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I remember when cp-e did some testing with their 135. IIRC they found 12.5 was the optimal for 12 psi. Above that did not result in any power. Below 12 power was 5-10 hp lower. I tried searching for the thread but can't find anything from them anymore on this board.

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Originally Posted by TrackRat

"Safe" depends on your definition. DI engines may run safe at a slightly leaner AFR than a typical EFI engine at WOT, but they don't make as much power when run lean enough in most cases to satisfy current emissions and mpg goals. Stoich is for best fuel economy not power. You'd never want to run at stoich for max performance and reliability at WOT.

The DI engines are designed to get better mpg and lower emissions. Running closer to the ideal AFR for max power delivers better power and reliability but poorer mpg and emissions. It's common to run less ignition timing with lean mixtures or high boost because you simply have no choice or you experience detonation. Timing of less than 17 degrees in a 4V engine at WOT from 5,000 on up typically leads to very high exhaust gas temps because the engine wants more ignition to fully burn the charge in the cylinder before the exhaust valve opens for blow down. Lots of compromises exist to deal with mpg and emissions in current engines.

The bottom line is 11.3-11.8 AFR at WOT provides good power and reliabilty in a properly designed 4V engine with proper cylinder and head heat rejection properties, modest ignition timing, 92 octane fuel, etc. A leaner AFR in a forced induction engine will make more power up to around 12.5:1 with retarded ignition timing, but at the expense of engine reliability. In addition most dynos have very poor AFR accuracy so take all the dyno data with a large grain of salt if they aren't also using a $100K Horiba exhaust gas analyzer.

YMMV

That is good info. So you like my second AFR better that I posted?