I have had my 91 Z28 for 3 years or so and have always assumed it has the factory 305 (5000cc). After pulling the engine, I see stamped on the back of the block top drivers side GM 5.7L.

So is this a 350? If so it explains a few things.....

 

Yes, it is a 350.

 

Must not be the original motor. Pretty sure there were no 350 + T5 cars, right?

 

Shouldn't have been, no. Sounds like a swap. RPO codes can confirm

 

Look at the block just in front of the passenger's side head. There's a flat pad stamped with a code and a partial VIN. If the partial VIN matches the cars VIN, it's the original block.

 

Nope number there is completely different than VIN. Someone before me must have swapped motors.
It makes sense, the factory 305 tune was way too lean for this motor. I always figured it was because of the headers, but the displacement must have made a difference.
Anyway, if anyone in Oregon or nearby is looking for a 5.7 TPI, let me know. It runs good, I have a factory ECU EEPROM and a Megasquirt tune that I spent a bunch of time on...