33's and 4.56's

[6.0vortecchevy]

well right now i have 373 and 33, i get 11 around town and about 12.5 on the highway. Averaging 75 mph. I have a set of 456 waiting to be put in and i was just wondering if you guys think that will help or kill my mpg. Im thinking that it will turn more rpm's on the highway but the vacuum will be lower since it wont take as much gas to maintain that speed. let me know what you guys think.

[1BadCC]

its gonna kill it. A 33 isnt much bigger than a stock z71 tire. I think my 01 z71 tire measured out to like a 30 or 31.

[Frenchy]

You'll get better mileage around town for sure.

[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.

[BuiltZ71]

I'm pretty sure 4.56's and 35 inch tires,are equivalent to a stock tire and 3.73's..so it should have a better take off,but turn higher rpm's on the highway..so it'll probably be worst on the highway..I have 35 inch tires,on a 20 inch wheel..running 4.88's it sits around 2500 rpm's,at 75 mph..hope this helps

[6.0vortecchevy]

what you get for milage?

[BuiltZ71]

I'm not real sure,I can't keep my foot out of it long enough to get a decent estimate..I'd say prob around 12-16 on the highway..

[ls1ram]

Sorry if i missed it, but what are your goals with the truck? 1/4 performance? current mods? How much do you drive on the highway? what % vs in town?

If you are able to adj shift points and lock-up control then you may be able to get lockup in 4th sooner at a lower mph. This might help with mpgs. On my Camaro my tuner said nothing less then 48 mph for lockup with my 3600 stall in my camaro...I didn't feel like this was good, converter just kept slipping at crusing speeds 38-48 til lockup. I had him change it to 38mph even though he didn't agree...and the car is alot more streetable and gets better mpgs by 3mpgs in that 38-48mph range...my car is 3.73 with a 26in tire so your 33's and 4.56's is about the same with me just having less weight...

[6.0vortecchevy]

Yea i have efi live so i can change all that. Its just my dd that i like to take to the strip in once in a while. Its has already has a circle d converter and cam. Just wanting a little more off the line. Its getting a true trac when i put gears in since it already has traction problems.

Oh and I do about 32 miles a day going to work and back on the highway.