Is 25 mpg with a turbo 6.2 possible?

[Darren5531]

I have read the 6.2 and 6.5 max mileage threads multiple times. I have been reading as much as I can on mileage for some time now.

What can be done to a half ton truck geared to run at 1800 at 60 mph without lowering the truck or similar?

I don't have any truck yet or an engine to rebuild so I'm starting from scratch. I am getting a pathetic 24-25mpg in my little commuter sedan with a drop to near 19 in the winter. I am not a big fan of fords, don't have the money for dodges, and frankly I do like Chevys. So with not being able to afford a 4bt swap, the only really other option is a 6.2:).

Would a post-88 be better for fuel mileage or a pre-88? I would assume with the ifs, more gears, and overall newer technology would provide more efficiency but it seems the opposite from this boards statements.

Ideas so far:

Use "C" cup heads
Turn fuel up just enough to provide 6-8 psi of boost
High pop injectors?
Move air filter towards the front of the truck to provide cooler air
Free flowing exhaust (Dual 2.5" or 3")
Then all the normal things such as; tires and tire pressure, timing, fluids, etc.

Thanks for taking your time to read this book,

Darren

[Robyn]

I had a 1982 GMC Jimmy (Blazer) full size 4x4 with a stock 6.2 and 3.42 gears.
It would pull down 24+ easily on the highway and around 18 in town.
Once you turbo the little monster and up the fuel rate all bets are off as to what is gonna happen.
Power is easy to find, but with it comes the use of fuel to make it.

My 6.5 TD dually 4x4 3500 will do 18 hwy and that is not bad for a 7000lb truck with 4.1o gears.
If you gear and power for mileage its possible to see close to 25.

Robyn

[farmertracks]

I have an 85 half ton with 6.2. The pickup started life with an automatic, and it now has a newer NV4500 tranny with the mechanical clutch linkage in it. 25 is about the worst on mileage that I get with that pickup. It is a 4x4 also. I don't have it turbo'd, but I do have dual 2.5 inch straight piped exhaust on it that sounds awesome. I would guess you would lose mpg with a turbo on it.

[Darren5531]

If you don't mind could you elaborate on your set up some? Gearing, rpms, tires, any mods done to the truck besides the nv4500 etc.

I would assume that your rpms are quite a bit lower then 1800 which brings up the point do you really get the best mileage at Volumetric Efficiency or if cruising at 1500 or so?

[farmertracks]

The pickup is a single cab long box. It has 31x10.5 15's on it. 3.42 gears. It is a J series motor also. The intake and heads have been port matched, whether it really helped, I can't tell a difference. I do have air conditioning also on the pickup. I run around 1700 rpms at 65 mph, and rarely drive under that speed, except speeding up and slowing down. The pickup will run 100mph+. The exhaust has no mufflers what so ever, just straight pipes into 4 inch tips. It is not obnoxious in the cab at road speed either. The pickup has over 350,000 miles on it. Originally it was an EGR motor, with a 700r4. I found a military replacement motor that had 1200 original miles on it and put that in. Switched to a 4 speed manual when the auto trashed itself. I wasn't happy with the top end or fuel mileage at that point. My mileage is actually better if I would drive 55 or so, but I live 80 miles from anywhere, and I just can't make myself drive that slow. Most of my driving is around the farm with it, maybe 30-40 miles at a time. If I get on the hiway and run out a tank of fuel without stopping (better have a large bladder) it will do slightly better and you can drive forever it seems. I do have my injection pumped turned down a bit too, as I was after mileage, not power. I had to have it rebuilt last year, and when I got it back, I was getting 15-17mpg. The shop that rebuilt the pump put it back to factory specs. It would blow lots of smoke and ran pretty good. It will still blow smoke now, it may not have quite the power now, but I have other pickups for pulling.

[moondoggie]

Good Day!

The 82 in my signature had / has 31x10.5R15s, which may have actually hurt my mpg. It used to get such good mpg that I didn't even bother checking it, & that's saying something, because I'm probably the most anal person alive when it comes to mpg. It has two 20 gallon tanks, so I'd drive 400 miles & switch tanks. When I filled up, I had a chart on my visor that I made up that told me if I bought between X & Y gallons, my mpg was 25.0 - 25.9, or 26.0 - 26.9, etc. In the summer, this truck ALWAYS returned 26.0 - 27.9 mph. You must remember, however, I am also one of the 3 people in MN that drives at the speed limit. Also, my daily commute was just about perfect for maximizing mpg: 1 ½ blocks of residental streets, then ~ 5 miles of 55 mph four lane with (I think) 4 traffic lights, then ~ 20 miles of interstate at 55 mph, then ~ 5 miles of interstate at 65 mph. (mph corrected for odometer error, of course.)

I had the original red motor replaced on bad advice, to fix a head gasket leak that reoccurred. My mpg was never as good with the replacement 85 motor I had put in, but was still consistently 24.0 - 25.9 or so.

It sat at my buddy's place for a couple years, then I needed it quick when we had 2 wrecks in less than 2 weeks. It started immediately, & returned 24.0 - 24.9, which ain't bad, since I was driving it November thru February.

If you add a turbo AND keep your foot out of it, you'll probably increase your mpg 5% or so. Put the boot to 'er & all bets are off, except that your mpg will of course drop.

Blessings!

[moondoggie]

Good Day!

Oops, I forgot: the 82 has 3.08 gears.


Blessings!
(signature in previous post)

[arveetek]

I'd leave the turbo off if you're interested most in fuel economy.

According to GM, the 6.2L was capable of 31 mpg. I don't think that was very realistic, though.

Check out this vintage ad:

http://www.thedieselpageforums.com/photopost/data/500/medium/6_2_Diesel_Ad1.jpg

Casey