I'm working on a Firebird for my daily driver and I was wondering what engines would fit a tranny? It currently has a Oldsmobile 403 (father in law says its a big block) that needs a rebuild. It has a new tranny with a shift kit so I don't like the idea of switching the tranny out. I however, would like to get more than 6 mpg and would be rebuilding the 403 later once I can afford another car.
Your father-in-law is wrong - it's a small block (basically an Olds 350 with big pistons), but it doesn't really matter. The transmission has the Buick-Olds-Pontiac-Cadillac bellhousing pattern. There are a wide variety of engines that will fit that. It was standardized around 1960. Any B-O-P-C engine used in a rear drive car after 1960 will fit the tranmission, except for the Buick V-6's built after about 1988 or so and used in Firebirds (which are rear drive, of course). I don't think any other rear-drive BOPC engines were actually built anyway after the mid - 80's. I guess the Olds 307 was the last of the BOPC V-8's.
As you can probably guess, any small-block Olds V8 will bolt right in, and any Pontiac V-8 is fairly easy to put in because there are so many Pontiac-powered Firebirds to rob parts from.
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.