I have my PHS report back and was lead to believe the car in question was a 455 but the report is saying 400.....could the report be wrong and generalising?? Or is there another was to decipher the build sheets they send!!!!

 

Proud to say it was built here in Pontiac Michigan!!  If that car could talk.

I doubt it is wrong for your VIN number. Your car was born with a 400 engine.

Now you believe it has a 455? One way to check if you have the original engine in your car. Look at the front of your engine. To the left of the water pump (passenger side), just below the cylinder head should be some machined letters and numbers. What are they?

Since your PHS documentation said your car is a 400, the letters YS should appear on that area. It should also have the last six digits of your car’s VIN number. This means this block/engine was born with your car. If YS is not there or the numbers don’t match, then your engine has been replaced, possibly with a 455. A 455 would have YA stamped in it. Also Pontiac cast the block’s factory displacement on the outside of the block. You should see a 400 or 455 cast into the engine block above the oil pan.

Another thing to consider. Pontiac V8s never had a big block or small block program. They had displacements range from 303-455 but the exterior block dimensions were the same, Pontiac varied the bore and stroke to get different displacements. So you could have a 400 block that has been bored and stroked out to a 455.

Edited May 17, 20242 yr by Frosty