Author Topic: Replacement engine - 403ci Oldsmobile  (Read 709 times)

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Offline Galeotti

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Replacement engine - 403ci Oldsmobile
« on: November 13, 2017, 03:48:41 AM »
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.

Offline EJ

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Re: Replacement engine - 403ci Oldsmobile
« Reply #1 on: November 13, 2017, 09:50:46 PM »
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.