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Old 11-29-2018, 07:56 AM   #1
Mini-Skoolie
 
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Big block GMC 366,427,500

Does anyone know if the transmissions to any of these engines would bolt up to a Duramax. I was looking at a nice bus with a 5spd. and a split rear end but it has a 366 gas. I would like to change it to a Duramax or a earlier gm diesel. Or should I just look at a different bus, I kinda like the 5spd and split rear. And that is the only one I have seen in a while.
Thanks for the input.
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Old 11-29-2018, 08:17 AM   #2
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2 things.

Firstly, yes, the bolt pattern on the back of a 366/427 medium duty engine is still the same as any other gmc v8. The ones that I saw would use an adapter ring to turn the gm pattern to an sae pattern to mate the medium duty transmission to the engine.

Secondly, check your gear ratios with that engine/trans. From what I've seen, all of the 2 speed rears installed behind gas engines usually have gear ratios in the 800's for low and 500's for high. They also would likely have used a direct 5th trans. With those gas engines they needed all the mechanical advantage possible to get moving.

If you're using a duramax, you won't need the low speed in the rear axle, and you'll be disappointed by your top speed in high gear with no OD.

I'd look at a different bus.
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Old 11-29-2018, 09:30 AM   #3
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I've played with the Caddy 500 family of engines a bit (368/425/472/500). Their bolt pattern is the same as the Buick/Olds/Pontiac, but not the Chevy/GMC. The stock torque of the 500 is around 365 ft lbs for the later 190hp versions. The earlier versions have higher compression so are rated higher. I'd bet there are adaptor kits for them.

Dave
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Old 11-29-2018, 10:11 AM   #4
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I built a mean arse 425 years ago... the 425's and 500s were available as Multi-point EFI engines (yes my 76 cadi 500 was EFI factory as was my 425 thaty came from a wrecked donor car).. this 425 ended up going intp an 81 fleetwood brougham project..



the significant thing about the factory EFI cadi's was the manifold has injector holes.. 8 of them.. and the injector holes will hold TPI style injectors... so the possibilities of build up and tune are nearly endless...



back to the Duramaxx.. if you can get a duraaxx to bolt into a school bus.. i would take the allison 1000 from the duramaxx with it.. esp if its a 6 speed.. thats a nice highway combo. and fully tuneable with EFIlive..
-Christopher
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Old 11-29-2018, 04:01 PM   #5
Mini-Skoolie
 
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Thanks guys I'll have to look into the rear end gearing. And it's a five speed stick not a six.
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Old 11-29-2018, 11:12 PM   #6
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I would say find another bus and don't try to swap a Duramax into a bus that currently has a gas engine in it.

You might be able to get everything to bolt up. One of the real challenges would be to get a flywheel and clutch that would work on the Duramax.

But as it was pointed out above, the gearing is not going to work very well for you.

The big block GM engines in medium duty trucks and buses had a redline between 3500 and 4000 RPM. Some went even higher. A Duramax is going to redline at a much, much lower RPM. Much more like the Cummins ISB/ISC and IHC DT466 that have a redline in the 2600-2800 RPM range.

If the bus tached out at 60 MPH with the gas engine it is going to tach out with the diesel somewhere around 45 MPH.

With enough time and $$$ just about anything can be done. But swapping a diesel engine into a bus that currently has a gas engine is not going to be an easy swap. It isn't going to be a simple matter of unbolting one engine and bolting another one in it's place.
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Old 11-30-2018, 09:47 PM   #7
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Quote:
Originally Posted by Booyah45828 View Post
2 things.

1Firstly, yes, the bolt pattern on the back of a 366/427 medium duty engine is still the same as any other gmc v8. The ones that I saw would use an adapter ring to turn the gm pattern to an sae pattern to mate the medium duty transmission to the engine.
......
I'd look at a different bus.
Quote:
Originally Posted by cowlitzcoach View Post
I would say find another bus and don't try to swap a Duramax into a bus that currently has a gas engine in it.
.......
If the bus tached out at 60 MPH with the gas engine it is going to tach out with the diesel somewhere around 45 MPH.
......

1 Yes the block pattern is the same on those BBC and duramax. The REALLY bad news about the adapter for the SAE large clutch is that they are usually part of the rear motor mount so you can't just remove them.
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Old 11-30-2018, 11:25 PM   #8
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Leave it gas and put a new gm performance engine with electronic control and fuel system. You'd be impressed with what the new gas engines can do, and get decent mileage. All of your accessories should bolt up, or be able to with new or used brackets. It would be a straight forward swap.
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Old 12-01-2018, 09:07 AM   #9
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Quote:
Originally Posted by Mekanic View Post
1 Yes the block pattern is the same on those BBC and duramax. The REALLY bad news about the adapter for the SAE large clutch is that they are usually part of the rear motor mount so you can't just remove them.

The one I saw in the junkyard was like an inch thick cast iron. As far as the engine mounts were concerned it was the standard v8 style with 1 on each v and one on the transmission.
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Old 12-01-2018, 09:28 AM   #10
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booyah has it right.. on the allison 1000s in duramaxx applications the trans requires a cross member at the tail shaft the rear motor mount is not part of the housing like on medium duty / heavy duty applications.. you would need to fiund an SAE3 housing from like a 4500 / 5500 which would allow you any SAE3 transmission.. im not sure if an SAE2 was ever made for the duramaxx or not.. the way I believe is that the chevy V-8 bolt pattern from all of them match. so it may be possible to find medium duty flywheel housings from other V-8s. like the 6.5 or even a 366..
-Christopher
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