Thread: Ignition Timing
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fredmeister fredmeister is offline
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Join Date: Oct 2002
Location: Baltimore, MD, USA
Posts: 2,233
Garage
You should really check the entire function under vacuum and boost.
I found that idle timing of anything ATDC or even 0 degrees BTDC yields horrible off idle and low rpm performance. I could run faster than the car until 2500rpm.
It is important to limit advance to under 29 degrees at 4000rpm because detonation is the worst thing to happen to your engine. However, you don't want to get disappointed at low speeds if this forces a bad idle timing.
That being said, I time my 79 930 with the vacuum and boost hoses on my dizzy the following way.
Idle speed 950rpm timing to 4-6 degrees BTDC with vacuum hose connected. Remove the hose and see how far advanced it goes. This tells you how much vacuum retard the can is producing and check against specs from the workshop manual. If it don't work fix it.
Then I reconnect it and remove the boost hose and supply pressure to it with a small pressure hand pump and see how much it retards timing. This checks that the boost retard is working and how much you get.
Then run it up to 4000rpm and set the timing with the knowledge that under boost (when under load, not when checking it in the garage now) it will retard back that amount. This should be around 26-29 degrees max from what I see normally.
This gives me a good running car at low rpm around town and pulls hard when boosting.

I really wish some tuner experts would publish a timing chart that we could use for setting up our cars. Most of us here by now have modified the cars with k27 turbos and headers and a little more boost and I would like new data to go by that works.
I don;t want to destroy my engine until I find out the hard way. Plus who knows what distributor is on their 30 year old car, me being the 4th owner and being that Porsche supplied a few different versions over the years. California, US, ROW etc.
Which one has the ultimate advance curves and vacuum/boost retard features? lots of questions!
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"

Last edited by fredmeister; 02-11-2009 at 07:08 AM..
Old 02-11-2009, 07:01 AM
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