reactor2

I was wondering how a large overlap cam (111, 112) affects the AFR ratio in a boosted application, particularly under load at WOT? That is, since the intake and exhaust are open longer at the same time there is a point when the blower is just blowing air (even air and fuel) right out the exhaust potentially "faking" the WB out into believing that the motor is running leaner or richer than it really is.

Is it potentially "off" 2-3% over a more reasonable overlap blower cam (i.e. 116lsa)? That is, for example, on a boosted application with a large overlap cam when the WB tells me its 11.8 would that be equivalent to a 11.4 on 116lsa cam (reading leaner than it really is), or would it the other way around, 11.8 on a large overlap cam would be 12.2 on a 116lsa cam (reading richer that it really is)?

For certain, a large overlap cam will have an effect on the AFR but the question is, which way (leaner or richer) and to what extent?


Thanks!!

stevieturbo

It's a good question...but I imagine very difficult to actually get a proper answer.

Overlap is bound to give a false lean reading to some degree.

reactor2

I could see it giving a false rich reading as well, depending on the overlap and when the injector fires. Possibly another reason why boosted applications shoot for a afr in the 11s?

stevieturbo

It will give you a false lean reading, meaning in reality you are actually much richer.

For most part, when injector fires wont matter. It's the air passing through the engine during overlap that will skew the sensor. Nothing else.

Lambda sensors only measure excess oxygen.