From 2nd series 1955 through 1959 GMC trucks with V8 engines used Pontiac V8s in the smaller trucks and Oldsmobile V8s in the larger trucks. These engines were based on same year Pontiac and Olds engine, but had (typically lower) compression ratios, different carburation and sometimes different cylinder bore sizes. All engines came from the factory painted red with GMC stickers on the valve covers. All were advertized within 1 cubic inch of the Pontiac & Olds brethern except for the 58/9 Pontiac-based engines which had smaller diameter cylinder bores.
Attachment shows the advertized engine sizes. The 500 and below models used the Pontiac-based engines while the 550 (like this fire truck) and larger models used Olds-based engines.
The '58 and '59 Pontiac based engines were both advertized as 336 cubic inches. But the '58 Pontiac crankshaft had a 3.5625" stroke with 2.623" main journals while the '59 Pontiac crankshaft had a 3.75" stroke with 3" main journals. Both the GMC engines came with smaller (but different) bores. The '58 engine was actually 336.1 cubic inches and the '59 is 336.66 cubic inches.
Last edited by Bill Hanlon; 09/07/20262:31 PM.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
