4x4ord wrote:
The DI gasoline engines are no longer regulated to a 14.7 air/fuel ratio nor is the compression ratio limited. Preignition can't happen without fuel being injected.
I haven't heard about DI engines no longer being regulated to 14.7:1? What engines are these?
Every DI I have hooked my OBD Torque App up to from my Ecoboost truck to my wife's old Audi(both turbocharged) have been regulated to an A/F of around 14.7:1 with a very narrow range. The only time either engines ran lean was the brief instant after going WOT it would add too much air before the injectors could compensate. It would go no more than 15.0:1 though. After that it would run rich at 13.2:1 if you left your foot into it and then start to go back to stoich as you picked up speed. In normal driving or idle they always stayed around 14.7:1 +/- .5. My diesel on the other hand will go anywhere from 20:1 to 80:1 depending on engine load. At Idle, it will go even higher than that to upwards of 100:1.
I know some DI engines have high compression ratios like the 6.2L Ecotec with 11.5:1(probably why 93 octane is recommended), but I have not heard about any mass produced DI engine getting to the 15:1 and up compression ratios of diesels or the 17.3:1 of my Cummins.