# 455; Pontiac vs Olds



## TheMonkey (Mar 26, 2006)

Hi from a newbie. I've done some creeping around the forum, and it seems like a knowledgeable crew. If I'm in the wrong forum for my question and or anticipated project, please point my in the right direction  

About a year ago, I almost bought a convertible '67 le mans with a 455 in it. It was very sweet, but I pussed out. Still haven't forgiven myself, so I would like to build one on my own.

I am looking for a 67 le mans / tempest to customize. I am at the front end of this project, and don't know much about what I'm getting into, but I'm the type of guy that appreciates a project not only for the end product, but the education.

I have an OLDS 455 motor that was built up for high horse power in a jet boat. Is there any crossover genes between the Olds 455 and Pontiac? The guy that I was going to buy the Le Mans from said his Pontiac 455 bolted right in, but would I be asking for trouble to try to put the OLDS into a Pontiac? What are the differences?

Thanks in advance.


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## G.T.O (Dec 28, 2005)

Both Olds big-block and Pontiac engines were used in the mid-late '70's Trans Ams. It's probably not that big a project to put the Olds engine in a Lemans, but I'm not an expert.


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## DaveH (Jan 20, 2006)

I think some marine engines also rotate the other way, which would necessitate a cam change. I think the only other issue would be motor mounts and positioning. I expect you could relatively easily mate the Olds lower motor mounts to the frame by drilling some new holes and bolting them in place. Just get it straight!


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## lars (Sep 28, 2004)

The Olds 455 will bolt right in any GM A-body car - the LeMans chassis is the same as the Cutlass chassis ("A" body). You will need to obtain all the Olds pulleys and accessory brackets in order to get the alternator and PS to bolt up, and you'll need the Olds Cutlass exhaust manifolds. You'll need to get '67 Cutlass 400 engine mounts for the engine, and this will bolt right up to the mounts in the 67 LeMans chassis. The Olds bellhousing pattern is the same as Pontiac, so the Pontiac tranny will bolt right up. Should be an easy swap. But for as cheap and available as Pontiac 400 engines are, I can't see any reason not to use a Pontiac engine in the Pontiac...


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## TheMonkey (Mar 26, 2006)

Lars- Thanks for the great info. Super helpful.



lars said:


> But for as cheap and available as Pontiac 400 engines are, I can't see any reason not to use a Pontiac engine in the Pontiac...


I suppose that makes sense. But then, part of me can't help but think bigger is better.

Seems to be pretty easy to find a market to buy and sell this stuff, so I suppose I shouldn't get to bent on using what I already have.

The Pontiac 455 is bigger than the 400 (again... my knowledge is crude - I'm at the front end of my project), would there be benefits to getting a Pontiac 400 instead of a 455? (cost, parts, availabilty, durability, etc ?)


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## DaveH (Jan 20, 2006)

The 400 in my '66 pulls harder at high rpms than the 455 in my '70. The 455 has all the low-end torque you could ever want though. I think this is due largely to the fact that the 400 is nearly square (bore=stroke) while the 455 is over-square. Of course this needs to be qualified by the fact that the engines are built-up a bit differently and installed in cars of different weight, transmissions, rears,.....

Many of the internals are interchangeable, so I don't think there's a big difference in the costs and availability bewteen the two motors.


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## TheMonkey (Mar 26, 2006)

DaveH said:


> The 400 in my '66 pulls harder at high rpms than the 455 in my '70. The 455 has all the low-end torque you could ever want though. I think this is due largely to the fact that the 400 is nearly square (bore=stroke) while the 455 is over-square. Of course this needs to be qualified by the fact that the engines are built-up a bit differently and installed in cars of different weight, transmissions, rears,.....
> 
> Many of the internals are interchangeable, so I don't think there's a big difference in the costs and availability bewteen the two motors.


Thanks Dave. Low end torque is something I learned to love with my Duramax truck.

Question though.... how different do you think the two motors would sound? Assume you have the same exhaust, the 455 sounds more meaty? I'm just wondering if it is materially different sound.


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## lars (Sep 28, 2004)

No difference at all assuming cam profile and mufflers are the same. I have both 400s and 455s, and you can't tell them apart from sound.

There is a substantial difference in price bewteen 400s and 455s. Used 400s are currently selling for about half the cost of a 455.


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## kerno (Apr 6, 2006)

There will come a time when you want to sell the car and you'll find a lot bigger market for the car if it has the Pontiac engine rather than the Olds. I think you'll find that by the time you get all the parts required to make the Olds work, you'd have spent less buying and/or building the Pontiac. Also, the F-body (Firebird) exhaust manifolds are identical to the A-body (Le Mans), so an engine out of a Firebird is a drop in.


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## kegbelly (Mar 23, 2006)

kerno said:


> There will come a time when you want to sell the car and you'll find a lot bigger market for the car if it has the Pontiac engine rather than the Olds. I think you'll find that by the time you get all the parts required to make the Olds work, you'd have spent less buying and/or building the Pontiac. Also, the F-body (Firebird) exhaust manifolds are identical to the A-body (Le Mans), so an engine out of a Firebird is a drop in.


:agree 
Stick with Poncho power if you can.


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## usmarines4u2002 (Feb 28, 2008)

*olds 455*

i have a olds 455 in my 71 gto clone ... the torque is outrageous and the H.P. is great stock depending on the year ur engine and model it came out of .... the only mods i made was buying new engine mounts and drilling 1 new hole... and they fit right in ... i have a 71 pontiac 455 i was going to put in it but after i did the research on the 2 engines the olds numbers were way higher . its ur call ...dont get me wrong i love pontiac...but on the strip its all about who is faster and the cheapest way to get there


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## geeteeohguy (Feb 2, 2008)

I'm a Pontiac Guy thru and thru, but I was a journeyman mechanic forover 17 years, and worked on a LOT of engines. The Olds is GM's most bulletproof big-block. They run hard as hell, and hold up well. Very good alloys and quality contol in those old Olds big blocks. That said, if you're looking for a Pontiac, stick a Pontiac engine in it, for the reasons listed above. Or, how about an OLDS? You have yet to get a car, so why not find a clean '64-'72 Cutlass, F-85 or 442, (cheaper than Pontiac's to buy), and stick that big 455 in it? The Olds A body cars of that era had great build quality second to none, and look ALMOST as kick ass as Pontiacs of the same era. The WORST GM Big-Blocks? Cadillac, hands down. Low power, poor breathing, weak rods, and on and on.....Have fun!
Jeff


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## Eric Animal (Oct 28, 2007)

:agree If you have a good OLDS 455 why not do a nice 66-67 OLDS 442/Cutlas resto-mod ??? You would end up with a sweet ride that is not that common.......Or get a GTO and put a Pontiac engine in it. :cheers Eric


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## 5hundo (Sep 10, 2007)

I've got a 67 Le Mans with a 455 Olds.

It's not a hard task to put the engine in. You will run into some tight clearance problems right around the A-arms, but a little work with an angle grinder will get you the space you need. On the left side, the steering shaft will also be pretty close to the header but it still clears (barely  ).



> But for as cheap and available as Pontiac 400 engines are, I can't see any reason not to use a Pontiac engine in the Pontiac...


:agree

When my brother bought this car, it had the 455 with a spun bearing. He B&B'd the engine, and I helped him put it in. He lost interest and sold the car to me. That's the only reason the Olds engine is still in there. It's not that the 455 Olds is a bad motor, it's just that if you have a Pontiac, why not use an engine from the same manufacturer? 

If it weren't for the fact that the Olds motor I have is virtually brand new, I'd pull it out and put it in a Cutlass (or something). If I find a good enough deal on a 455 Pont, that still might be what I'll do but time will tell.


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