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Old 08-21-2006, 04:32 PM   #1
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1990 25' Airstream 250
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As my classic ages and the 454 tires, I have a dream of installing a duramax and a Allison 5 speed. Has anyone progressed beyond this point?

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Old 08-21-2006, 05:32 PM   #2
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Great idea, Dave. As a Duramax pickup owner, with 3 years and 40,000 miles under my belt, I think the Dmax/Allison would be a great combo for a motorhome. I am not sure of the logistics of such a repower, but it would be an interesting project. A place to start your research would be: if you have not already been there.

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Old 08-21-2006, 06:34 PM   #3
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Duramax, et al

There are a bunch of us (well, 3 or 4, maybe) who would spring for a diesel replacement for the 454 if we could find someone knowledgeable and competent to do the work. The usual reply I got when inquiring was: "it's too difficult, it's to hard, we won't." When you ask how many conversions they have done, the answer is ZERO.

It ain't brain surgery, but it does require experience and competence.

We will be interested if you find anyone interested in doing conversions.


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Old 08-21-2006, 06:39 PM   #4
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Thanks, thats an imazing web site. there is no question in my mind of the performance or the physical installation. I worry about the computers and elctronics of the newer engines - pretty sophisticated
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Old 08-21-2006, 06:45 PM   #5
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I suspect the way to go would be to purchase a wreck that the parts could be salvaged from. that way you would have all the black boxes, wireing looms, and computers to work with
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Old 08-21-2006, 07:36 PM   #6
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I have owned a Chev Silverado 2500HD ext. cab Duramax with 5 speed Allison since new in 2004. In my 39 years of towing with many tow vehicles I have nothing but good things to say about Duramax. The only bad comment-- what took them so long to build it? I can't put my finger on it but it seems to me that differential gear ratio and tire diameter are two factors you should research. I know that the computer monitors RPM and upshifts and downshifts the tranny to keep the RPM in the 1500 to 1800 range. In the pickups they only offer the 3.73 differential ratio with the Duramax. I don't know how the computer would react or rather if the shift points would be satisfactory with a higher axle ratio and larger tire diameter. I read your post and have responded with an off the cuff comment. I may be all wet but think you should look into this.
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Old 08-21-2006, 07:53 PM   #7
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It shouldn't be that difficult to do the swap. My buddy, a fellow engineer and Land Rover lover, put a GM 6.2 diesel into his '98 Land Rover Discovery. The horsepower is slightly down from the original V8, but the torque is WAY more than he had before. It's a very neat installation. And, the Rover's engine bay is TINY compared to the room you've got in your motor home. A Duramax should fit easily in your coach.

Any mechanic can swap in a 502 to replace your 454. Heck, you could put in a fuel injected 496 from a late model pickup. But, the swap to the diesel shouldn't be that big a deal either. You may have to change the rear end ratio; I'm not sure what you've got now. But I would think a 3.73 or 4.10 would be what you'd want. If you're already there, then you wouldn't have to mess with it.

You'll need a new radiator, new air box, new fuel pumps, etc. I'd echo the above comments in that I'd look for a wrecked donor vehicle and swipe all I could off it. But in the end, it wouldn't be that hard and you'd have a spectacular vehicle.

I myself was thinking of motorhomes just today. I watched "RV" last night. The 1948 Flxible Clipper that Jeff Daniels was driving was really sweet looking. I know many guys have repowered them. How cool would that be with a Cummins turbodiesel driving it? (Yes, I'm a Cummins fan )

Anyway, go for it. The Duramax with the Allison in your motorhome would be an absolutely superb setup! Heck, I'm starting to think maybe I should sell the Excella for an Airstream motorhome

Best of luck with it!!
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Old 08-21-2006, 07:58 PM   #8
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This is something I hate to say, Forget It!
The Duramax engine and Allison transmission combination requires a computer for the engine ECM and a Transmission control module TCM for the transmission, they talk to each other over a "CAN" bus. You can't just mate the two of them.
From what I understand it took the GM engineers 3 years to get them to work together, I guess the ECM and TCM programs are very complex.
I have also heard that trying to move the powertrain from a wreck to a new vehicle is almost impossible. Sorry.
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Old 08-21-2006, 08:20 PM   #9
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Why not look at a older 12 valve cummins 5.9. These motors have been used in MH's for many years the Cunmmins motor is also rated a medium duty motor as opposed to the Duramax rated light dutyIt also makes a lot more sense to put an in line 6 cyl. as opposed to a v-8. Not saying anthing wrong with the duramax just suggesting that with all of the retrofitting it might be easier to stay away from all of the computer interface and go for more mecanical. The Cummins is a proven 500,000 mile motor. Just a thought
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Old 08-21-2006, 08:38 PM   #10
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I picked up a 'Diesel Power' (?) magazine last month and there were several letters to the editor asking the same basic question. "Can I drop in a Duramax/Allison?" Sadly, they also stated that while not impossible, would be difficult. They mentioned the computer controller issues, but they also mentioned that the Allison is somewhat larger then the other trannies and to insert the Allison would require some delicate cutting and fitting.

BTW, to make matters worse, Allison came out with a 6 speed in '06. It growls nicely behind my Duramax making short work of the daily commute. I can't wait to stuff in a Bank's Six Gun performance package. Alas, that'll have to wait until I win the lottery.
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Old 08-21-2006, 09:24 PM   #11
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Airstream put an Izuzu diesel in many motorhomes just like yours. Why not check out a 454-Izuzu swap? Might not be a Duramax but maybe less expensive. I own a 02 Duramax with 80k and not a hint of trouble. Good Luck with you new engine whatever you do.
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Old 08-21-2006, 10:32 PM   #12
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All it takes is money

Call these guys and ask them where to start.
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Old 08-22-2006, 06:54 AM   #13
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I've heard the Duramax is somewhat an Isuzu already. Isuzu makes good engines, both gas and diesel. I'd think swapping in either an older Isuzu diesel as suggested or an in-line 6, 12 valve Cummins for simplicity.
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Old 08-22-2006, 08:27 AM   #14
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I have to agree with Gary. Unless you have unlimited funds and are extremely attached to you MH it would be extremely costly even if you found someone to do the work. My son who is a GM tech and shop foreman at a local Chev dealer pointed a few things out this morning over breakfast. If purchasing new the engine and trans alone would have a retail $$$$$ of close to $20K. Harness's and computers another $10K. The change also requires an instrument panel and harness as the range selector has to communicate with the trans. Like the range selecter there is no direct linkage for the throttle as its electronic throttle control. Not only does the cooling system have to be updated but an intercooler must be fitted. None of this takes in concideration of the fitment requirements of the engine and trans,exhaust system, complete fuel system change from tank to fuel lines to fuel cooling system. To compare this to a 454-6.2 diesel swap is like compareing grapes to watermelons. ----Pieman

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