gas milage of a cucv

[Barrman]

300 mile trip in the M1009 last week and 21.2 mpg. 62-63 mph on the open road and speed limit everywhere else.

 

[rhinob]

1985 M1009 with 33's (BFG AT"s), first 200 miles, city only driving.....15.3 mpg.

 

[67_C-30]

Okay, I am about a week away from getting my 1009 on the road, assuming all goses well. Here what I got, I installed a 700r4 with a B&m lockup mech. thingy,a turbo and alot of other crap. I was wondering what others with similar cofiguration have gotten concerning fuel milage?

I had a '84 K10 that had a 6.2/700R4/3.08 and it would do 23 - 23 in town and I got as good as 28 and once 29 on the highway. Your's will have the turbo, so I'm not sure how you will fare. I had a tach on that truck, and it hum along at 70 at only around 1700 RPM.

 

[tim292stro]

...so what's the average class?

639miles/45.8Gallons = 13.951965066MPG

What do I get?

Here's my M1028 records -...

...Won't paste well into the forums as it came out of a spreadsheet.

You can export as a CSV and paste the text.

 

[CUCVLOVER]

I guess I'll post in this old thread too.

I got 15-16.5 in the green machine, bringing it home from little rock, at 60mph most of the time.

But now I'm not sure what I get probably very little since I stand on the peddle a lot.
But I do know that pulling 4,000 ish lbs, at 55 ( took awhile to get to that speed) in a lot of hills on some back road i could almost see the fuel gauge fall.

 

[welpro222]

Im getting from 17-18 mixed driving with my m1008, but I have 3.73 gearing and 33 inch tires.

 

[rsh4364]

My 85 1009 3.08 gears 33" tires 20-22 mpg,The 86 1009 with 4.56 gears 33" tires 16.8 mpg.The 85 would see speeds of up to 70-75 mph,the 86 rarely sees 65 mph.The 86 recently got flowmaster super 44 2 1/2" mufflers and 2 1/2" tails so I expect mpg to go up a bit.My 85 has moroso 3" spiral flow mufflers and 3" tails and is really border line on noise,the 86 with the super 44s is perfect,very mellow idle,and very mellow at speed,but has a bit of a bark on acceleration.I will do a vid. soon.

 

[tim292stro]

I'm getting from 17-18 mixed driving with my M1008, but I have 3.73 gearing and 33 inch tires.

Original 400 3-speed or a 700 4-speed?

 

[tim292stro]

...the 86 1009 with 4.56 gears 33" tires 16.8 mpg...
...the 86 rarely sees 65 mph. The 86 recently got flowmaster super 44 2 1/2" mufflers and 2 1/2" tails so I expect mpg to go up a bit...

I'll be honest, I don't see the MPG changing more than 1MPG on long-term average with only an exhaust mod. If your 86 really has 4.56 finals then your engine would have to be spinning 3190 RPM at 65MPH. The max efficiency zone for the 6.2L is 1600-1800 RPM, above 2000RPM the efficiency drops rapidly. At sustained 3000+ I wouldn't expect the engine to last very long...

With 33" tires, changing the finals to 3.73 will drop the 65 speed down to 2600RPM roughly - swapping the transmission to a 700R4 (which has overdrive) and leaving the 4.56 would get your 65 speed down to 2110RPM. Doing both would get your 65 speed all the way down to 1730RPM, and IMHO is the real sweet spot for this engine. If you can couple that with a lock-up converter that kicks in in fourth under lighter throttle, your fuel efficiency could potentially see the mid to high 20's in MPG. Not bad for a truck with the aerodynamics of a brick.

I used the popular "GrimmJeeper's" gear ratio calculator for the numbers in this post.

 

[welpro222]

Originally Posted by welpro222
I'm getting from 17-18 mixed driving with my M1008, but I have 3.73 gearing and 33 inch tires.

Original 400 3-speed or a 700 4-speed?

Still have the 400

 

[tim292stro]

That perfectly lines up with my math mileage wise with that tire size an final ratio.

 

[welpro222]

I have a k20 6.2 with 4.10 and a 700r4 and its perfect all around for cruising and towing. I don't have much faith in the 700r4, but its held up fine. When I bought it, someone before me disabled the lockup function and made it so it flows fluid to the cooler full time. This works good for towing, because you do not want to stress the lockup system when towing. I wish I still had lockup for cruising with a disable switch for something.

I feel the 4.10 gearing is just about perfect for our 6.2 engines, even 4.56 gearing if you run bigger tires with a700r4 or if you have $ a 4l80.

 

[tim292stro]

...The max efficiency zone for the 6.2L is 1600-1800 RPM, above 2000RPM the efficiency drops rapidly...

Don't need to take a course at MIT to read lecture notes most of the time: http://ocw.mit.edu/courses/mechanic...on-fall-2006/lecture-notes/16diesel_contd.pdf

If you're planning on running in the 2-3K RPM range, get a turbo just to make sure you're not starving combustion of air...

 

[tim292stro]

I have a k20 6.2 with 4.10 and a 700r4 and its perfect all around for cruising and towing...

With the calculator assuming no-lockup, that works out to about 2000RPM at 65MPH with 33" tires. Pretty good. If you can get the lockup back that should drop about 100RPM to about 1900.

I wish I still had lockup for cruising with a disable switch for something...

They may have just cut the wire or unplugged the wire to the transmission. IIRC, the lockup solenoid has a pressure switch to detect 4th gear. You are also supposed to have the dual circuit brake light switch so that the lockup releases when you push the brakes. The circuit is supposed to go (from 12+ to ground): Battery+ --> fuse --> brake light switch --> 4th-gear pressure switch --> solenoid --> ground.

Adding a toggle switch labeled "lock-up inhibit" with "inhibit active=open (off)", "lockup available=closed (on)" between the fuse and the brake light switch would do just what you want.

 

[rsh4364]

I'll be honest, I don't see the MPG changing more than 1MPG on long-term average with only an exhaust mod. If your 86 really has 4.56 finals then your engine would have to be spinning 3190 RPM at 65MPH. The max efficiency zone for the 6.2L is 1600-1800 RPM, above 2000RPM the efficiency drops rapidly. At sustained 3000+ I wouldn't expect the engine to last very long...

With 33" tires, changing the finals to 3.73 will drop the 65 speed down to 2600RPM roughly - swapping the transmission to a 700R4 (which has overdrive) and leaving the 4.56 would get your 65 speed down to 2110RPM. Doing both would get your 65 speed all the way down to 1730RPM, and IMHO is the real sweet spot for this engine. If you can couple that with a lock-up converter that kicks in in fourth under lighter throttle, your fuel efficiency could potentially see the mid to high 20's in MPG. Not bad for a truck with the aerodynamics of a brick.

I used the popular "GrimmJeeper's" gear ratio calculator for the numbers in this post.

You were totally correct on your mpg prediction.Filled up today 340 miles 19 gals. fuel,but Im a bit heavy on the throttle because it sounds so good.I think I could get 19 mpg if I tried.My next low $ step is a 14x6 aircleaner and fresh air intake.Then regear to 3.73s or 3.90s.And then finally a 700r4 trans.conversion.After that turbo set up or maybe a set of Stans headers,just because I cant really find any reviews on them,seems like everyone wants to try them but nobody does.And yes you are correct at 65mph Im running nearly 3200 rpm,which I hate, and generally try to stay at 60 mph or less.I really don't like running a 6.2 above 2500 rpm.But at 2500 with this one Im only running about 54 mph.Thanks for your advice,and isn't it totally amazing these outdated trucks are capable of 22mpg and are so easy to work on after some learning.I think I have my soon retiring Dad talked into a cucv.

 

[tim292stro]

You were totally correct on your mpg prediction.Filled up today 340 miles 19 gals...

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

...My next low $ step is a 14x6 aircleaner and fresh air intake. Then regear to 3.73s or 3.90s. And then finally a 700r4 trans conversion. After that turbo setup or maybe a set of Stans headers...

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....

...and isn't it totally amazing these outdated trucks are capable of 22mpg and are so easy to work on after some learning...

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.

 

[tim292stro]

I should mention that if you did a ram-air mod now with a less restrictive filter you may see another MPG or two assuming you do a lot of highway driving. There is a punch-out in the core support below the NATO plug that was meant for this on Gassers (like the 454 powered Crew Cab I'm converting to a Cummins diesel). The front grille is a good high pressure zone to intake air from - again due to the general lack of aerodynamic qualities. I believe the Banks Sidewinder Turbo Kit puts a BHAF under the hood, it would be better served IMHO with a Donaldson PowerCore filter (<$100) ducted to the ram air opening especially since that kit does not use an intercooler.

 

[welpro222]

In response to tim292stro's post above.

They may have just cut the wire or unplugged the wire to the transmission. IIRC, the lockup solenoid has a pressure switch to detect 4th gear. You are also supposed to have the dual circuit brake light switch so that the lockup releases when you push the brakes. The circuit is supposed to go (from 12+ to ground): Battery+ --> fuse --> brake light switch --> 4th-gear pressure switch --> solenoid --> ground.

Adding a toggle switch labeled "lock-up inhibit" with "inhibit active=open (off)", "lockup available=closed (on)" between the fuse and the brake light switch would do just what you want.

The previous owner had the lockup solenoid removed from inside the tranny.

 

[tim292stro]

That sux

It would be worth it for cruising fuel economy to put that back in if the TC is a lockup version. If the TC is a non-lockup, that might explain why they took it out. Lockup converters get a bad rap if they don't have enough friction packs in them (happens on consumer diesels too often in my experience) - this causes them to slip and burn up.

 

[welpro222]

I'll probably just worry about it when the tranny goes south and I get it rebuilt.