mcoleman

That's a very untrue statement. Most trucks get better mileage with mods as long as you keep your foot out of the new found power.

rharveysr

Hey Dusty...
It could have something to do with your right foot!

Rick

need12v

I'll second this notion. In OTR trucks, pulling the same weight, a 525 CAT will get more MPG than a 425, because the engine is not working as hard.

That being said, I have seen cranked up mechanical 425's get WAAAYYYY better mileage and have more power than an electronic 525.


I'm interested in the cam timing thing now. It makes sense that it would be a factor, and you know, guys that build hot V-8s for dragsters and the like are all the time degreeing cams...

Haulin_in_Dixie

If you are pulling heavy all the time, the 24 seems to do better bombed or stock on mileage and out pulls the 12 in most cases. Better breathing, flexable timing. It says something that going up a grade you have to downshift and pull hard with one and just stay in top gear all the time with the fuel drinking higher horsepower. I could count on 12 to 13 at 30,000 pounds with my 24, never saw a 12 that would duplicat that at the same power levels.

JAX

After the FASS and the new Injector Pump I am constantly getting better than 20 even around town. On the highway I can count on 23-25 as long as I keep it at 65.