The '73 LeMans came with the 350 Pontiac 2-barrel engine as standard equipment. The GTO came with the 400-4-barrel as standard and the 455 as the optional engine. The LeMans and GTO look very much alike, but if the car had LeMans grilles with a 350 emblem, chances are good that it was not a GTO...
That Pontiac 350 was basically a Pontiac 326 bored out a bit (the standard 400 cube V8 available in the GTO was a 326 bored out even more than the 350). It had a 3.875" bore and 3.750" stroke. It was actually 354 cubic inches but Pontiac called it a 350 for some reason. It was in the 1974 Ventura based GTO but not the 1973 LeMans based GTO.
The interesting thing about all that is that Pontiac kept the same stroke for the 326, 350 (354), 389 and the 400 (3.75" stroke).
When Chevy went from 350 to 400 cubic inches on their small block, they changed both bore and stroke. The 350 Chevy has a short 3.48" stroke, so the 350 Pontiac actually made more torque.
When the Chevy guys want to get torque (and horsepower) out of their 350s, they install a Chevy 400 crank to get 383 cubic inches. The Chevy 400 crank has a 3.75" stroke.... just like the Pontiac. The Chevy guys, in building thier 383s, are building an engine with almost the exact same bore & stroke as an old Pontiac 389. (389 is 4.063 x 3.75, and the 383 Chevy is 4.030 x 3.75) The small block Chevy 400 has the exact same bore & stroke as the 400 Pontiac (4.12 x 3.75), and that's the hot ticket for a small block...
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