33's and 4.56's

[ls1ram]

I think it depends more on the tune..if its set good on the lean cruise then it should get better mileage all the way til about 65-70 mph or at least within .5 mpgs...in town should be slightly better if not stay the same..I would think over 75 mph you will still be fighting air and mileage will drop.

I have 3.90's on a 31 in tire and when I first did the ls1 swap in my truck I swapped a set of 27's on there...I drove on the interstate and it seemed to get better mileage at 65mph...It seemed to take less throttle position to keep the truck moving...Sorry but I do not have mpg results, I just remember it doing good on the 120mile trip to the track..

As far as vacuum goes, you have it backwards. less throttle will create more vacuum as you are now closing the blade and sucking all the air away from the intake plenum, but this is good. Now with more throttle position and less vacuum the engine is under a load and starts to loose velocity...this ends up in a less efficient atomization of fuel in the chamber...more unburnt fuel..less mileage....

If you like to run your truck hard and race time to time then I vote for 4.56's!!!!!! keep it around 65-70 on the highway instead of 75mph, get a good tune and tell who ever tunes it what you are looking for. and enjoy!!!

There seems to be alot of posts about people thinking of 4.56's and worried about mpgs....But I have yet to see one where someone has 4.56's and complains about mpgs or performance...That should tell you to pull the trigger!!!

[6.0vortecchevy]

Yea I just worded bad the vacuum thing, but i understand it. I guess il just install the rears and drive it around for a week or soo to see. and if don't change then I think ill do the fronts.