is that the "68" advance curve will transform the motor into a fire breathing monster sling falming blobs of napalm like burning rubber all over the road, other cars and passers-by, leading to total pandemonium...
Never noticed it myself.

As for fitting an ICH, the only intermediate plate that works worth a damn is what I call the "'69" intermediate plate ie the one with just 2 fittings and no square decel valve like USA post 71 cars had---a horrible blocy thing ported to interplate, which has a horrible diaphragm at the bottom which, like the accel pump diaphragm, always ruptures and cause a nasty air leak (which mechanics invariably call "vacuum leaks" (leading to visions of the whole world being sucked into the vacuum below the throttle plate.)
The non power brake 67-68 intermediate plate with just one fitting for the PCV valve will work even better,,, some tweaking of the cable mount for the choke will be needed.

Edited by - Jan van Vurpa on 01 Sep 2010 20:58:14
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rsimps
V4 Guru

United Kingdom
1616 Posts

Posted - 01 Sep 2010 :  08:05:07 Show Profile Reply with Quote
On a std engine any of the advance curves are fine. On a comp engine I use the early dizzy, max advance comes in about 3200 rpm (engine rpm not dizzy rpm, which is half). All the other dizzy come in later, so require the initial spring softening up. For a rally-race cam you want max advance at about 3200rpm to 3500rpm and a limited max advance at approx 38 deg, with vac advance locked out. Anything less than a rally engine, you probably can get away with a normal dizzy and vac advance.
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rsimps
V4 Guru

United Kingdom
1616 Posts

Posted - 02 Sep 2010 :  12:20:02 Show Profile Reply with Quote
Basically you need to double the rpm on the diagrams. The later uk dizzy gets max advance at 4500 rpm which is ok for a std to mild modd'd engine, but too late for a competition unit. You will be loosing some power in the mid range.
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