can the cummins survive? what size tire!

[kenmartin]

coming to a cross road and i wanted to see what your thoughts on this would be, a cummins 6bt, a th400 and a hummers stock gearing, trying to drive at least 60 mph!!! what size tires should make it happen? or do i just bite the bullet and put a computer controlled tranny in it which i hate!!!!!

[CumminsPower59]

BIG is all I can say, I have run countless M998's and M1151's over the years, I know that when blasting down the highway at 60mph in a M998, that little old 6.2 is crying for mercy. IIRC, they are goverened at 3600 no load, so I would bet that it's near that....

[BILTIT]

http://www.csgnetwork.com/multirpmcalc.html

Plug&Play


With 3.08 gears i would say 38's minimum.

[dazedandconfused]

Whats the gearing in that around 4.56 or lower?

Edit i googled and came up with axle ratios from 2.56-3.08.

[oldestof11]

And I do believe they have a 2.x:1 hub gearing too...

[CumminsPower59]

The diffs' in M998's are 2.73's and the hubs are 1.92's.

[dazedandconfused]

So that makes final drive 4.65 then right?

[CumminsPower59]

More like 5.24

[dazedandconfused]

Yeah i added instead of multiplied. Its been a ruff morning for me.

[BILTIT]

So either an OD trans or a gear vendors, both would be nice.

[CumminsPower59]

Gear vendors OD won't work with the stock fuel tank, there is only a few inches of clearance between the fuel tank and the drive shaft. On top of that, the rear drive shaft is only 28 inches long, so if you put an different fuel tank in the already small bed, and a GV on the back of the transfer case, the drive shaft would be just a few inches long.

[BILTIT]

They do sell a 90 degree adapter but i see the problem with the 28'' shaft. You can do a divorced GV setup, not sue if it helps any though.

[CumminsPower59]

The main deal with Hummer's/Humvee's in general is that the engine/trans combo sits further back in the chassis than normal vehicles. Most of what's under the hood is the cooling system, and the front four/six cylinders of the engine, which in itself is pretty small. These trucks were designed with alot of things in mind, ground clearance is one, therefore, space is comprimised and everything is crammed into a small area.

[simplysmn]

the Stupdest thing they ever did was drop a v8 diesel in the humvee the 6.2 is Scrap iron seen way too many blown up from just driving them normal

[Tacoclaw]

We're fighting this issue on our F550 that we swapped a 5.9 in for the 6.0. It has 4.88 or 5.38 gears in it and 70 is right at high idle. It will rattle the engine mount bolts right out of the block on a long trip down the interstate, as we learned on our first trip out to get a truck, so put loctite on all your motor mount bolts.

We're honestly debating on regearing it with a new 3rd member in the rear and dealing with the non-working speedo afterwards it's so bad. If gearing isn't a possibility I'd look into ways to smooth the thing out, like a better damper and possibly balancing the internals. The Cummins should be able to run all day at 3k since it's within it's governor, but who want's do listen to it and deal with the aftermath? We're kind of at a loss at what to do with this truck if the regearing doesn't pan out.