Hello everyone!
I joined this forum to get more knowledge on olds motors. Quick run down on my project. My first car was a 79 Trans am. Nocturne blue with olds 403 and auto trans. Well after 20 yrs of not owning the car and wishing to have it back. It showed up at my front door last year for my birthday! I have my dad and oldest son to forever be grateful too for finding the car and buying it for me. The last 20 yrs has not been kind to the car. I am slowly working on it and now have some funds to put into the engine and trans. My biggest issue is figuring out if I want to have the 403 rebuilt or put in a different motor? I know about the 403's bottom end weakness and the 4A heads.
Open to any engine rebuild recipes for the 403 or any suggestions on a different motor for it. Not going chevy, wanting to go with olds or pontiac.

 

welcome to CO I love the TAs

imnot much help on the engine build but here s a recent 403 thread, may be more build than you want but its what can happen !!!

https://classicoldsmobile.com/forums...-478-a-141721/

 

What are your goals with the car?

If the 403 is mechanically sound, install earlier heads, a updated camshaft, some exhaust work and have fun. From what I understand the windowed main webs aren’t as big a deal as everyone makes them out to be. Keep the engine speed reasonable (it’s a torque monster Olds, not a high winding chebby!) and I would think you will be fine.


If your rebuilding the engine, then buy the best/lightest pistons available. The lighter the pistons, the easier life the windowed main webs will have.

Of course, if you can find one of the mythical solid main web 403, your in great shape! 😎🥁

 

As said it depends on the shape of the motor on what you do. If going for a full rebuild, I believe Cutlassefi brought a light weight piston from Autotec in a small dish 4.375" bore to the market. KB also makes a Hyperutectic piston with a 6cc dish. I believe Cutlassefi also offers a 5 main Halo girdle as well now, another good idea. Those pistons work well with factory BBO heads or Procomp and Edelbrock aluminum heads. The early 350 heads with 68 to 70cc chambers flow way better than the 4A on the exhaust side. My 4A heads were 86cc, 84 is the spec. So with 21cc factory pistons sitting. 020" in the hole, factory you are less than 8 to 1. The 350 heads with a clean up milling, around 9 to 1. Another good move is W31 2"/1.625" valves with the bowls opened and an upgraded cam. Also seriously consider a 2000+ stall even if leaving the highway gears in the car. The factory TH350 stalls around 1600 rpm which sucks for launch. Good luck.

 

Thanks for the reply.
I know when funds allow I want to rebuild trans and change rear end gears. My first step is get engine taken care of. Then trans and rear end. Then move onto to brakes, suspension and finally the body work.