All 1965 GTOs came with a V8 389 cubic inch engine, with either a 4 barrel carburetor (335hp) or a 3×2 barrel carburetor Tri-Power (360hp). Automatic or manual transmissions were available.
The PHS (Pontiac Historical Society) documents this vehicle as assembled in the 4th week of December 1964, with a Tri-Power setup, backed by a 4 speed manual transmission.
We are not sure what happened to the original engine. When we purchased the vehicle, it came with a freshly rebuilt 1966 4 barrel. It had also been converted to an automatic and came with a 1967 Muncie 4 speed transmission.
As we restore the vehicle, we are also going to restore it back to the correct engine and transmission.
Identifying a Correct Engine
In 1965, Pontiac did not stamp the VIN on the engine. The engine block and heads were stamped with a part number and date code. For this reason, we have no ability to identify the original engine, even it was still out there somewhere.
The engine block was stamped with a production date code, a block casting number and an engine code. Part of the engine code comprised of two letters that correlate to the engine/transmission configuration for that car. In our case, this is “WS”. A correct cylinder head is stamped with 77.
As the cars were assembled on the line, the engines were taken from stock. Anything with a date stamp within a month prior to car assembly could reasonably have been used in the car. Back in October 2019, we located a Tri-Power WS stamped engine with the date stamp of mid-November 1964.
Identifying a Correct Transmission
In 1965, the transmission was stamped with a partial VIN number and date stamp. The original transmission is gone from the car, so the closest we can get is a date acceptable transmission… it will have a different VIN.
Finally in March 2020, we found a manual 4 speed transmission. VIN numbers were sequential on the assembly line. The VIN number on this transmission is within 900 of our car, so it came from a car made the same week as ours.
We are now ready to rebuild the engine and transmission and start the restoration!
For more information on the history of the Pontiac Tri-Power: