Gas milage ?

[Pinger]

245/75R16

More road or off-road orientated is what I was suggesting. Can make quite a difference to mpg I'm told.

 

[Jerryred94silvy]

More road or off-road orientated is what I was suggesting. Can make quite a difference to mpg I'm told.

I went from my best tank getting 12.5 with BFGoodrich KO tires to getting 14 with street tires. So tires are definitely a factor.

 

[TravisR]

The 4.10 gears aren't going to be great for fuel economy. What's the speed limit on your drive? The 4L80E is more parasitic than a lighter duty transmission, as well.

 

[L31MaxExpress]

The 4.10 gears aren't going to be great for fuel economy. What's the speed limit on your drive? The 4L80E is more parasitic than a lighter duty transmission, as well.

I still got 18 mpg highway on a 2,200 mile trip with a 4L85E and 9.5 14 bolt with 3.73s in my Express van running 75-85 mph. Marine intake, marine cam, 1.6 rockers, thorley headers and factory dual 3" exhaust piping with high flow cats and a walker dynomax bus muffler.

 

[TravisR]

I still got 18 mpg highway on a 2,200 mile trip with a 4L85E and 9.5 14 bolt with 3.73s in my Express van running 75-85 mph. Marine intake, marine cam, 1.6 rockers, thorley headers and factory dual 3" exhaust piping with high flow cats and a walker dynomax bus muffler.

Well, 3.73s are quite a bit different. And a 4L85E? Is that in a 2002+ van or did you swap it in? If it's a 4.8 or 5.3 LS engine in a 2002+ van, then it's going to be more fuel efficient than a 95 5.7L. If you got 18 mpg out of a 6.0L... then congratulations lol that's great.

 

[Turbokat]

Well, 3.73s are quite a bit different.

I went from 3.42 10 bolt to a 4.10 9.5 14b and honestly i barely see any difference in MPG with my 5.7

 

[PlayingWithTBI]

I went from 3.42 to 4.11s also with my 5.7TBI and didn't see much difference either. Cruising @80MPH I'm turning ~2700RPM - right in its power band.

 

[L31MaxExpress]

Well, 3.73s are quite a bit different. And a 4L85E? Is that in a 2002+ van or did you swap it in? If it's a 4.8 or 5.3 LS engine in a 2002+ van, then it's going to be more fuel efficient than a 95 5.7L. If you got 18 mpg out of a 6.0L... then congratulations lol that's great.

Its a 97 with a newer 4L85E in it. Was a 5.7 Vortec engine. I have 5.13s and a 383 that makes around 525 hp now. Still see 17+ running 3,000 rpm at 70 mph. Gearing just makes the engine work less to get you rolling and allows it to run uphill with very little load. Vans still had a 5.7 in 2002 BTW. It was not until 03+ that they went LS. The heavier P30 vans and the cab over trucks had 350s until atleast 03.

 

[L31MaxExpress]

If I stay out of my secondary throttle bores I get very good fuel mileage even around town with the 383. Its a 1200 cfm 4bbl throttle body. I have my PE set to kick in right where the linkage picks up the 2nd set of throttle bores and starts to open them.

 

[SuperTramp]

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I noticed an improvement in mpg after I cleaned TB and intake and replaced the EGR valve.