As C1 says they were never sold. I have an original 73 LeMans GM Canada sales brochure and the 455 SD is listed as an option with 310 Net HP, well over 400 Gross HP for all 2dr LeMans, LeMans Sport and Grand Am. Since GTO was a LeMans option it would have been avaialble on GTO too.

My GM Canada owners manual makes references to it as well, fuse box diagram shows fuse for solenoid operated ram air system that would have gone with it.

The folk lore suggests that GM could not get the engine EPA certified because they played a trick with the EGR and got found out and nosie from the Ram Air was too intrusive.

455 SD engines did find there way into Firebirds in 1974, rated at 290 net HP.

If you ever come across a 1973 LeMans, GTO or Grand Am and the 5th digit of the VIN is "X" you will have found the Holly Grail!

The President of the GTO club of Ontario built a one of none 455 SD 1973 GTO and showed it at Perfomance World 2008 a few months back.

-- Edited by 73SC at 00:19, 2008-06-17

They named GTO Best Perfomance Car of 1973, they tested it in base 400/230 net HP, optional 455/net 250 HP and 455SD/net 310 HP. Of course they liked the SD best but the handling and other parts of the package were evaluated too. So in order for them to test one there had to be at least one GTO 455 SD built, but at the end of the day it was GTO that was best perfomance Car for 73 not the GTO with the 455 SD.

So I guess there is a bogus blue 73 GTO with a 455 SD.That,s a shame,because the SD put out the same torque as the 428 Hemi.
Pontiac only put out about 400 455 SDs in 73 on thier Firebird line and 950 in 74.
I wonder what happened to the couple of factory cars that were made?Crusher or put the 400 back in