Olds 403 to 455 Swap

[MO 1979 TA]

Hi - Have a 79 Trans Am that originally came with an Olds 403 and am planning on swapping in the Olds 455. I am using the Waybackmachine (https://web.archive.org/web/20130719232526/http://transamcountry.com/community/index.php?board=67.40) to dig through this website before it got wiped clean to find relevant information. It's taking a while and none of the pictures were archived...

Anyone still around that has performed a 455 swap and can provide insight? My car has the original A/C box and from what I understand, this is the main issue in the engine compartment along with some of the bracketry (brackets for a/c compressor, alternator, power steering, etc)? I am not going to use the regular shaker but a hood scoop instead if that helps as well as cast iron exhaust manifolds.

Thanks in advance.

[scarebird]

Do you still have the 403?

[MO 1979 TA]

Some things from the wayback machine so far captured as the 455 block moves the head out 1" further on each side in the engine compartment and a taller deck height:

- Use 403 motor mounts
- Use the 455 alternator bracket instead of 403
- Use the 403 Power Steering bracket instead of 455
- If thinking about using headers, ones for a '73 - '77 Cutlass with the 455 are most compatible to the TA frame
- Do not use tall valve covers
- Oldsmobile has 3 different water pump lengths; use the water pump for a 403 onto the 455 or at least one the same length as a 403
- May need to install stiffer coil springs in front due to weight difference of 403 vs 455

[MO 1979 TA]

Do you still have the 403?

Yes and all the hardware (brackets, oil pan, etc.)

[scarebird]

I personally found the 403 to be the better all around motor; lighter, more compact, nicely oversquare.

And you already have it and the brackets.  These may make it nicer:

https://www.summitracing.com/parts/sdm-pce281-2152/make/oldsmobile

On the PY forums they seem to be ok for Pontiacs. 

[Maxthe222]

I personally found the 403 to be the better all around motor; lighter, more compact, nicely oversquare.

And you already have it and the brackets.  These may make it nicer:

https://www.summitracing.com/parts/sdm-pce281-2152/make/oldsmobile

On the PY forums they seem to be ok for Pontiacs. 

x2

Just keep the 403, you're not going to gain much using the 455 with what you can do with a 403 in this day and age.

[MO 1979 TA]

Thanks for the input on the 403 but I am going to stick with the 455. Reason being, the 403 is in pieces and may need a crank, bored .40 over already and is original to the car. One day when the car is restored back to original I'll put the 403 in. Additionally, the 455 came in a trade for free, is complete and has essentially no miles on it although it will need a slight rebuild. I'd just hate for anything to happen to the 403 before the car is put back to original.

[Wallington]

No one ever has, once that engine gets put aside it stays there.

[MO 1979 TA]

No one ever has, once that engine gets put aside it stays there.

Not sure i follow your comment?

[olds403]

Where is the 403 ?  I will get more HP out of it than a 455.
Will be on the dyno at end of Feb.  Mark my words 540HP or more.
The heads flowed just under 300cfm and running a lumpy ass cam with 240 duration at .050
My 350 olds did 505HP on gas and 510 on e85.
The only thing stock is the block.  Rest is modern LS.
Custom LS crank, LS Rods, LS pistons.  LS coils and LS ignition.
Olds......

 I AM OLDS403.

[olds403]

Here is the dyno run.

Nuff said

https://youtu.be/mtH_sDAF_s4