Lil Red - Duramax 6600/Allison 1000 Conversion & OBS/NBS Dash Conversion

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This image shows more detail about how the intercooler end-tanks were modified. The intercooler's inlet and outlet were moved outward to clear the boxed steel sections of the radiator core support, and then the end-tanks were modified to help provide more clearance for the head/park lamp assemblies. A 4" hole needs to be cut in the radiator core support where the intercooler's inlet/outlet pass through.

I made all of the cuts/mods to the original intercooler, then took it and the various pieces to a metal shop for aluminum TIG welding. If doing this again I'd buy my own TIG welder and learn how to use it. In the end there would be no labor charges and I'd still have the TIG welder... all for about the same final cost. And incidentally, once all of the mods were completed I flushed water through the intercooler in each direction several times in an effort to remove any debris that might have collected internally during the process of modification.

I used the GM factory intercooler hoses, clamps and aluminum tubing produced for a 2001 model year Chevy/GMC equipped with a Duramax 6600. If you have a donor vehicle that'll provide all this, you're golden. You don't have to use the original factory parts, but they will make it just a bit easier. The factory aluminum intercooler tubing will need to be extended because of the widening of the intercooler inlet/outlets. This is a relatively easy process. I used 3" aluminum agricultural sprinkler pipe to provide the extension material. I still have about ~8' of this pipe laying around... if anyone needs some. The Conversion Guide shows how/where to add the extensions.

Of course, there are alternatives with regard to intercoolers. You could search for a generic intercooler core from an online source that suits your installation, then modify it as/if required. We did that very thing for a 6.5L diesel Suburban in a book published by The Diesel Page a few years ago... see link. At the time, the total cost, which included the core, all of the hoses, clamps and aluminum tubing cost about $400 total. So, you don't have to begin with a Dodge or GM intercooler. A generic intercooler core just needs to be sized for a diesel engine approximating the displacement of the Duramax, and of course fit into the available space.

In addition, I know of at least one Duramax conversion running without an intercooler. An owner in Canada used our mounts and Conversion Guide, but chose to avoid the installation of an intercooler because his use for the truck would be mostly light-duty. Personally, I'd still want an intercooler because of the ~20-psi boost pressures and the heat load that creates, but the installation in that Canadian truck shows that a conversion can work without an intercooler in certain light-duty situations. It should be noted that running without an intercooler while towing heavy could result in dangerously high EGTs and engine damage.

How is the intercooler mounted, you might ask... The intercooler shown here is setting on 3/16" thick rubber strips that had been glued onto the radiator core support using silicone caulking - to the horizontal and vertical surfaces where the intercooler core made contact. You can see small portions of the strips I'm talking about in the above image. The modified hood latch assembly then clamps the intercooler to the radiator core support - using rubber strips as cushioning. It's been a successful and solid mounting strategy for a long time... although, if my truck were driven on lots of rough road/off highway use, I'd consider welding some beefy 1/4" thick aluminum mounting tabs onto the intercooler core end-tanks that allow bolting it to the radiator core support using rubber-isolated hardware - along with the rubber cushioning strips mentioned here.

There are always different ways to "skin a cat". You may have a different way. If nothing else, what's shown here is simply one way, albeit a successful way, that describes how I installed an intercooler in my truck - performance, reliability, cost, reproducibility and of course appearance, are all important factors.

Beyond the intercooler - there is another related conversion hurdle I faced soon after completing the intercooler installation, and I may show that solution here in a future update... the A/C condenser installation. I'm really happy with the modified A/C condenser I installed - it's solid, reliable, works great and looks professional. After the initial installation of the A/C system and R-134A charge, it's not needed any attention in the years since. Let me know if you'd like to see more. --- Jim

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