M1008 Safe Speed versus M1009

[swiss]

My understanding is that the safe "engine" speed for the M1008 is lower than M1009 and lets assume all stock rear end, tire size etc. Given that both vehicles share the same 6.2 and transmission I am assuming the difference is the rear end gear on the M1008 turning the 6.2 at a higher rpm at the same speed as the M1009.

Assumptions: Stock Equipment

Questions:
1.) Is rear end gear different between the M1009 and M1008?
2.) Is the standard tire size different?
3.) What would M1009 owners consider a top "safe" speed.
4.) What is max RPM for sustained running that you should be driving at.

I see alot of discussions on top speed and rpms talked about on the M1008 but not as much on the M1009.

I really need to hook up a tiny tach

 

[Varyag]

1009 = 3.08
1008 = 4.56

 

[jeeplvr247]

When I am on the expressway I like to run my 1009 at about 60. I know it will go faster but it makes quite the difference in fuel economy. If you run it at 60 you will never have to fill the tank!

 

[Reverend Evil]

M1008 the tm and the stickers on the dash say 55 mph. as for the rpm not sure what she is running need to order me one of those tiny tachs but i also know 4'' lift and 37s the county was nice enough to put out there speed sign and at 55 on the dash with 37s its 67 and with my phones gps it is about 10 off after 30mph. but i wouldnt push it past 55 on the dash as mentioned before over 50 in a 1008 the fuel goes faster than the truck

 

[Bob H]

redline on a GM 6.2 is 3600
60 mph is about 2100 rpm in a M1009
and 70 is about 2500 rpm

while 55 in a M1008 would be nearly 2900 rpm.

 

[chevyCUCV]

I like going 65 in my m1008. The engine is not going over rev.

The only thing hurting from high speeds is the fuel tank, and my ears.

 

[jeeplvr247]

The only thing hurting from high speeds is the fuel tank, and my ears.

I can't help but notice you have a '08 with a blown engine...just sayin'

 

[tom2147]

I blew a front tire going 55 while recovering my M1008, the pucker factor was bad enough at that speed on a busy interstate!!

 

[91W350]

I like going 65 in my m1008. The engine is not going over rev.

The only thing hurting from high speeds is the fuel tank, and my ears.

Your math is very bad, the engine was designed to run around 1800 to 2200 rpm. They left the governors open to get decent pulling out of the wide spread in transmission ratios. They never intended for the engines to run on the governor like a lot of engines can. They were built as a fuel economy engine, not a full service work diesel. The trucks they really shined in were high geared 2 wheel drive pickups and Suburbans. School districts all across the country learned quickly that mileage figures on the highway with a Suburban full of students, was in the mid to upper 20's. The crafts people and bass boat pullers loved them. The guys who bought 4.10 one ton dually pickups to pull their race cars with, hated them. In low rpm applications they ran longer than the trucks wrapped around them. In high rpm applications they cracked the main bearing webbing and threw rods. Running a M1008 with a 32" tire 65 mph puts you over 3,000 rpm. You might get away with it for a year, maybe two years, maybe until the end of the week or tomorrow. A lot of guys consider them throw away engines, if you are one of those guys, by all means, drive 65, heck go for the gusto and drive 70. Glen

 

[chevyCUCV]

I can't help but notice you have a '08 with a blown engine...just sayin'

Haha thats funny
But that truck has never been registered by me, i never drove it. Came that way from a p.o.
And there are lots of civi vehicles with 6.2 diesels that are used on freeways like campers and some bread/box trucks.

Also i rarely drive highway so, im not worried about the engine's life.(besides it being a 6.2)

 

[swiss]

Okay going to the next step, assuming the following I am using a web calculator to get the safe speed at 2800 RPM

Engine Speed RPM 2800
Transmission Gear Ratio 1:1 in third gear
Differential Gear Ratio 3.08
Loaded Tire Radius inch 15 inches (I did not measure yet the truck is in the woods)

The calculated speed would be 81.7 mph.

If I assume some loss from heat, friction etc it would seem you can run 75 and be at 2800 rpm which would be at roughly 75% of redline.

Am I missing something here?

 

[kipman]

That seems correct, but you will use about 25% more fuel, I run my 1009 at 60 and get low 20s MPG.

 

[swiss]

As far as gas milage I am getting 15 mpg running on the highway between 68-75 and towing my M101 about 15% of the time. I know alot of guys are talking 20 mpg but that could be at speeds below 65 mpg. I am going to try testing a tank by driving slower.

Taking this one step further then, the taller tire while providing less torque would allow for a faster speed and lower RPM's. If I ran 32's as the tire size, then theortically I could get at 75 mph and be at around 2600 rpm. That would be a nice win win on highway performance and engine life. They drive fast down here in Georgia

 

[Cleptomaniac]

I have 35s on my 1009 and the gear ratio is a bad combo. I think if you had the 35" tires in a highway tread(mine are snow and mud) it would be a lot better. Their is not enough hp/tork to maintain 70+ speed with the current set up.

 

[jeeplvr247]

IF you slow it down you will save a lot on fuel. I do about 60 on the highway and get mpg in the mid-20s

 

[jaymcb]

SO it sounds like 32's are a good bet for running down the highway, but not so bad it won't climb a hill. Do the 32's need much bigger rims or much of a lift to fit?

 

[91W350]

No rim or lift for 32 11.50 15s.

 

[swiss]

From my research on Steel Soldiers the following are the largest tires without a lift or rubbing issues if your leaf springs are good:

Largest to Smallest
1.) 33x12.5x15, if you use the BFG KM2 it might rub a bit on turn,
2.) 33x10.5x15, same tire just thinner
3.) 32x11.5x15,
4.) 31x105x15 (Original Sized Tire for M1009 CUCV)

I am looking at BFG Mud Terrain KM2 so diameters are as follows:

33 = 32.8"
32 = 31.8
31 = 30.8

 

[jaymcb]

do the narrower 33x10.5x15 also rub, or is the rub caused by height?

 

[swiss]

Jaymcb

My understanding is that the 12.5 rubs with aggressive tread on the side of the inner fender well when aggressively turning. There was a post I reviewed yesterday that showed with the 12.5 rubbing that was aliviated by bending in the inner part of the fender on the side. I did check with another ss member who is running 33x12.5 AT treads not the KM2 threads and he said there is no problems.

Looking at the pictures yesterday from the post the 10.5 would not cause a problem with an aggressive tread.

Steve