Thread: 500hp 454

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11:1 is possible to run pump gas with.

It is? I don't know anymore, some people say yeah, others say no.

It is all in the cam you can run a cam with a lot of duration that is ground on the correct lobe center and it will bleed off compression!

But then wouldn't it be pointless in a way to have that much compression? Say you wan't 11:1 and then you get a cam that will let some of that compression out, then that is pointless I am thinking. I am not saying I am right here, I am just basically asking I guess you can call it.

One of the primary reasons for bumping up compression ratios is for that very reason, big cams bleed off cylinder pressure. High compression ratios are more for compensation than they are for power in high rpm engines. The other reason is for better efficiency. Torque is directly related to cylinder pressure and hp is a relation between torque and rpm. If we take a torque cam, they actually develop a higher mean effective pressure than a cam that makes a lot of hp, but they torque cam cannot flow enough air into the cylinders at high rpms to make enough pressure to make any power in those rpms. That's where the big cams with tight seperation angles come in. They can flow more than the torque cams at high rpms, but their mean effective pressures are still lower therefore torque is lower. They do make more hp, though, because the engine is spinning faster.

FMXhellraiser, you've got it right....no way are you going to run true 11/1 CR on pump gas. And you right about what you're thinking, if you bleed off compression with a big duration cam, or retart timing to avoid pinging, then you've lost all that you're trying to build. Shorter duration cams, as well as a closer LSA, close the intake valve earlier, keeping more cylinder pressure in the engine....more power! But at the same time, more chance of detonation. It's a trade off, you cant have both...either you want a race engine, and it wont be very responsive at street RPMs, or you build a street engine that's a killer from idle to maybe 5K RPMs. You have to look at dynamic compression ratio, not static C/R....get a good book on big block chevy's and read up on it. I have a dynamic CR calculator if you're interested. You need rod length, cam specs, piston volume, all the details. But dynamic CR is what the engine sees, and that's what's gonna work with your combo, or destroy it.

Johnny, thanks for that info. By the way, I have about 3 or 4 of the Chevy Big Block books and haven't read them yet since I ordered about 10 books right now and reading 5 books for school so no time right now. As soon as spring break hits here I am going to be reading them up like hell. I hear they help a lot and will help me save money when building them too. I am going to try and find a block at the Food Lion Auto Fair at Lowes Motor Speedway here. Is there anything I should look for before I buy besides cracks in the block? I need to find a club around here to join so that way I can get help that way but most of the clubs here are just old guys that hang out on Wednesday nights for an hour or two and then leave and nothing else. I am sure there has to be something here in this city since it's the biggest on in NC.

Originally posted by 76GMC1500
One of the primary reasons for bumping up compression ratios is for that very reason, big cams bleed off cylinder pressure. High compression ratios are more for compensation than they are for power in high rpm engines. The other reason is for better efficiency. Torque is directly related to cylinder pressure and hp is a relation between torque and rpm. If we take a torque cam, they actually develop a higher mean effective pressure than a cam that makes a lot of hp, but they torque cam cannot flow enough air into the cylinders at high rpms to make enough pressure to make any power in those rpms. That's where the big cams with tight seperation angles come in. They can flow more than the torque cams at high rpms, but their mean effective pressures are still lower therefore torque is lower. They do make more hp, though, because the engine is spinning faster.

Well said! I didn't say it wasteh best way to go just that it could be done! 76GMC is correct!