Engine replacement options

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JodyPackerfan

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Feb 2, 2020
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Racine, Wisconsin
I've been reading through a zillion posts on this subject but havn't really got the answer I'm looking for. Other than the intake manifold; does any GM 455 work as a direct bolt on to our coaches? Such as 455 from Buick's, chevy ect,,,? any year limitations?
 

JSanford

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Oct 4, 2019
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Sacramento, CA
Oldsmobile and Buick were the only ones that made a 455, and they are completely different engines.

You can "easily" swap in any of the engines used in the Toronado: Oldsmobile 350, 403, 425 and 455. You can also use any of the Eldorado engines: Cadillac 368, 425, 429, 472, and 500.
 

Mike Perez

Administrator
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Oct 2, 2019
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Oldsmobile and Buick were the only ones that made a 455, and they are completely different engines.

You can "easily" swap in any of the engines used in the Toronado: Oldsmobile 350, 403, 425 and 455. You can also use any of the Eldorado engines: Cadillac 368, 425, 429, 472, and 500.
That's not exactly correct. Chevy had it's own Bolt Pattern for their engines. The other common bolt pattern is known as the BOP pattern. "Buick, Olds, Pontiac". Also, Cadillac used the BOP pattern. Pontiac did have a 455 although it was really a 456.

https://en.wikipedia.org/wiki/Pontiac_V8_engine#SD455

The limitation on the BOP pattern engines is the intake manifold height. The Toro manifold is in the valley and thus doesn't interfere with the hatch. All other big blocks will hit the hatch without raising it as I understand it.
 
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JBurt

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Oct 8, 2019
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It depends on what you mean by "direct bolt in" and your fabrication skills. A 455 or 403 out of another motorhome would be the only direct bolt in. Any thing else you will have to deal with things from brackets, linkages, and pans. Even a 455/403 out of a Toronado will require brackets, intake, and carb. (There is a difference in the internals of the carbs, even from year to year)
 
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Matt Colie

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Oct 25, 2019
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If you are looking for engines, be aware that only Oldsmobile and Cadillac share the same rear face of block and not even all of them. So, unless you are ready to deal with that, derail that train of thought right here.
Matt
 
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tmsnyder

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Oct 7, 2019
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Buffalo NY
It's always going to be easiest to replace one engine with another exact same engine, and definitely if it's actually the same engine; you know it will fit.

As far as swaps, without getting into a whole discussion about why it's a bad idea or a good idea, just thinking about the possibility of the swap; what is needed to swap a 1st generation small block chevy into a GMC motorhome? I believe this has been done with BBC engines with an adapter plate, and since the rear block face is the same between the SBC and the BBC it would be the same adapter plate I believe.

Anyone know the details of mating a SBC and a TH425 ?
 
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tmsnyder

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Buffalo NY
I believe for a direct bolt-in with absolutely no fabrication or modification you are limited to the Olds 455 and reusing your old intake, brackets, etc. Every other replacement engine is going to require some level of fabrication / modification.

I've been reading through a zillion posts on this subject but havn't really got the answer I'm looking for. Other than the intake manifold; does any GM 455 work as a direct bolt on to our coaches? Such as 455 from Buick's, chevy ect,,,? any year limitations?
 
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Matt Colie

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Oct 25, 2019
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Todd,
From what Dave Lenzi has shared, only the dowel pin holes reliably share locations on all GM products. Apparently, you can use those dowel pins and two bolts can be made to work (the lower two iirc) and that leaves having to do an Lenzi type thing to get to four.
Matt
 

JodyPackerfan

Active member
Feb 2, 2020
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Racine, Wisconsin
I believe for a direct bolt-in with absolutely no fabrication or modification you are limited to the Olds 455 and reusing your old intake, brackets, etc. Every other replacement engine is going to require some level of fabrication / modification.
Yah, I have no intention of putting anything buy a 455 from motorhome - Just curious what the options are ect,,,
 

Matt Colie

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Oct 25, 2019
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Jody,
Actually the answers without serious fabrication are:
Oldsmobile 455
Oldsmobile 403
Cadillac 472
Cadillac 500
The Cadillacs will all need some creative front mounts.
Matt
 
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tmsnyder

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Oct 7, 2019
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Buffalo NY
True but he asked this "Other than the intake manifold; does any GM 455 work as a direct bolt on to our coaches? "

Do any of them work with absolutely _zero_ fabrication ?

Lots of engines can work but all require some amount of fabrication, he was asking for a direct bolt in swap.

Jody,
Actually the answers without serious fabrication are:
Oldsmobile 455
Oldsmobile 403
Cadillac 472
Cadillac 500
The Cadillacs will all need some creative front mounts.
Matt
 

Matt Colie

Active member
Oct 25, 2019
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True but he asked this "Other than the intake manifold; does any GM 455 work as a direct bolt on to our coaches? "

Do any of them work with absolutely _zero_ fabrication ?

Lots of engines can work but all require some amount of fabrication, he was asking for a direct bolt in swap.
Todd

I truth I do not know.

Both Buick and Pontiac made 455s as I recall. I know the Pontica would be a GM RFB, and I believe that buick is as well.
You would even have to ask those that did the Cadillac about the front mount. So I guess that is pretty much a NO.

What you have to see at some point is a Dave Lenzi 8.1. That is a thing of beauty.

Matt
 

turbobill

New member
May 25, 2020
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The only "direct bolt in" for a 455 in a coach is another 455, 425, or 400 Oldsmobile big block (tall deck). All the Oldsmobile small blocks 1964 to 1990 (shorter deck height) are bolt ins for the 403 (which is also the shorter deck small block). The small blocks are the 260, 307, 330, 350, 403 and the 260 V8 and 350 diesel.

Small blocks and big block Oldsmobiles directly interchange (bell housing and engine mounts) but you must use the flex plate from whichever engine you are using and the tall deck blocks will have the accessory brackets higher (some may be slightly different) and the belts are longer. Use the motor home oil pan. (pans interchange small to big block as do many other parts)