Mileage Question

[Roy W]

Periodically I read comments that refer to "keeping boost low" in an effort to achieve better fuel mileage. I'm confused.......I thought that increased boost resulted in better combustion, which should translate to better mileage. I understand that boost is directly related to engine load, but if you could maintain maybe 6 -8 lbs of boost at no load highway speeds, shouldn't your fuel mileage be better than say 3 -4 lbs of boost under the same conditions ??

[JohnC]

Periodically I read comments that refer to "keeping boost low" in an effort to achieve better fuel mileage. ...

Not sure where you saw that...

Boost accomplishes 2 things. First, it provides air (oxygen) for combustion and second, it lowers EGT's. Excess boost beyond that which is needed for these two purposes is not productive and results in increased back pressure due to the load presented by the turbine side of the turbo.

8psi at unloaded highway speeds would not buy you anything.

[Kennedy]

Boost can be an indicator of load with a fully mechanical turbo. In this case you have a computer controlled turbo so it is not so much a direct indicator. Boost is a key though and something tuners need to address. Unfortunately the generic stuff does not do this (good for me) which is why the LLY tuning tends to be hot and smoky with little to no MPG gains. When I do an ECM tune I add boost in some places and reduce in others. This is part of getting the best mix of MPG, performance, and cool/clean operation.

[Roy W]

Thanks for the comments guys. I'd love to have one of JK's custom tunes, but my Edge EZ and Boost Stick will have to do. (It has for the last 60,000 miles). It can't be doing too bad though as on a recent 1310 mile (GPS distance) trip I used exactly 60 gallons of fuel which translates to 21.8 mpg. Speed was 72-75 mph, EZ on #1, and boost at steady speed was 5 psi.

[NutNbutGMC]

Thanks for the comments guys. I'd love to have one of JK's custom tunes, but my Edge EZ and Boost Stick will have to do. (It has for the last 60,000 miles). It can't be doing too bad though as on a recent 1310 mile (GPS distance) trip I used exactly 60 gallons of fuel which translates to 21.8 mpg. Speed was 72-75 mph, EZ on #1, and boost at steady speed was 5 psi.The mileage statistics had nothing to do with the above info. It was the topper that got you the great mileage. :D

I couldn't do without a topper. :cool:


21.8 is impressive.