i own a 88 gta TPI auto, when the guy sold it to me told me it was a 350 but didnt really believe him, the vin tells me its a 305 (F) but im trying to find the casting #, the only # that is all over the block is 878 but cant find anything online about that, if anyone can help, it would be much appreciated

 

You will have a 5.0(vin F) or 5.7(vin 8) on back of the motor on the dr side and it wil be very hard to see.

 

If the VIN has an "F", then the car was originally equipped with the 305 TPI LB9 from the factory. If the engine was replaced and you're just trying to determine the engine size, "878" seems to indicate it's a '96+ 305 vortec roller cam block. Replacement engine block perhaps?

The engine should have a derivative of the VIN stamped on the front passenger side pad of the block unless it was machined off during a rebuild. If the VIN derivative matches the chassis VIN in lower left-hand side cutout of the windshield, then it's the original LB9 305 TPI engine.

 

The only 878 block I can find evidence of is a 96-up 305 truck block. So if that's REALLY the casting #, it's a 305.