ok,lets see if anyone can help..know a guy with a 430 detriot autoshift(former US express truck) averaging over 7.0 MPG.mine is a 470 detroit autoshift(former US express truck) that has trouble averaging over 6.0 MPG. both trucks are condo's-his is a 2000 production 2001 model with the 1.8 computer, mine is a 2001 production 2002 model with the 2.0 computer. i have yet to determine if we have the same gear ratios(i have his VIN).our miles on each truck is the same(760k).will reprogramming mine to a 430 yeild the same results(if possible)? does the 470 have larger valves/cam profile/etc?--the ONLY way i can get over 6.10MPG is by maximum 55 MPH on flat ground with light load. although the truck cruises real nice at 70,the mileage falls to 5.35 MPG while his maintains right around 7.0 MPG. seen other 430's with the same 7.0 programmed fuel mileage with 10 speeds,13 speeds,etc. my dash program is set at 6.0 so i'm actually getting what it's supposed to yet his is programmed at 7.0 with the same 12.7 liter engine displacement-nobody at any shops will tell me (even freightliner) what the actual difference between the 430 vs 470,and one even said that is was impossible to get 7.0MPG from a 430. i know for a fact he's getting 7.0 because i checked his OBD.what gives?????

Have either of you figured your mileage rather than going by the computer? I drove a freightliner with a detroit set at 450hp. and the computer was never right on the mpg.

i've checked mine by miles/fuel and it's REAL close. if not on the money.like i said i've seen many a 430 with the 7.0 mpg factory program(and yes i know you can change the "target MPG" on the display).some of the company trucks are getting this at Gardner trucking so i know it's possible. these are all 430's--the 500hp detroits are only getting 5.5-6.0.and the MBE freighliners are getting close to 7.0 with 450 hp(governed at 65mph)

The difference in horsepower could be why the mpgs arent the same. Also rearends would make a big difference. But one of the biggest could be the weight of your foot compared to your friends.

The rated hp does not really affect the tank mileage. It's horsepwer demand, how much of that horsepower is required to cruise.

If truck "A" needs 170 hp to cruise at a certain speed and truck "B" needs 140hp to cruise at the same speed. Truck "B" will obviously get better fuel mileage.

The exception would be if for some reason one engine design was less efficient at the mid horsepower level, but it's not that common in same brand engine.

If the operating techniques are the same, the differences are pronbabbly in truck/trailer configuration and load.
Just wondering, are both engines 12.7L?

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The HP difference is "fuel delivery". Max HP really has very little to do with mileage, until it's used.

With that said, "no two engines, trucks,electronics whatever are alike.
Load, road speed, wind,terrain and "idle time" are THE biggest factors in mileage.

As far as "gearing", just ask how many RPM he is turning at 55, 60, 65 whatever and compare the two. Most company trucks are 3.55:1 tho.
Which should put you around 1500RPM at 70. If you are turning less you probably have 3.36:1, but that would be a rarity.

A Detroit should be at about 1500 at hi-way speed for optimum MPG.
But less RPM on flat terrain and no wind will result in better MPG.

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we both have 3.55 rears,i checked his VIN.just did the overhead(tune-up) on mine,checked the program,turns out mine is set at 430HP already.i'll run it for 10k and see if there has been any change.