Does PSI (boost pressure) make a difference in gas mileage? If you have 2 100% identical vehicles, 1 is set at 18psi and the other is set at 12psi, would the one with 12 get better mileage because it has less horsepower?

 

Well, I wouldn't call it a hoursepower thing, the 12 psi car is using less fuel then the 18 psi car due to the amount of air being used for proper combustion.

 

well depends



are you driving both cars exactly the same way?



besides who cares about gas mileage on a boosted vehicle anyways

 

I assume this is in reference to stock turbo

I assume this is driving sedately to optimise gas mileage



It shouldn't make a difference then. All that adjustment means is that the wastegate will crack later on, but in regular driving, you are almost never making full boost so it's not an issue.



It would use more than 1/3rd more fuel though. A stock turbo designed to run at 12 psi will be getting very hot and wheezy at 18 psi.