avg. crank case pressure vs. BMEP?

A question (probably a dumb one ) for the engine experts. Does the "average" crankcase pressure track with the average BMEP? i.e as BMEP increases does crank case pressure increase? Assume an engine is set up to run on the "back side" of the power curve at a lightly loaded rpm higher than peak power and using crank case pressure to assist fuel flow. Then, as the engine loads up: rpm decreases, BMEP increases (with decreasing RPM, I think...) would the average crank case pressure increase delivering more fuel pressure (and more fuel) thus enrichening the mixture as the engine moves back up the power curve towards peak power?

>A question (probably a dumb one ) for the engine experts.
>Does the "average" crankcase pressure track with the average
>BMEP? i.e as BMEP increases does crank case pressure
>increase? Assume an engine is set up to run on the "back
>side" of the power curve at a lightly loaded rpm higher than
>peak power and using crank case pressure to assist fuel
>flow. Then, as the engine loads up: rpm decreases, BMEP
>increases (with decreasing RPM, I think...) would the
>average crank case pressure increase delivering more fuel
>pressure (and more fuel) thus enrichening the mixture as the
>engine moves back up the power curve towards peak power?

Ron B.
F4Fguy

The short answer is..........maybe.Since as you noted,MEP usually peaks somewhere south of peak HP,and peak MEP is where pumping losses are lowest relative to pressure,you would expect to see some relationship.On the other hand,the pumping losses,to a large extent, are what cause the differences in peaks so it's probably a wash.The rate of volume change in the tank due to fuel consumption is minimal between the conditions(or else you've got a lot bigger problems to worry about).What it comes to is;the case pressure is primarily dependent on the crankcase compression ratio and the pumping efficiency at any given condition.This in turn is controlled more by flow losses and tuning(especially if piped)than by load changes.If there is an effect,it's very likely not noticeable except on a very sensitive dynomometer.