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Old 02-12-2011, 02:36 PM   #1
Vintage Windmills
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1960's GMC V6 engines

Why were the compression ratios so low (7.5:1) on these engines? As far as I know, the only reason could have been to prevent knock. Was fuel that low in octane back when these V6's were designed?? Anyone know what it was back then? I tried googling it and it was just endless pages of definition of octane and how it is determined. I would love to see a table of octane ratings over time. The higher the compression ratio the more efficient the engine is.
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67 GMC C2500 351V6 TH400, AC, PS, PB (can't decide what to do with. Update, decided to keep and will restore )
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^3 dont run and the others don't see winter either
'86 K30 Cummins "Fireside" thread: http://67-72chevytrucks.com/vboard/s...d.php?t=649649
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Old 02-12-2011, 03:17 PM   #2
DPowers
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Re: 1960's GMC V6 engines

may be able to find more info here

http://www.6066gmcguy.org/
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Old 02-12-2011, 03:24 PM   #3
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Re: 1960's GMC V6 engines

My thought is for the torque aspect, and that the big block V6's were in trucks.
i.e. slow mover trucks, and low temperature goal, and the grunt.
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Old 02-12-2011, 06:15 PM   #4
Longhorn Man
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Re: 1960's GMC V6 engines

less stress on the engine. The tighter you squeeze something, the more likely it is to pop. Keep the c/r low, and the engine will run longer between compression related issues.
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Old 02-12-2011, 06:25 PM   #5
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Re: 1960's GMC V6 engines

So what do you guys think about the octane ratings in the 50's and 60's?


Quote:
Originally Posted by Longhorn Man View Post
less stress on the engine. The tighter you squeeze something, the more likely it is to pop. Keep the c/r low, and the engine will run longer between compression related issues.
I thought about that too but look at the longevity and reliability of some of the highest compression engines (diesels) and that doesn't make sense either.
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67 GMC K1500 Custom- 305V6 SM420, PTO, Ram Assist, yellow (the outcast) (project period correct upgrades)
67 GMC C2500 351V6 TH400, AC, PS, PB (can't decide what to do with. Update, decided to keep and will restore )
86 CHV K30 502 th400, apple red NEW
71 CHV K20 350 SM465, ochre (saved work truck)
71 CHV K20 292 SM465, white, tach, PTO, (future project)
72 CHV K20 350 350th, medium blue (project stocker)
01 CHV K2500hd crew, indigo blue

^3 dont run and the others don't see winter either
'86 K30 Cummins "Fireside" thread: http://67-72chevytrucks.com/vboard/s...d.php?t=649649
'71 K20 "get driveable" thread: http://67-72chevytrucks.com/vboard/s...d.php?t=590642
'72 K20 Build Thread: http://67-72chevytrucks.com/vboard/s...=493477&page=6
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Old 02-12-2011, 06:41 PM   #6
Longhorn Man
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Re: 1960's GMC V6 engines

apples to oranges. Diesels (which you hardly saw back then) are build much stronger and heavier. Even the craptastic 6.2 was heavy compaired to a small block.
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