924Board.org

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

Did anyone disconnect their vacuum can and is presently just running mechanical advance?
If so, do you have a part throttle issue?
Street car only.
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1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

welder · Joined: 16 May 2003 Posts: 158 Location: cumberland,maine

My understanding was that you couldn't do that without actually changing over to a "centrifugal advance" distributor,cause you needed the correct weights inside for proper timing. I don't think that a stock vacuum distributor will work without the vacuum. On a VW you can buy a kit to make this change. I can see how that without proper internals and no vacuum there would be throttle issues. I wonder if Bosch makes a kit for the 924? I would think getting rid of vacuum advance and going to a mechanical advance that would get you much better throttle responce. I think Applebit, or 924RACR are the guys to help here.
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I have a 78 n\a currently under restoration.

crazyinkc · Joined: 10 Nov 2002 Posts: 226 Location: Olathe KS

I thought this has been covered before. The 924 distributor has centrifugal advance under the breaker plate. You could recurve the distributor for the curve you want. I did run my car for a little while with out the vac. advance when I had my carbs and it ran good but I always wondered how much better it would run with it.

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

I'm in the process of getting the springs for a re curve.
It will bring in full advance around 3500 rpms compared to the 4500 its at now.
I like the vacuum unit for part throttle in 4th and I think it also adds 10 degrees to the total timing.
You get just 30 degrees with the can disconnected
I ran without it for a short trial and the car had more low-end torque.
It’s a prelude to what the new springs will feel like.
If I go any less than 3500 with the vacuum can on I might get to much advance at low rpm.
That’s why I asked about removing it.
I would like to maybe take full advance down to 3000.
But I think the stock setup will work best at 3500.

I can't wait to find out!
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

endwrench · Joined: 07 Dec 2002 Posts: 1631 Location: Victor, Montana

Where are you getting the springs from? I run mine with the advance side hooked to ported vacume and leave the retard side disconnected. this seems to work well. Have you had your distributor apart yet? Mine is a 1979 unit and they are a bit tricky getting apart and back together!

Todd

Joes924Racer · Posted: Mon Mar 15, 2004 12:32 pm Post subject:

my cans gone and I run like endwrench.
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1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

endwrench · Joined: 07 Dec 2002 Posts: 1631 Location: Victor, Montana

If things work out well I would be happy to split some of the cost with you in exchange for the springs. What kind of curve are you looking for. I personally would like to see 22-24° total distributor advance all in by 2800-3200 engine RPM. A set of stop bushings could probably be crafted to keep it from over advancing if I remember right. Been awhile since I had mine apart.

Todd

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

endwrench · Joined: 07 Dec 2002 Posts: 1631 Location: Victor, Montana

Capping it at 24° would flatten the curve as compared to 30° but I was actually considering the "total" advance with initial added in. I figure an initial advance of 8-12° would give a total advance of 32-36°. This is geneally accepted as the window of optimum advance for best performance. The more efficiant the combustion chamber design, the less total advance is needed. I suspect the 924NA will run best at the upper end of the scale (36°). Other things such as compression and fuel quality will also limit the amount of advance that can be used. Mechanical advance is great for perfomance but not so good for fuel milage. I think hooking the advance side of the vacume advance to a manifold vacume source would probably cure some of this though if it doesn't screw with the idle quality too bad.

I would definetly appreciate a set of those springs when you get them figured out! You must know somebody with an old distributor machine? I hate to think how many of those went to the junkyard over the years! I'd love to get my hands on one now!

Todd

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

I set up a curve using my pump pulley in marked increments. Very easy to do.
With the stock distributor vacuum hoses plugged, my stock dizzy reaches full advance at 30.
I run 5-6 BTC so we should be at the optimal 36 with the quicker curve.
The question I always had was that the full advance test from the manual says 41 degrees at 4500 rpm.
That would put us at about 11 BTC to reach that goal.
It would be a lot more work to increase our stock distributors mechanical advance and I'm not willing to run at 11 degrees static.
I had trouble turning the starter when I did and it ran very hot.
I like the vacuum can for part throttle driving, hills so
I think were on the same page.
I'm looking forward to the outcome.
I have some maintenance to do before I can sink the money into the springs.
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

endwrench · Joined: 07 Dec 2002 Posts: 1631 Location: Victor, Montana

Have to admit I have never actually checked full mechanical advance on my distributor. The thought of letting my engine freewheel at 5000 rpm long enough to check makes me cringe a little! At what rpm did you get your 30°? I run mine at 10° initial and have not had any problems so far but I have not had a chance to drive the car too much since putting it together. Less than a thousand miles. I am running 9.5 to 1 compression though and no ping or heat problems yet. I have a feeling the manual is wrong (again!) as I would have to be running 51° of total advance above 4500 rpm and I am sure this is not the case. I would have some serious detination problems evident by now. Let me know if you need some help defraying the cost of the springs when you are ready. I'm not actually ready to tackle this project right now anyway as I am tring to get my EFI setup going first. No hurry on this end!

Todd

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

II hit full advance at 4500 and it held steady to 5000.
Yes--I did cringe and wait for projectiles to start flying at my face.

It was not fun.
I think I forgot to calculate in the vacuum advance /retard into the total advance equation.
I'm thinking the vacuum retard is the only way keep a regular idle and hit 41 degrees full advance.
I tried to check it today to see what it added/subtracted.
I had timing light in hand when people showed up to work.
Thanks for the offer on the springs.
You got me thinking- I'm going to check my curve again.
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.