Topic: Replacement engine - 403ci Oldsmobile

[Galeotti]

Hi to everybody. I have a 78 Firebird Formula 403ci (Oldsmobile engine) and TH350 automatic trasmission and I would like to replace the engine with a more powerful one (400-500hp and great torque). Could someone suggest what engine could fit my car without big support changes? Do you think I need to change the trasmission?

Thank you.

[EJ]

I have a 79 with a 455 olds big block. Huge torque and horsepower potential. The 455 olds will mount directly to your 403 mounts. The trans I have is the 350 TH. You will have to modify the headers a little. Research the 455 olds early year castings. Also the heads iIhave are the C castings which are the desired iron heads. A cam 10.5 to 1 and a little head work and your in the mid 400s HP and 500s in torque.