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Hummer Knowledge Base

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Swapping Engines to a Cummins 5.9L:

The Cummins 5.9B will in fact fit the Hummer, but only after a substantial amount of work. The cooling stack needs a bit of modification, and the entire hood needs about an 2 inch raise down the center. We cut off the raised center section of the hood, added a bit of cored fiberglass and put everything back together. NOT for the faint of heart or non mechanically inclined. Your not going to pull this swap off in your driveway. The 5.9 we installed was dynoed at above 300 HP with a few quick tweaks. Torque was on the order of 600 ft lbs.. If you do pull a swap like this off, plan on upgrading the rest of the driveline with some seriously improved parts.

We mated the 5.9 to the highly regarded Allison 545 auto. This is commonly used in commercial fleets, schoolbusses, etc and is virtually indestructible. Torque inputs of 1000 + ft/lbs. are nothing to worry. The Allison also has some nice nifty features like a Power Take off. We drove a 24GPM pump off this to power the front winch. For those of you interested the 545 WILL fit the Hummer tunnel, and only requires a bit of crossmember modifications. Oh, and plan of finding a new place for the fuel tank. (we placed it in front of the rear bumper (like the aux tank setup) and used the new found room for our hydraulic tank. Finally, gut the factory transmission cooler, as it is vastly undersized. Before the question is asked, I cannot verify if the 545 will bolt to the GM diesel, so I'm not sure how useful it will be as a replacement trans.

Additionally the 545 will not bolt to the 242 transfercase without some serious machine work (Again from memory). We went the NP203 route which in itself is a pretty beefy gear driven piece. I'm assuming a 205 would also drop in, offering a two wheel drive mode. At this point is necessary to lengthen/shorten the driveshafts and such. Probably the easiest part of the whole swap as we farmed it out. Finally, the factory halfshafts (old style, as this was a 93 truck) looked awfully puny, so we made up our first set of high performance halfshafts. (4340 steel, special heat treat, etc etc etc)

All said and done, probably close to $30K invested and a few solid weeks of fabrication. Not for the faint of heart at all. Truck ran/runs like a champ. Dont have acceleration figures or anything like that, but it goes without saying this thing is a monster. Cooling was not a problem on straight water and water wetter and a custom aluminum radiator. The truck is still parked not more than 200 feet from where I'm typing, and is used as a test bed / "abuse it till the part in question breaks". It's accumulated about 15-20 K miles since the swap and there has yet to be a driveline problem.

Would I recommend this swap to the average DIY'er? .... NOT A CHANCE

Would I do this again for myself? Even then the answer is probably NO. This mod just costs way too much, and for the same cash (and some of Peninsular Diesels Goodies) you can get yourself into a well built 6.5 with all sorts of driveline upgrades and a few years fuel costs to boot.


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