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Hi all. I'm going to look at a GMC cabover. It's an ex-firetruck and the guy says it has a 637 gas v-8 engine in it. I don't know what year it is. Early to mid 70's I believe. Is this engine the same family as 454's of that era? Thanks for any help. Ron.

according to the very limited information on the wiki page below, its an oddball. appears to be related to the large GMC sixes not the Chevy big blocks..

https://en.wikipedia.org/wiki/GMC_V8_engine

Hy cff, the 637 V8 was developed from the V6s that came out in 1960, I believe it may be a 60 degree block. The 637 V8 has nothing in common with either the small or big block Chevrolet engines or any V8 engine developed by any of the other GM marques. The V6 engines ranged from 305 cu.in. to 478 cu. in., then the only V8 of that design the 637 and the largest engine of that design the "twin six" 702 cu.in. essentially two 351 engines with a common crankcase, hope that helps.

I used to drive a 637 V-8 in a '71 9500. They are like the big 478 V-6 with 2 extra cylinders "welded" on. Same Cubic Inch per Cylinder. But, they are very different engines. They may look similar but where the 478 is a "lugger" with a lot of torque, the 637 is more of a "revver" like a Detroit. The 637 replaced the 702 in '66. I would have to check to be sure, but believe they were available till at least '72. Not my favorite engine ever made, but I still like them. Keep us posted if you buy it. Bill

The 637 was the largest cu. in. Gas V8 GM ever had in production with 275 HP, 560 lb.,ft. torque and weighing in at 1200+ pounds! These were low rpm engines making max hp at about 2500 rpm. If you didn't know better you would think they were diesel engines...let the clutch out and you had max hp and torque! I had the 478 V6 in a 1970 Chevy Tilt Cab and it was a torque monster! Mike B :)