6.0L Mileage with Highway Gears

[fleming442]

Has anyone done an LS 6.0 as a highway cruiser? I originally wanted to do a 5.3, but might be able to get a whole 2500HD cheap. I already have an '02 Silverado 2500HD that gets 12mpg on 31's with a 4.10 rear. I was just wondering what half the weight and gear would be like in ye olde Bonneville.

 

[cyrus_the_great]

holden comodore/caprice got a 6L and highway gear plus alittle heavier than a gbody got 13.5L/100km combined

 

[olds307 and 403]

If you use a gear like 3.42 and taller tires, your rpm's will stay nice and low, should help a lot. Depends if your keeping the EFI and 4L80E. I have heard as bad as 9 mpg out of the 6L trucks, they just don't get near the mileage as the 5.3. That said, the 5.3 is a suck fest in the trucks I drove, only the 6 spd auto makes it tolerable.

 

[bigmandengo]

I had a 85 cutlass in 2011 with a cammed lq9 and t56 and 3.73 rear. With that car, I've had highway trips with 27 mpg. Even trips to the dragstrip with multiple runs down the track yielded low 20s mpg. Now, I have a 5.3, 4l80e, 3.25 rear car and the gas mileage seems much lower, however I haven't calculated it yet. I would attribute the better mileage to the t56 with its long overdrive and a lower power loss through the drivetrain.

 

[fleming442]

Bigmandengo, that is quite impressive! Since the donor truck will be a 4x4, I will probably ditch the short (no) tail 4L80E. I will probably end up with a 4L60/65E. I was actually thinking an electronic 5 speed would be cool, but they were only available for a year or two, I think. I know the 60/65 series will make most question reliability, but, like I originally posed, it's just a highway cruiser. I might take it to a TnT if I ever get it done just to see what time it puts up. I'm not looking for a brawler, though a pea crap green, LS 4 door might catch a few sleeping.