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Frankenstein Did you put a 6.5 in a Camaro? A Duramax in a boat? A Cummins in a Chevy? A Powerstroke in a van? Then you must have a touch of the good Dr. Frankenstein. Post your stories, questions, discussions in here... this is intended to be a place to discuss your questions on how to, what to do, etc...

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Old 09-22-2015, 11:32 PM   #1 (permalink)
calsdad
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Contemplating a Suburban Project - Should I do it?

I've spent quite a bit of time here in the past because I started thinking seriously about going the Duramax into a Suburban route.

Right now I've got a 2003 2500 6.0L Suburban - but I think it's time in my life is growing short. I've spent the last month trying to track down some serious running problems - and it's also got a lot of rust issues (New England).

The wife is sort of pushing me to think about replacing it - so I think I could green-light getting a newer one without much trouble.

Plus - I really prefer the GMT900 generation Suburban / Yukons over the GMT800's I think.

I think I would go Duramax - but for one thing: I spent a LOT of time investigating the legality of putting a diesel into a Suburban here in MA - and the general consensus is that it's pretty much a no-go, unless I want to risk running afoul of the emissions Gestapo.

My goals for a replacement for my current truck would be:

- Get into a GMT900 gen truck - Suburban or Yukon. I like the idea of doing a front end swap for a Silverado front end just to make it a little more distinctive

- Start with a truck from a non-rust area , and then spend some time going anal on the rustproofing, with the goal being to fortify the truck to last a couple of decades in New England winters without turning into a rust bucket. I have done a number of car restorations and become a semi serious student of rust, I think I know how to do this and have it work.

- More power. This is where I'm looking for advice from the brain trust here. I had a guy (who's a service manager in a GM dealership) over here today helping me get my 2003 running - and we were talking about the different trucks - and he made statement that really got me thinking. I had always thought the 8.1L engines were total gas hogs. He said the 8.1's in his experience - were no worse than the 6.0L engines - especially when towing heavy loads.

So that got me thinking.

What's the do-ability of swapping an 8.1L engine into say a 2007 or 2008 Suburban - and put a 6 speed Allison behind it? My understanding is that the 8.1L really works better with an Allison behind it. The Allison doesn't normally fit into the Sub chassis - but I could just jack the body like has to be done for a Duramax install.

I'm thinking if the tunes can be made to get a Duramax to workin the Suburban chassis with the dual tank setup and Allison - then a tune should be able to be put together for an 8.1L with a 6 speed Allison - in the Suburban chassis.

I'm thinking of a 2007 or 2008 truck because I figure the electrics should be more compatible with the 8.1L - compared to the later trucks (there was an electrical control change - wasn't there?)

Sorry it's not a diesel conversion question. But this might be the best I can do. A gas engine to gas engine conversion I don't think would raise any eyebrows if it was done correctly.

Thanks in advance for any help!

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Old 09-23-2015, 03:29 PM   #2 (permalink)
Fordiesel
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What do you plan to use the new to you Suburban for?

How did you use your current Suburban?

Real world usage is a better metric to guide your decision over the innate desire to have a Suburban with the most power capable of doing, hauling, or towing anything. Because they can't. The 3/4 ton Suburban frame in the GMT800 is only 1/2 to as little as 1/3 the thickness (in some areas of the frame) as the GMT400 it replaced. The GMT900 has the same frame as the GMT800 (in the 3/4 ton Suburban only, the 1/2 tons had more changes).

A paper thin frame is only capable of handling so much tongue weight cantilevered some 4 to 5 feet aft of the rear axle. And with the Suburban, that is usually the only place that weight beyond the GVWR of the vehicle is usually placed. If the Suburban is for the most part a daily driver, with only occasional usage towing, then converting it to a different engine, of any kind, may not be worth the cost or the hassles of working out the kinks of the engine change, let alone the hurdles of emissions inspections.

On the other hand, if the main reason for getting and setting up the Suburban is to take more than four passengers on a camping trip with a 30 foot tag trailer in tow, then the powertrain upgrade makes more sense... but...

Since you are getting a new to you GMT900 body style, there are a few other things to look at as far as power to the ground is concerned.

First and foremost is axle ratio. I'm not sure if GM still offered the 4.10 ratio in the 900 Suburban, but if they did, then I would hold out for it, because it will make all the other gears in the transmission more effective in their range, before you reach cruising speed, especially when towing up hill.

Second, at some point in the 900 series, GM started installing 6 speed transmissions. That gives two more gears right there, and again, more usable hill climbing prowess. The 6L90 is no match to the Allison 6 speed, and some would argue that a built 4L85e is actually stronger, and "drives" better by having a larger rpm range within each gear, for less hunting and shifting. But as far as fuel economy is concerned, all the shift management of the 6L90 does manage to work in eeking out a couple more mpgs in the city, where it is most difficult to get gains.

Third, because of that six speed transmission, one wouldn't expect you to be mating that with the 8.1, due to the control electronics. However, since the 6 speed does mate up to Gen IV small blocks, there might be an opportunity there for you to hop up a 6.0L block with 6.2L heads, flat top pistons, an RV cam, and you can build up a 400+HP, 450+TQ powerplant that looks essentially bone stock small block to the gestapo.

There are 100 times more parts (both aftermarket and OEM) available for the small block than for the 8.1L, which hasn't been made in 6 years. Even when the 8.1L was being made, the production line was very low volume, and had to be idled from time to time until the final day... December 18, 2009 (the month "L", the twelfth letter in the alphabet, the day 18, that matches the GM 8.1L RPO code L18).

These are all things I would consider. I think a better case can be made for repowering a Suburban with a D/A than with an L18. If you are still thinking about it, pay a visit to performance trucks dot net. The same question comes up from time to time, and all of the experienced gas engine experts over there seem to concur that a built up small block (from a cam and a program in an L92 to a fully blown LSX or LSA) would offer equivalent power and easier integration with the electronics than an 8.1L would.

The foregoing comments are not from personal experience. They are just an amalgam of my own investigation from having the same thoughts as you a while back.

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Old 09-23-2015, 11:03 PM   #3 (permalink)
calsdad
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The reason I have a Suburban - and wish to keep having one , is because to me - it's a "do all" vehicle. I fill it up with people on occasion. I like the ability to put a 4x8 sheet of plywood in the rear. I like the fact that I can shove a 16 ft long piece of lumber thru the truck and have it stick just a few feet out the back window. It fits in my garage. And every now and then I tow an 8000-10000 pound trailer with it. The 6.0L is hard pressed with a heav trailer - which from what I've read - the Duramax, or an 8.1L , would not be.

I've spent quite a bit of time here going thru the Duramax conversions that have been done by numerous people here - and the ones done by Duraburb.

If I had the ability to do it - I would very likely go the Duramax into the Suburban route. The diesel gives good gas mileage - and substantially increases the towing capabilities of the Suburban. But I've talked with Duraburb, I've gone back and forth with a guy from the State Dept of Environmental Protection - and I've asked around some of the people who have done the conversion in this state. What I've found is that they either did the conversion on trucks that are more than 15 years old - or they take their truck to a "friend" to get the yearly inspection. That's not the road I want to go. Unfortunately the Duramax conversion is pretty much out as far as I am concerned.

If there's an actual problem with the frame on these towing 10-12,000 pound loads - I've yet to hear about it. The biggest problem I've read about vis-a-vis the GMT800 and GMT900 Suburbans is that the factory trailer hitch is a sort of a piece of junk - and anybody who is serious about towing should invest in a much better hitch.

My problem is pretty simple: I actually spent a LOT of time investigating the "legality" of putting a Duramax into a Suburban and being able to live with it without running afoul of the inspection process. 8600 GVWR trucks do not get emissions inspections here - at least not up to the 2009 model year. So technically it's possible to dump a diesel in a Sub - and get away with it - but a diesel engine is not a gas engine - and it would pretty obvious to anybody who has even a smidgen of an idea that the engine was non- standard.

Putting an 8.1L in there though - would be all but invisible to anybody but the most astute mechanics. Especially because - if what I've read in a few other truck forums is true - the same computer can be used to control the 8.1L - as the 6.0L.

I'm asking about the 8.L / Allison combo - because in other trucks - where it would fit - that combination supposedly worked very well, and the 8.1L was detuned somewhat so that the 4L85 would live behind it. A similar method (raising the body ) - could be used to put an Allison behind an 8.1 - as is used in the Duramax conversions.

I know this whole thing can be made to physically fit into either a GMT800 or a GMT900 Suburban/Yukon. I think my main questions would revolve around the electronics. I'm thinking similar custom work would have to be done as is done with the Duramax conversion - to get the 8.1L / Allison combo working in the GMT900.

Last edited by calsdad; 09-23-2015 at 11:06 PM.
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Old 09-24-2015, 12:46 AM   #4 (permalink)
blackart
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Quote:
Originally Posted by calsdad View Post
....I'm asking about the 8.L / Allison combo - because in other trucks - where it would fit - that combination supposedly worked very well, and the 8.1L was detuned somewhat so that the 4L85 would live behind it. A similar method (raising the body ) - could be used to put an Allison behind an 8.1 - as is used in the Duramax conversions.
I can speak freely on this subject because....I don't know a damn thing about it. But, my understanding has been (for some time) that the reason for the body lift on Duramax\Suburban conversions was to allow for clearance of the radiator (LBZ) not the Allison. Maybe I'm wrong...

I think every GMT 800 Silverado with a 8.1 I ever saw had a five speed Allison behind it. For a long time I began to believe that was the only way they were made (it's not). Seven or eight years ago I met a guy that had transplanted the 8.1 & Allison from his wrecked Silverado into his wife's Suburban. He hadn't gotten the memo about the Allison not fitting, so he just went ahead with the swap like it was no big deal. He seemed surprised when I asked if the Allison put up a fight going under the floorboard (why shouldn't it fit?). He was not any super savvy tech, just a careful and methodical hobbyist parts changer. Now I have no idea whether any of this translates to the GMT 900 platform, you're on your own there. If it were me doing it though, I would go with the diesel.
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Old 09-24-2015, 06:06 AM   #5 (permalink)
calsdad
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Quote:
Originally Posted by blackart View Post
I can speak freely on this subject because....I don't know a damn thing about it. But, my understanding has been (for some time) that the reason for the body lift on Duramax\Suburban conversions was to allow for clearance of the radiator (LBZ) not the Allison. Maybe I'm wrong...

I think every GMT 800 Silverado with a 8.1 I ever saw had a five speed Allison behind it. For a long time I began to believe that was the only way they were made (it's not). Seven or eight years ago I met a guy that had transplanted the 8.1 & Allison from his wrecked Silverado into his wife's Suburban. He hadn't gotten the memo about the Allison not fitting, so he just went ahead with the swap like it was no big deal. He seemed surprised when I asked if the Allison put up a fight going under the floorboard (why shouldn't it fit?). He was not any super savvy tech, just a careful and methodical hobbyist parts changer. Now I have no idea whether any of this translates to the GMT 900 platform, you're on your own there. If it were me doing it though, I would go with the diesel.

That's exactly the reason for the body lift on the Suburban/Yukons that get the Duramax conversion - there needs to be clearance for the Allison transmission.

My understanding is that in the Suburban / Yukon - the 4L85E was used - for just this reason: the Allison would not fit. I've also read in a number of places - that the 8.1L was detuned somewhat in the SUV's because it was hooked up to the 4L85E. Additionally: I've read a number of accounts of people with the 8.1L/Allison combo either in Silverados or other pickup-chassis trucks who thought it made a great tow vehicle and had a bunch of power.

I guess I need to say it again: The Duramax combo for me is pretty much a NO-GO. I would REALLY like to do it - but I've spent a LOT of time investigating exactly what I have to do to do it legitimately - and the answer keeps coming back : you can't. The only way to really do it, is to either get a 15 year or older truck (no emissions consideration whatsoever) - or to just go ahead and do it on a newer truck - and find a friendly inspector - and hope he's going to be there for as many years as it takes to get past the 15 year mark.

I don't want a 15 year old truck - my 12 year old truck already has enough issues. I want a NEWER one.

What I'm saying is this: This swap should pretty much mimic the Duramax / Allison swap. I'll have to lift the body the same way it would be for the Duramax swap. Mechanically - I'm like 99.9% certain this is do-able. I think the main technical sticking point is: Could the engine controls be adapted to the 8.1L/Allison combo the same way they are with the Duramax/Allison combo
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Old 09-24-2015, 05:00 PM   #6 (permalink)
blackart
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Quote:
Originally Posted by calsdad View Post
That's exactly the reason for the body lift on the Suburban/Yukons that get the Duramax conversion - there needs to be clearance for the Allison transmission...
At least one Worthy on this board begs to differ with you....
https://www.dieselplace.com/forum/63-...ml#post5194914

I have seen it mentioned more than once that an Allison will go under a GMT 800 easier than a GMT 400.... And since a GMT 900 is expected to accept a 6L90E, and since one of those is darn near as big as an Allison...
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Old 09-24-2015, 10:56 PM   #7 (permalink)
calsdad
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Quote:
Originally Posted by blackart View Post
At least one Worthy on this board begs to differ with you....
https://www.dieselplace.com/forum/63-...ml#post5194914

I have seen it mentioned more than once that an Allison will go under a GMT 800 easier than a GMT 400.... And since a GMT 900 is expected to accept a 6L90E, and since one of those is darn near as big as an Allison...
I'm referring to either a GMT800 generation SUV - or the later GMT900 SUV's.

Go read thru the Frankenstein forum here on Dieselplace - I haven't seen a Duramax/Allison conversion into either the 800 or 900's yet that didn't have to do a body lift to accomodate the Allison.

The reason why the 8.1L engines in the GMT800 Suburban/Yukon's came thru with the 4L85E transmissions - is because the Allison would not fit.
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Old 09-25-2015, 02:24 AM   #8 (permalink)
blackart
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Quote:
Originally Posted by calsdad View Post
...Go read thru the Frankenstein forum here on Dieselplace - I haven't seen a Duramax/Allison conversion into either the 800 or 900's yet that didn't have to do a body lift to accomodate the Allison...
The Frankenstein forum - of course -Why didn't I think of that? Thanks for the tip. Know what? There's this guy that posts a lot on the Frankenstein forum called theTDIguy. He seems to know a bunch about these Duramax/Allison conversions. Here is what he says:

https://www.dieselplace.com/forum/4052528-post69.html
and
https://www.dieselplace.com/forum/4548583-post5.html
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Old 09-25-2015, 09:39 AM   #9 (permalink)
elcaminonut69
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The Suburban Club Member

I'm curious about why you're worried about an inspection if the truck is exempt because of the gvw. Do you still have to have an inspection less emissions?


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Old 09-25-2015, 10:27 AM   #10 (permalink)
boisebiker
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blackart is correct, all of the 2" body lifting is so that the radiator and fan shroud line up with the fan on the duramax. Most guys now do a "reverse rake" to level out the body since most 2500 series have a stink bug looking body line.

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