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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Richard,

It is great to see you here (finally a real ignition expert) helping us learn more about ignitions. I learned two new things from you so far.

The length of spark duration on an inductive system and the timing drift info.

I still need to learn which is a better fit for a CIS single plug that probably has poor Air Fuel mixing and less than ideal / lean AFR's at low compression operation off idle. A spark that lasts 10 times longer or multiple sparks that last for x degrees of crank rotation.

The concept I have heard is you never know if you are going to have a proper mix with CIS at the spark gap that ignites properly with a to lean mix. This seems to come from the metering plates slow responsiveness (mass) and being isolated from what is going on at the intake valve but about 5 feet of plumbing, a turbo, an intercooler and the intake manifolds volume on a system that has not acceleration enrichment that is speced to run at about 14/1 AFR untill boost enrichment is achived at about 5psi. This is on top of the poor mixing that comes with an injector that has to spray fuel 100% of the time at low to high pressure maxing it possable that we might see somthing like 17/1 or 12/1 (a guess) at the spark plug gap.

What do you think is best or is there any improvement to be made?


The idea that timing might float as much as 5 deg scares me and might be another reason the stock 930's might be conservative in there timing values.

What are we to do to get better off idle response with the lean surge and poor air fuel mixing that comes with a very low compression 930 short of twin plugging?

Lastly, if you could help us with what we should be thinking a max safe timing advance number might be for a typical CIS build 930 runing street fuel, it would be highly appreciated!

Stock seems to be about -16/-19 to up to -23 on a C2 Turbo at .8 bar. We have one member here ruining -25 on street fuel at .75 bar boost. I am very confused as to what a reasonable expectation might be.

So please, what might a single plug and twin plug look for as a starting on boost advance timing limit for say .8 an 1 bar boost. CIS tends to run a bit fat at
TQ peak as you know and gets leaner at hight rpm.

Thank you in advance for your time and info if you can help.

The best.

Last edited by 911st; 04-27-2010 at 08:55 AM..
Old 04-27-2010, 08:52 AM
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