[911st]

Cole,

Thx! I am sure I still have alot to learn and am glad to get your imput.

Everyone wants to run 12/1 AFR w big boost and they are not looking at the ignition side.

I am concerned that many of us are running to much advance on boost and do not even know it.

I suspect that the original stock setting at -26 US at 4000rpm may not be enough for a built car. Again, Bruce Anderson notes setting it to -25 for a car that runs .9 bar or has limmited runs to 1 bar. That was written years ago and I think before we started getting the gas with alchol in it. Also, one ignition sheet I was given showed that timming on boost was pulled back with more boost retared of about 1.7 through 1 deg more when going from .8 to 1 bar boost. Thus, we might want to look at setting timming at about -24 for a car with a health unmodifed igntion if running more boost.

We need to build safety in to the tuning of a 930. It dose not have the ability to adjust timming and fueling with temp or altitude like the more modern cars.

Timming on boost is directy tied to full timming is set at on these cars and is retarded about 8-10 deg from that setting. Anyone that sets there timming at -29 probably better be running race fuel because they could be at -20 on boost and need to be as low as -15 or so.

Yes, run the best fuel possable but set up your car to work with what ever you usally run.

Detonation is not directly tied to timming. Pre-ignition is. Detonation is when there is ignition from heat or compression before the spark.

Anyway. When I was big on understanding CIS I concluded that one of the reasions for the high rate of failures with 930's was because of the potental for uneven fuel flow per cylinder (others say uneven air flows).

As such I am a big beliver is having the injectors cleaned and matched and the head ballanced so we are not in a suituation where we think we have a healthy AFR of say 11.3/1 on boost but have one cylinder at 14/1 with the others at 11/1.

Now that I am looking at the 930 ignition side it looks to be succeptable to failure. If the vac hoses are not in good shape or the diphram in the retard-can is leaking we will not get retard and will be pulling -25 deg when we should be at about -15. This system dose not fail toward retard. If fails and we get no retard but do not know that is what happened.

Also, there is a little solonid on the vac-ret side of the can the seems to be essential to getting boost retard. That solonoid really needs to close on boost. If it dose not, both sides of the can recive a boost signile that should cancel each other out. I suspect if that happens, we will not get our boost retard.

One member I talked with thinks the dist has some magic in it that if the dist dose get an equal boost signle to both sides of the retard-can it will still retard against its spring. It would be good to have someone put a hand pump tee'd to both sides and add pressure to see if this is true. I am very suspect.

If I were doing a 930 I would 'look at' removing the Vacuum-Retard side at the can so I would not have to wate for the vac to go away to get my advance and to protect me a little bit more from failure.

Thus, we are probably running to much timming to begn with for a motor that is running higher boost, we probably have less than ballanced AFR's at each cylinder, and have a higher than average suseptibility to ignition failure that would limit our boost-retard without us knowing it.