1964 Pontiac Tempest Lemans Convertible

Engine Mini-Series – Pontiac's 326 Prt 2 - AACA Forums

There is no big or small block Pontiac V-8 engine, ALL Pontiac engines from the 1955 287 to the 455 have the same external dimensions and the bore centers are the same, in fact all engines can use the same connecting rod as the rod length ( 6.625 ) is the same as well as the crank throw journal the same diameter. All Pontiac engines are known as a medium block. Helfen, I agree with everything you say. People seem to need to define all V8 engines as big or small blocks and most aren't aware that all Pontiacs (at least from 1955 into the late 1970s) used the same lump. As you say they are 'medium' blocks; weight is between the small and big engines of their rivals. Interchangeability is a can of worms but is at least well-documented. I ran a 455 with #62 heads on my 1965 Bonneville. It ran 14.1/102 with its original TH400 and 2.56 rear. I did a 12,000 mile tour of the US in 1978 in a '67 LeMans with a 326. It got about 22mpg over the whole trip at a cost of 3c/mile - those were the days. Helfen, I agree with everything you say. People seem to need to define all V8 engines as big or small blocks and most aren't aware that all Pontiacs (at least from 1955 into the late 1970s) used the same lump. As you say they are 'medium' blocks; weight is between the small and big engines of their rivals. Interchangeability is a can of worms but is at least well-documented. I ran a 455 with #62 heads on my 1965 Bonneville. It ran 14.1/102 with its original TH400 and 2.56 rear. I did a 12,000 mile tour of the US in 1978 in a '67 LeMans with a 326. It got about 22mpg over the whole trip at a cost of 3c/mile - those were the days. That is very impressive numbers on that Bonneville and I bet you ran the quarter as a two speed. I have three sets of gears in the LeMans and one of them is a 2.56. My LeMans weighs 4050lbs and with those gears I would do 105mph in second at 5,200rpm and get 24mpg, but with todays 10% ethanol I only get 20mpg. I remember seeing a article in HPP about a 66 Bonneville convertible with a 376hp tri-power 421 going 13.90 @ 100+. That is very impressive numbers on that Bonneville and I bet you ran the quarter as a two speed. I have three sets of gears in the LeMans and one of them is a 2.56. My LeMans weighs 4050lbs and with those gears I would do 105mph in second at 5,200rpm and get 24mpg, but with todays 10% ethanol I only get 20mpg. I remember seeing a article in HPP about a 66 Bonneville convertible with a 376hp tri-power 421 going 13.90 @ 100+.

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