I may be purchasing a 1966 GTO Convertible. The owner claims its a 389 tri-power engine. Im new to the GTO's and Im really trying to make sense of the engine codes. This particular car has a "YC" engine code. According to my research, the "YC" Code represents a 455 *** What makes it a bit confusing is that the codes on the distributor pad show the engine was produced on Nov 6th, 1966. So, if the 455 wasen't indroduced until 1971, but the engine was created in '66.....is this a 389 OR 455?
Can someone help? Thanks in advance.  

Pontiac tended to reuse engine codes and judging from the production date, you have a 1967 265hp 400that was originally in front of an automatic. Even if you read the production date wrong and it is a 1966 389 YC motor, it is a 290hp/auto not a 360hp tripower. Double check the block casting # and date code to be sure. A great website for this info is  http://www.wallaceracing.com/  scroll down the left hand side of the page and click on "pontiac engine codes", not "engine code search". This will show you all the codes for the various years. Their website has tons of this kind of info. Check it out.
Steve

PS:the guy may not know that he hasn't got the right engine, lots of people buy musclecars from dealers and just take the salesman's word for it. Show him the website too, he may need it to find out what he really has!  

Thanks for the info! Ill be sure to pass the message along. How can I verify these numbers? I noticed alot of pontiac guys use the PHS stuff. Also, to make things a bit more complicated.....the car has a 4 speed. Im just trying to take all these things into account before I make reasonable an offer. So are you saying he could have a 1967 convertible GTO with a 400 engine and a tri-carb set-up? And with that, he changed the tranny to a 4 speed?
Thanks again!  

All I'm saying is that the engine he has, assuming you read the production date code correctly, is a 67 265hp 400 originally in an automatic application. The car could originally be a 1966 GTO convertible, 389/360hp tripower/4 speed car. It just doesn't have the correct size/year block. If you really intend to buy the car, send the vin to PHS and find out for sure what the car was built with. If it is what he says it is and the car is otherwise correct, all you need is to find a correct block, as long as the price reflects the fact that the car is not #'s matching.
Steve