gas milage of a cucv

[tim292stro]

When you get it rebuilt, remember to have it built to the torque not the HP. A lot of local tranny shops here in CA will build it based on a HP number and assume you have a gasser - tell them it's a diesel, but also tell them the torque you're running. A 200HP engine at 6400RPM will output 164lb-ft of torque, but the factory J-code 6.2l diesels will do ~131HP at 2100rpm, meaning you are outputting 330ft-lbs of torque, a 100% increase in torque over the higher HP gas engine. If possible, have them build to at least 425ft-lbs...

 

[rsh4364]

340/19 = 17.89, yup that's about 1.1MPG better than the previously reported 16.8MPG - engineering math is engineering math.


Air cleaner with the wide open exhaust isn't going to do much (maybe another 0.5MPG or less) until you put in a turbo - then you want the restriction to be as close to atmosphere (nothing) as possible. Turbo especially if you see any altitude over 2000' above sea level - like making voyages south east into West Virginia... Note that if you do the turbo, you will not be doing headers - the turbo manifold pulls both sides into one turbo collector, and then out one pipe. Again, low restriction after the turbo will be your friend.

3.73 is more common than 3.9 - the original ratio for the M1009 is 3.08 - VERY tall. This was in part due to the lack of overdrive on the three speed transmission. If you can do the 3.73 ratio change when you pop in the 700R4 transmission, you should hit the butter zone for this power plant on 33's. It's an amazing revelation when you've hit the efficiency zone for an engine in a tuned drivetrain....


I think these trucks prefer "finer vintage" rather than being labeled "outdated". Most like elder more experienced women. If you can manage to control yourself a bit with the right foot (no jack-rabbit starts, and keep it below 60MPH always - I know it's hard with those truckers out in Ohio), you could probably squeeze out 18-19MPG now.

I knew I shouldn't have used the term outdated,not my term but the general opinion.(my GF),when I re gear it will be all new gears.I have 2 1009s my first is a 100k plus rusty model with the 308 gears,it usually got 20 mpg.My newer 86 1009 has a new motor,trans and rebuilt T/C,so Im trying to build it right for the long haul.And when it comes to the Stans headers I just want to hear one of these 6.2s with a set.

 

[Sergeant1983]

Driving my M1009 as a daily driver under best conditions.
17 mpg city 45 mph or lower
22 mph hwy 55 mph or lower
with M116 trailer loaded down 12 mph combined

 

[rsh4364]

With 4.56 gears and a 700r4 trans in od final gear is 3.42,With 410s and 700r4 final gear is 3.08,with3.73 gears with 700r4 final gear is 2.79

 

[tim292stro]

If you scroll back to the post where I link the ratio calculator, you can see roughly what the engine revs vs. the road speed is. Terminology I am using is that the "final drive" is the gearing in the differential(s), meaning it's the last or final gear-set power goes through before the wheels.

For 65MPH, unlocked TC, engine rpms would be (roughly):
With 700r4, 4.56 final, and 33" tires = 2232RPM
With 700r4, 4.10 final, and 33's = 2007
With 700r4, 3.73 final, and 33's = 1826
With 700r4, 3.42 final, and 33's = 1674
With 700r4, 3.08 final, and 33's = 1508

For 65MPH, locked TC:
With 700r4, 4.56 final, and 33" tires = 2113RPM
With 700r4, 4.10 final, and 33's = 1899
With 700r4, 3.73 final, and 33's = 1728
With 700r4, 3.42 final, and 33's = 1584
With 700r4, 3.08 final, and 33's = 1427

With the 6.2, the power band is from about 1600-2000RPM (and the efficiency band is roughly 1600-1800) . My suggestion of doing 3.73 is based on these numbers putting your truck in the lower end of the power band with a TC locked at 65, and the approximate middle when unlocked to allow for acceleration. You are still in the power band this way should you drive at 75 or 80 on some road where that is legal (i.e. the salt flats in Utah on highway 80). 3.42 might be too low as with the TC locked up, the cruise speed would put the engine below it's power band by almost 100RPM. 4.10's would be too short a gear as with the TC unlocked, you'd be already at the upper limit of the power band at 65, leaving less power for urgent acceleration to 70MPH.

Thus I stand by my opinion (and remember it's just that) being that 3.73 finals with a lockup TC in a 700R4 on 33" rubber is basically ideal for this engine for on-highway use.


LATE NOTE: For historical reference, the original TH400 3-speed with 3.08 final and 31's required the engine to spin at ~1950RPM at 55MPH (just inside the limit of the power band) - given that the federal highway speed limit was right about there in the '80s, and there was little reason to expect a truck to see anything vaguely resembling 80MPH, the gearing is just right for that set of engineering constraints. The D10 Blazer was also not expected to tow anything of significant weight with a towing limit of 3,000lbs total (3/4 ton - including the actual trailer's weight).