Fuel Mileage, RPM ?

[bullboybob]

Hello everyone, I have a few questions. Truck specs are 2000 GMC Sierra Crewcab 6.5TD 3500 Longbed Dually
rolling on Michelin LTX LT235/85R16/E

the truck is semi stock right now except no cat and no muffler.

what is a good tire pressure to run no load ?
what is ideal Engine RPM for best mileage ?
what should I expect in fuel mileage ?



I have on the way a 3 in. Downpipe 4 in. system and a cold air intake
should the expected economy change much.

thanks for any help

Azrael

[Kennedy]

Your tire selection is a good one both size and tread/compound. From there, my best advice is slow down. While there is some correlation with RPM to MPG, I believe wind load has the most impact. You undoubtedly have 4.10 gears and the extra wind and rolling resistance of the duals does not help so I'd guess around 15-16mpg. You can re-gear and gain a bit, but you will lose the pulling power especially at moderate speeds.

[6.5 Detroit Diesel]

Best mileage is typically to be found 1,700-1,850 RPM's, from what most members have reported. 1850 will put you around 57-58 mph with 4.10's. However, with my 4.10's, I found out that highway driving, I got better mileage pushing the engine at slightly over 2,000.