Max compression ratio on pump gas
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Max compression ratio on pump gas
I'm getting ready to start my 460 rebuild. I'm considering aftermarket heads and was curious as to which combustion chamber size/piston configuration I should go with. The truck will not be a daily driver but will be expected to tow so it has to run w/o detonation on premium pump gas. Cam will probably be split profile in the 260-270/490-500 range, dual plane intake, Holley 850 vac. sec., and headers, ZF 5 speed with 4.10s. Would flat top pistons with 72 cc quench heads run on premium? If not, what would be the best combo?
Post Fiend
Joined: Mar 2004
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From: Union, Washington
Maximum pump gas compression depends on a number of things. Static compression is constant (what the numbers tell you), but dynamic compression (what you get withe the engine running) is flexible. Dynamic is effected by static compression, combustion chamber size and shape and cam duration and lift. Static compression, you need to keep under 10 to 1 if you are willing to run premium gas.
Oh and I agree, the 850 is way to big. The stock carb is a 600 and anything bigger than about 700 to 750 is way to much.
Oh and I agree, the 850 is way to big. The stock carb is a 600 and anything bigger than about 700 to 750 is way to much.
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I'm surprised how adamant you both are about the carb size. A while back I was reading an article in Hot Rod describing a 460 build up. The goal was a streetable 500 hp/500 lb. ft. of torque. The engine was not particularly radical and their initial carb choice was a 780 Holley. When their dyno numbers fell short of their expectations, they started looking for vacuum leaks, etc. When everything checked out they decided to go with an 850 Holley. The hp and torque numbers jumped dramatically. Yes, the factory carb for a STOCK 460 was a 600. I wouldn't expect the stock engine to flow as well as one with modern, aftermarket heads with bigger-than-stock ports and valves as well as a free-flowing exhaust system that includes headers.
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
I'm surprised how adamant you both are about the carb size. A while back I was reading an article in Hot Rod describing a 460 build up. The goal was a streetable 500 hp/500 lb. ft. of torque. The engine was not particularly radical and their initial carb choice was a 780 Holley. When their dyno numbers fell short of their expectations, they started looking for vacuum leaks, etc. When everything checked out they decided to go with an 850 Holley. The hp and torque numbers jumped dramatically. Yes, the factory carb for a STOCK 460 was a 600. I wouldn't expect the stock engine to flow as well as one with modern, aftermarket heads with bigger-than-stock ports and valves as well as a free-flowing exhaust system that includes headers.
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