Thread: Odd AFR issue
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mark houghton mark houghton is offline
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Join Date: Jul 2008
Location: Central Washington State
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Originally Posted by WERK I View Post
The best way to monitor A/F is through data logging under a rolling dyno, but for those who do not have one of those readily available, data logging with something like a Innovate sniffer works very well.

The ideal AFR for a 930 has been beaten to death and for good measure, crucified. It seems it gets richer and richer and richer with each passing thread. My 0.02, because the 930 pancake intake manifold provides less than ideal air distribution across all 6 cylinders and AFR's are the average of all 6 cylinders sampled, you may want to run a little to the left of the peak "Horsepower" curve around 11.8 to 12.5 AFR's. Some even go richer than that, thinking if a little rich is good, more is better. Keep in mind these AFR's are meant to protect from lean conditions from induction compromises and preignition which are variables depending on ignition timing, single versus twin plug, fuel quality, induction - stock versus modified, valve timing, etc.

The closer to stock the engine is, the closer to 11.8 the AFR should be. The closer to ideal the induction system is, the closer to 12.5 the AFR should be, for MAXIMUM POWER, that is.
I'm with you....good summary of this much maligned topic. My AFR settles in to about 12.2 on full boost (sometimes a little lower, depending on ambient air temp). That's 12.2 at .8 bar. At 1.0 bar, I'm usually at around 11.6. So much depends on the state of tune, as you've said. Like many, I'm tempted to adjust for lower AFR's....just to add a little more safety factor....but then where do you stop? I guess we would never feel completely safe until AFR's are so low that raw gas is drooling out the tailpipe and your turbo has turned into a ramjet.
Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 04-07-2010, 02:23 PM
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