Pre ignition

Boosted M5 · 09-28-2019, 02:31 PM

Quote:

Originally Posted by SmokinJoe

Quote:

Originally Posted by F10CPROG

Knock as we all know is usually caused by too much timing advance and or being too lean fuel mixture.

I'd get it on an AFR meter to check it. Maybe change the O2 sensors as these are very sensitive on the S63tu.

Not sure can be done on a stock engine with regard to timing, maybe get a tuner to check it and adjust as required. Get a reputable stage 1 map put on with a touch of extra fuelling and a degree of retard to keep things safe?

I had an afr probe in it while on the dyno. Showed very similar afr to the data logs I did. Again these were pretty lean at 14.7-1 until almost 5k rpm then tapers to low 13s high 12s by redline. Fuel trims are only a couple % give or take so it’s getting what it thinks is correct. Wonder if it could just be 1 bad injector causing 1 cylinder to be super lean. Probably wouldn’t show up any different at the o2 sensor if it was just 1 cylinder. Also only made 503whp. It was a hot day being 95 degrees out. Still think it should have been a little higher.

At 14.7-1 all the way to 5k I'd say that's a pretty good tune. 14.7-1 is "ideal" combustion for gasoline. The mass of air is exact for a complete combustion of the fuel; after combustion there is no excess oxygen in the exhaust and no unburnt fuel. As rpms get higher so does timing advance hence you want afr to dip below 14.7 at that point to save the motor. Now if you want the car to run rich all the time that's a whole different story. Are you running pump gas that's top tier?

SmokinJoe · 09-29-2019, 01:37 AM

Quote:

Originally Posted by Boosted M5

At 14.7-1 all the way to 5k I'd say that's a pretty good tune. 14.7-1 is "ideal" combustion for gasoline. The mass of air is exact for a complete combustion of the fuel; after combustion there is no excess oxygen in the exhaust and no unburnt fuel. As rpms get higher so does timing advance hence you want afr to dip below 14.7 at that point to save the motor. Now if you want the car to run rich all the time that's a whole different story. Are you running pump gas that's top tier?

14.7 is stoich for gasoline but most engines run a bit more rich under heavy load especially when boosted. Direct injection is a bit different and can usually be safe at leaner afr’s then a port injection motor. A little extra fuel helps prevent knock by keeping things a little cooler in the combustion chamber. I know they run lean as possible for fuel economy and emissions regulations. I don’t want it to run rich I just don’t want it to ping itself to death

For fuel I use Chevron and 76 both 91 octane. I have also tried adding boostane octane booster bringing octane to 95 with little change.