does BACK-PRESSURE increase MPG vs straight thru...

[marcus]

got it thanks..it does make sense...its just there is a theory that back pressure allows the engine to reuse unburn fumes that stays on the enginedue to backpressure.to get a better gas mileage..???

Originally Posted by at3GG

meaning if your exhaust gives you 5hp but you drive it exactly the same as before, theoretically your mpg should increase because you have more power pulling the same weight. However, most of us like to use the extra power that we get so it will basically cancel out any mpg gain. Think thats what he meant basically?

[yaris-me]

Originally Posted by marcus

got it thanks..it does make sense...its just there is a theory that back pressure allows the engine to reuse unburn fumes that stays on the enginedue to backpressure.to get a better gas mileage..???

You missed the point about velocity and scavenging by MadMax. To reuse exhaust gas would be a valve timing design. That helps to keep the temperature lower to allow for a leaner burn.

Reducing back pressure can get you a slight increase in gas mileage, but there is a point of diminishing return. That is what we don't know. For that you would need to consult an engineering expert.

[GeneW]

Originally Posted by yaris-me

You missed the point about velocity and scavenging by MadMax. To reuse exhaust gas would be a valve timing design. That helps to keep the temperature lower to allow for a leaner burn.

That's what the EGR (Exhaust Gas Recirculation) is for. Changes the chemistry of the gas mixture. If memory serves correctly it was originally meant to allow leaner mixtures to be used without pinging.

Gene