Tapping single vac advance distributor for boost retard?

turkish · Post by **turkish** » Wed Jun 24, 2009 9:41 am

I see that it is possible to tap the stock fuel pump to make it boost sensitive, just wondering if it is possible to do the same on a single vac advance distributor? I'm trying to do as close to a 100% stock turbo setup and I'm having trouble finding a dual vac distributor. So far I've got the boost regulatoed stock pump, a VW branded turbo off a Passat and going to blow through the stock carb. Basically the only non-factory parts will be the exhaust, various oil lines, an MSD 6AL box and possibly 1.4 ratio rockers but I might just adapt some 1.25 TIV's.

fgronlun · Post by **fgronlun** » Wed Jun 24, 2009 12:11 pm

I think that it is not possible to modify the std Vac advancer. But the rest of the distributor is okay to use with turbo.

Interesting engine spec you have. Couple of months ago i built almost with same spec a low low budjet 1500/1600 engine. Only not standard part where the exhaust and the turbo.
In that engine I used the standard type4 injection distributor and i think it worked ok..

Here i have some pics of it.

Only problem with this setup was the STD carburator. It was imposible to get any higher boost than 0.8.

Of course i had to test it on a dyno and here i have the chart of it.
Firt run is with 0.4bar boost then 0.6 and the last one is with 0.8bar.
Hp values are in wheel horsepower so if you want to calculate it to engine horse power it is only to ad 14-16%

67stang302 · Post by **67stang302** » Wed Jun 24, 2009 3:28 pm

turkish wrote:I see that it is possible to tap the stock fuel pump to make it boost sensitive, just wondering if it is possible to do the same on a single vac advance distributor? I'm trying to do as close to a 100% stock turbo setup and I'm having trouble finding a dual vac distributor. So far I've got the boost regulatoed stock pump, a VW branded turbo off a Passat and going to blow through the stock carb. Basically the only non-factory parts will be the exhaust, various oil lines, an MSD 6AL box and possibly 1.4 ratio rockers but I might just adapt some 1.25 TIV's.

I actually just finished building a boost sensitive single vac advance dist. it required two parts dist. to make on and I am currently working a on adding some adjustability to it. once I am done moving this weekend I will post pics of it all assembled and all the parts I used

fastback · Post by **fastback** » Wed Jun 24, 2009 4:09 pm

when using the dual working vacum canister
it retards the ignition a whole 12 degres only on very low boost 5 psi.
i welded a chunk of alu to it , drill and tap to fit a screw that can limit the retard from 0-12 degrees.

Post by **Piledriver** » Wed Jun 24, 2009 4:44 pm

Adapt a dual vac can to a single vac distributor, I personally wouldn't bother trying to hack a single vac can, it's just not designed to go both ways, missing required spring internally in addition to the obvious fitting.

Nice work, Fastback.
BTW, I'll be looking closely again at your engine install for ideas.

mike thompson · Post by **mike thompson** » Wed Jun 24, 2009 5:34 pm

Having the dual can is not critical. When you say single canister, does that mean it lacks a centrif. advance? I suppose not.
What is critical is to limit the cent. advance because the stock advance is set up to make up for very little initial advance (smog settings).
I run ten initial and 14 cent. (total as measured at the crank). + when idling or crusing the vac can adds a bunch. Oh and run your vac line to the full vac fitting on the carb. The "Port" vac.was for emissions purposes and actually worsens your idling fuel usage. This is easily tested by noticing how much rpm your engine goes UP when connected to full vac.

Post by **Piledriver** » Wed Jun 24, 2009 9:06 pm

Ummm... Mike, ported vacuum advance is required for decent efficiency, not just emissions.

You absolutely do not want to connect straight to manifold vac, and as ported vac advance is plumbed the way it is, it has NO effect on WOT performance.

The dual vac can simply allows boost retard used as we are discussing, the retard is vented to atm, disconnected..
(Assumes a blow through setup)

I'm with you on recurving for more initial/less range, but different setups need different amounts.

I may have misunderstood what you were trying to say, sorry if that is the case.

mike thompson · Post by **mike thompson** » Thu Jun 25, 2009 6:58 am

Well, I have been running straight vacuum (below the carb type) since before there was such a thing as ported vac. As I said, ported came about as a consesion to emissions. Prior to the 1970s ported did not exist.
And no, if you want efficiency use straight vac.

Post by **Piledriver** » Thu Jun 25, 2009 7:48 am

If you want ~35 degrees of advance at idle, go for it.
I suppose on a stock advance setup, it could work.

I'll just enjoy the improved design, efficiency wise it should make little>no difference running down the road.

turkish · Post by **turkish** » Fri Jul 10, 2009 4:47 pm

I greatly appreciate all the advice, but I found a dual vac with electronic points replacement on the other site for $55 so I will be going with that. Now, what do I need to know about setting the dual vac up for boost retard? I'm really liking fastback's setup, I was thinking of trying to make the attatchment between the vac can arm and where it hooks to the distro adjustable but your method seems alot easier. I know there are going to be limits as far as getting timing exactly where I want it but how close am I going to get to having full 32deg advance when not under boost and 24 under 8-10lbs.?

fastback · Post by **fastback** » Fri Jul 10, 2009 4:57 pm

well as long as u have a way to limit the travel of the canister on retard u can adjust it.
set your air compressor on approx the boost level u want to run
start the engine and apply the airpressure to the canister
then adjust to 8 degrees retard.

my_medusa · Post by **my_medusa** » Sat Jul 11, 2009 12:45 am

interesting post.
I use a dual working vacum canister from a saab9000 turbo on my supercharged 36HP engine and it work great with 14 psi of boost and up to 5000 RPM. wunderful idla at 650RPM like a clockwork, and exelent power all over the RPM and load.
I will also make the total late setting changable during the next 2 weeks because I have some exams right now.
I think vavuum on daily drivers is very usefull, i can drive my engine all the time without boost (suck trough principle) and my boost moves like the pedel on every RPM.
btw- i use the stock dizzy ov my '56 engine.

i will make a pic of the changed tin and inner side nect week.

fastback · Post by **fastback** » Sat Jul 11, 2009 1:36 am

nice
do u have any idea of how many degrees the SAAB canister retards??

my_medusa · Post by **my_medusa** » Sat Jul 11, 2009 2:34 am

no...i will messure the mm what the lever goes under some boost levels because its in the original dizzy from my 36 hp engine.
and then i will make the total stroke adjustable.
original there is a touch on the tin that fix the total stroke.

maybe there are some informations in the net or saab could say how the tin exactly works.
here is a small video of the characteristic of a 36hp engine

that was with totally stock exhaust, now I fist change only the end pipes 20,5mm to 28mm inner diameter and the sound + power + charakteristic increased (exaust was such a brake).
http://www.youtube.com/watch?v=jqP9L2heyq0

fastback · Post by **fastback** » Sat Jul 11, 2009 5:21 am

smooth car!

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Tapping single vac advance distributor for boost retard?

Tapping single vac advance distributor for boost retard?

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