3-5% Gas in the Oil, NA BBC MPFI
 

Has anyone experienced 3-5% gas in the engine oil with a naturally aspirated BBC with multipoint fuel injection and mild dynamic compression ratio of 5.83 (~9:1 static)?

If yes what was the cause if the cause was determined?

My base engine is a Mer 496HO but heavilly modified to ~600hp but still naturally aspitrated. The ECU is still the Merc PCM555 but fuel table recalibrated to provide AFR's from low 12's to low 13's in support of the higher hp. The fuel injectors are the stock 496HO's.

sure, when they re mapped they screwed it up and it is wildly rich at some point in the curve no matter what you think your afr
is. if it was just a bad injector i would expect it to run on 7... on the other hand if you are running the motor too cold or w/out a thermostat ( or the water temp sensor is bad ) it will be rich as hell as well.

Rage,
My 565" NA motor runs close to 13afr at WOT. Some high 12's, but close to 13.. The low 12's can do it. Calculating fuel useage I am in the 700-750hp range.
Hope that helps.
Dick

Thanks for the info stevesxm.

I personally data log all my own AFR (idle to WOT) and (other than the initial engine breakin before I sent the AFR data off for the latest ECU recal and that was followed by an oil change) the AFR has been 12 and above for the full rpm range under light moderate and heavy load simulations using trim trab induced hull drag. There is one big exception just noticed. When cold the idle ARF is ~12.0 but after warmed it drops into low to mid 11's. That is probably my biggest problem. I knew I wanted to recal one more time to further improve a couple of rpm ranges but now the idle is the top priority and then see what kind of gas % shows up in the oil.

My AFR target is low 13's for idle and cruise and high 12's for the rest.

I retained the closed cooling of the 496HO but changed the thermostat a long time ago with first engine upgrade from the 160F to 120F following the GM HP3 race engine specification so the engine cooling runs 138 - 140F unless pushed hard.

Yes it helps. Thanks.

What % fuel do you get in your engines oil and how do you run your engine?

I can tell you on mine that anything in the 11 range my plugs are trying to gas foul at idle.
One thing I am curious about is when running a aftermarket cam (I assume you are) does injector timing come into play?

I am running the Gen II HP3 race engine cam. The fuel table recals have been done by Dustin Whipple on the stock Merc 496HO PCM555. Injector timing modifications has never been mentioned, only pulse width, but that is not to say it is not an issue. I just do not know. I will ask.