I should have given thomas some more background the first time...

Anyhow, I'm confused by this: "i was wondering if i got straight open exhaust on it if it should get better mileage... i've heard that diesels don't require any back pressure from the exhaust to run right but i had exhaust on it a while back and it seemed to get 10 mpg anywhere!?!" If you "had exhaust" on it before and got 10, but are getting 14-16 now- presumably with exhaust ("the truck doesnt have a turbo or a cat all it has are the mufflers") what's different?

I am suspicious of Red's (or his friend's) claim of a four inch system yielding a 20-40% mpg increase. It flies in the face of everything I *think I* know about exhausts. Plus, if it was true, you can bet it would have come from the factory that way.

On a different note, it seems to me if you are getting better mpg in the city than on the highway, you are likely burning up too much fuel by pushing massive amounts of air aside with that big square sled. Also, high speed is the enemy of that old-skool tranny w/o lockup converter and OD. Slowing down, being steady or using cc, and airing up those nice high psi, highway tread tires should help.

There are many vehicle mods and driver techniques that remain consistant whether you are driving a ZX2 or an Excursion. Instead of repeating them all again I would urge you to do a search here for all the wonderful knowledge that's already posted.

The guy does drive like an @$$ and the thing is lifted, sitting on 38" boggers so it might be off some....

Yeah... Given that a driver can double or half the EPA rating, I would guess that it's kinda hard to attribute any mileage change at all to the exhaust.

The American carbs that Harley tried to use for years were unreliable. Those same Japanese carbs are on our ATV's, Jet Ski's, & even lawn mowers. The only thing better is FI.

Dave

6.2 is an N/A diesel so bigger exhaust probably won't help too much. if you could get your hands on a turbo kit for that it would greatly improve the milage and power.

this article may help even though it is performance oriented the concepts work for milage too.

https://www.dieselpowermag.com/tech/c...dup/index.html

I don't think adding a turbo will increase FE at all. Changing to a smaller engine with a turbo probably would.

without adding fuel it will add a little power but make the engine more efficent

I don't see how. A turbo uses exhaust pressure (which comes from pistons) to cram in more air; the fuel injectors add more fuel to match, don't they? Or does it just run leaner because diesels run widely varying ratios? If it just runs leaner, then you're using the pistons to push exhaust to turn a turbine to push more air into the cylinders...sounds like a recipe for loss unless it was running too rich beforehand.

the 6.2 runs pig rich when pulling any load. A turbo would lean that out and make use of the fuel rather than wasting it as black smoke. the main reason a turbo would help milage is the 6.2 n/a has 145hp but with a turbo it makes 60 hp more. This will move the 6000+LB Suburban much better than the N/A could ever do. The banks power pack claims 10% increase in milage with an increase of 60hp and 115 lb/ft.

I just ordered a 3" downpipe for my powerstroke to go with the 4" exhause it had on it when I bought it. Will post the results when I get it installed