Compression?
12-20-2001, 10:43 AM
#1
Racer
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Compression?
What kind of compression ratio can I get away with on my 71? I have the 487 76cc heads and am running a stock ratio of 8.5 now. I would like to get at least 9.5, but 10 would be better. I will be installing a Crane Blue Racer 284H cam. Specs at .050 lift are 218 intake and ex. .450" lift with 1.5 rockers. 284 add. duration. I am planning on using the stock heads, manifold, carb, and rams horn exhaust manifolds. Any help will be appreciated.
12-20-2001, 10:52 AM
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Drifting
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Re: Compression? (compuvette)
Your better off just getting 64 cc or so heads and end up around 10ish. IMO a wonderful cam is the Crane 272 Power max 216/228 or something like that. the extra exhaust duration helps it breath in a Ram horn restricted environment.
I'm running about 10.5 with a bigger cam.
[Modified by Lt1er, 8:53 AM 12/20/2001]
I'm running about 10.5 with a bigger cam.
[Modified by Lt1er, 8:53 AM 12/20/2001]
12-20-2001, 11:02 AM
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Racer
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Re: Compression? (Lt1er)
The heads on my engine from the factory are 71 LT1 heads with hardened valve seats, so I hate to replace them. I will probably just run TRW domed pistons and get 10:1 and be happy. I just want to make shure that I will not have problems with detonation at 10:1 on 92-94 premium. Thanks for the info, though.
12-20-2001, 09:11 PM
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Drifting
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Re: Compression? (Alwyn678)
9.5:1 is safe. I understand that with a modern head design you can get away with 10:1. Some engines have it higher but I forgot how, something to do with the squish engineering.
But over this you will have problems. I have 11.25:1 on my '70 Caddy and it runs- with retarded timing. This doesn't make it ok since I'm giving up performance to run it on crap gas(93-94). Retarding the timing from optimum is a losing compromise for high compression.
The hardened seats are nothing to worry about not having. If/when your valves recede its time to do the heads again anyway so you have hardened seats installed.
The more radical a cam is the more compression you can take. This is in a narrow spectrum though. Very radical cams leak quite a bit of compression so They can get by with more.
I would say that if you go higher than 9.5:1 plan ahead on thicker gaskets or a head change to enable it to be reduced. If its needed you could do that or retard the timing.
But over this you will have problems. I have 11.25:1 on my '70 Caddy and it runs- with retarded timing. This doesn't make it ok since I'm giving up performance to run it on crap gas(93-94). Retarding the timing from optimum is a losing compromise for high compression.
The hardened seats are nothing to worry about not having. If/when your valves recede its time to do the heads again anyway so you have hardened seats installed.
The more radical a cam is the more compression you can take. This is in a narrow spectrum though. Very radical cams leak quite a bit of compression so They can get by with more.
I would say that if you go higher than 9.5:1 plan ahead on thicker gaskets or a head change to enable it to be reduced. If its needed you could do that or retard the timing.
12-20-2001, 09:27 PM
#7
Le Mans Master
Re: Compression? (mountainmotor)
im running a 350 domed trw pistons..41thousandths gasket, world products sportsman2 heads 72cc heads crane energizer cam 274dur.450 lift 106 lsa 218 dur...no pinging at all on plus.
