will a 455 olds engine fit in a 1981 trans am?

Question

how much modifing will i have to do? I have a 455 olds engine and 400 trans.

Answer 1

1981 TAs had either a 4.9 Pontiac or 5.0 Chevy as the only available engines. The Olds motor will bolt up to the tranny (but there is no way I would use that tranny behind the 455). I think there will be lots of mods to make this work.

A much better solution would be to use a Pontiac engine. It will slip in and bolt right up with almost no modifications. I still wouldn't use the stock trans, but Pontiac had used a TH400 in that body before. So all you will need is a mount or possibly a different crossmember.

Remember to install subframe connectors, or your car will twist apart under all the new torque.

Update: Yes, the '79 bird had the 403! If you use those mounts, your olds mill will bolt right up. But then you'll have wiring and cooland hose issues to deal with - not too major. I'm assuming you will use headers and custom pipes, there should be enough people around who can do that work for you if you can't.

Answer 2

These cars came with an Olds 403 in the late '70s. The 455 is the same externally except the deck height. All of the parts could be used from one, or bought at an auto parts store. If the engine is a Chevy, the transmission that's in the car won't work. If it's a Pontiac engine, the transmission will work. I don't know what transmission is in the car, but I wouldn't use any automatic other than the TH350 or TH400 behind the 455. The TH400 tranmission you have will work in the car and bolt right up. Depending on whether it's a long shaft or short shaft, you may have to have the driveshaft shortened or a custom length made. The only other issue is headers. Due to the deck height difference, headers for the 403 won't work, but factory exhaust manifolds probably will. If the 455 has manifolds, try them. If they don't work, try a set off a 403 car or a set of headers from an A or G body with this engine.

Answer 3

You can buy heavier front springs to handle the additional weight of the 455. I know the pontiac 350, 400 and 455 weighed almost exactly the same. I believe the 455 olds is nearly the same weight as the pontiac engines. The driveshaft will have to be modified to fit. A simple and fairly cheap modification. Motor mounts will likely needs changed, not a big deal. You may have to modify or change the trans cross-member to mount the 400 trans.

I have a friend with a 400 chevy in his 1981 TA. You can almost walk around the engine in there.

The B-O-P (Buick - Olds-Pontiac) transmissions are different from the chevy transmissions although there are some years (I believe yours is one of them, post 1979 when the "corporate" engine idea started) that were a universal bolt pattern. The BOP's have a dip in the top of the trans housing where the "older" chevy trannys were round tops with no dip. If you use the turbo 400 tranny with the 455 it is a good choice for strength. Some guys use the turbo 350 but you really have to build one good to hold up. One of the overdrive trannys will work as well I am not sure which one is best, 200R4 or the 700 R4. If I recall the 200R4 is really better as it is not electronic. And YES it will hold up... the problems inherent with the original design have been addressed by some of the better transmission rebuilders and they hold up well under the power load.

PS: if somebody mentions "big block" when referring to a BOP motor you can just smile. The 350-400-455's were all the same size! Big block is a chevy term! ;-)

I currently own a 1978 trans am and we are trying to decide on using the 455 olds or the 455 pontiac setting on the bench for the new build-up! Already have higher rate springs...

Answer 4

Way to much work, your suspension in not even strong enough for all the weight from such a heavy motor and, your shaft in not the correct length.

A 400 Poncho with a 350 turbo transmission would be a better choice, even much lighter, still a hole lot of work.
I understand you have a motor & tranny laying around but there are too many half-breed 2nd generation T/As out there.

Answer 5

Very likely it will fit in your Trans Am but you have to do alot of modifing.

Answer 6

I had a 1979 pontiac firebird trans-am----with the 6.6liter 403 oldsmobile engine-----original engine---pretty sure it had a turbo 400 also------I don't see why you can't make it work----

Answer 7

Depending on the motor wether chevy motor or pontiac motor. if had pontiac motor just a little motor mount adjustments

Answer 8

If it had an Olds 403, none.

Answer 9

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