This is one of the more interesting facts of owning a 1973 GTO. GTOs in
1973 were offered in two different engine flavors:
- a stock 400 cid/4bbl @230 net HP
- a stock 455 cid/4bbl @250 net HP
Hi-Performance Cars Magazine did a test of a 1973 GTO and named it "Supercar of the Year!" Here's why: the test car was not the ordinary stock 455. It was a super duty 455 with 310 net hp. This was supposed to be an option for the GTO but was pulled by the Pontiac right at the last minute and only offered in limited numbers on the Formula and the Trans Am. Accounts vary on why this was done, but one source indicted that the builder of the connecting rods could not supply enough rods if the Super Duty was offered on the GTO.
To the left: Here is the 1973 April issue of Hi-Performance Cars magazine which lauded the "Phantom" super-duty 73 GTO.
| 73
facts about 1973
Model show rods released by Monogram models this year: Troublemaker, Fire Iron, Quicksilver, Cop Out, California Street Vette, Fast Buck, Li'l Van, Outcast (57 chev). |
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73
GTO Odyssey Music
Some Kind of Wonderful....Grand Funk Railroad |
73
facts about the GTO
Emissions stuff is good for breathing clean air, but (generally)
bad for engine horsepower. In 1973, there were three engine emissions
controls:
crankcase emission control through the air cleaner housing, evaporative
emission control, and the new Exhaust Gas Recirculation,
or "EGR" system.
Lamenting the loss of power from the new EGR system in the 1973 GTO, a clever Pontiac engineer found a loophole in the EPA emissions rulings. What this engineer noticed was that the EPA test for emissions lasted only 50 seconds because the "bags" containing the emissions were limited in size. Hmmmmmmmmmmmmmmmmmm. Pontiac engineering developed a timer that shut off the EGR solenoid valve after 53 seconds--thereby improving engine operation. They passed the EPA tests and got a performance boost to boot! (he he he he he ha ha)
The EPA was not amused. Once they found out, they ordered Pontiac to change the 1973 GTO engine's EGR shutdown timing system by March 15, 1973. So 1973 GTOs have one of two engines:
1. The lighter blue engine constructed before March 15
2. And the darker blue engine constructed after March 15
My 1973 GTO seems to have the lighter blue engine, but I'll have to check some numbers to see if it was actually constructed before March 15, 1973.