1988 C3500 Gas Mileage
 

My 19 year old got his first car. It is a 1988 Std Cab C3500. It has a TBI 454 in it with a TH400 and 3.73 gears in the back. The tires are 30 inches tall. The gas mileage is awful. My question is, is it that because of the 3.73 gears in it? The engine must be running OK, because it passed smog. (California).

My 91 2500 454 Suburban got OK gas mileage, but it had an Overdrive auto trans in it and the rear end gears were not that low.

If it is a rear end gear issue, what would be a good street gear ratio for this? He does not tow anything.

Re: 1988 C3500 Gas Mileage
 

Welcome to the board! All I know to say is this: He's 19, with a big block, and a non-overdrive tranny. I'd be shocked if his mpg broke into double digits, regardless of rearend ratio.

Re: 1988 C3500 Gas Mileage
 

My '88 crew cab dually is square body, but that shouldn't make a huge amount of difference. It was born with a 454/TH400 and 4.10s. Even after swapping the TH400 for a 5-speed, the truck still doesn't see more than 8mpg.

A higher gear might help some, but the real issue lies under the hood. You just can't expect much mileage from a 454.

23. ;)

Re: 1988 C3500 Gas Mileage
 

Lol, I was talking about the driver:lol: I remember how I drove when I was 19...it's basically the way I drive now, at 31...

Re: 1988 C3500 Gas Mileage
 

Oh. Gotcha. :lol:

And at 34, I don't drive much differently than when I was 19 either. My insanity is just more polished and skilled these days. :metal:

Re: 1988 C3500 Gas Mileage
 

Its a 1ton truck its gonna be hard on gas.

Re: 1988 C3500 Gas Mileage
 

8mpg....every 454 Chevy gets 8mpg. The key word is 8mpg...:waah:

Re: 1988 C3500 Gas Mileage
 

Well then heck. I am going to build him a 10.5 to 1 396/402. I have enough parts laying around to do that. What I will need is Adjustable Electonic Controls for the TBI to compensate for the the smaller CIs. The problem with the 454 is that the stroke is too big for the Connecting Rod length, and the compression is too low. We will see.