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Old 01-29-2013, 11:15 AM
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You do not pick a camshaft solely by what the compression ratio.
Pick a cam that will do the job you want the motor to do.
Pick the cam duration based on the rpm range you want the power to be made at.
Then pick a compression ratio that is usable with the intended fuel.
Obviously if you limit the fuel choice to a low octane 87 octane then you need to go easy on the engine compression ratio.
just remember low compression ='s low torque output.
A high performance engine needs a high performance fuel.

For a high performance pump gas motor using a 92 octane fuel a compression ratio of 9.8 to 10.5:1 works
real well. And the cam , from that point, does not have that much effect on that.
On pump gas, once you get beyond about 10.5:1 cr your chance of having engine knock problems
greatly increases, reguardless of what cam is in that motor.
You want a generous compression ratio, but not excessive for the fuel in the tank.
More compression ='s more engine torque output. Up the the practical usable limit of the fuel in the tank.
Beyond 10.5:1 compression consider it EXPERIMENTAL, as you are at or real close to the practical street operational edge of GOOD pump gas.
10.6,,,10.7 +++ expect that the motor may/probabily will want more fuel octane that wahts in the pump.
Allowing he engine to ping and knock because the cr is too high for the pump gas fuels ability to resist detonation ("octane"), will result in engine damage. Its just a matter of time.
Just realize a cam cannot be a big cam and be a small cam a the same time.
Pick a cam based on how you will really be using the vehicle and the gear ratio.
Gear ratio:
Placeing or establishing the RPM @ 60MPH ("cruise rpm') is a good bench mark.
Auto trans:
Bigger cams need a high stall too, especially in a small cid engine.

Intake manifolds. If you want a powerfull 307 then a RPM manifold and 750cfm carb is great choice.
That same motor will want a cam and gear and a converter too.
If you area after big horsepower do not dummy it down with low horsepower parts or a small carb.
A 307 makes (more) power like any other motor, By breathing more air and processing more fuel.
Yup it will need rpm.

But of you do not want a big horsepower, and want a low rpm , stock like cruiser, then keep the cam small
and use a low end torque type intake manifold.
The RPM manifold and others (dual plane hi rise) like it that have a full plenum divider have broad power range.

If you want to cam it up for power, you want stiff gears. ( A 3307 is much like a 283 or 327, it likes RPM, when hot rodded.
If you are not willing to do that, keep the cam for your 307 relatively small.
Like stated you don't really want or need a 2.02" intake valve for a 307. A 1.94" valve gets it done.
Especially when the head is ported for improved air flow. Flow is power. A 1.94 x 1.60 valve set is ideal for a high perf
street 307. A 1.94" x 1.50" valve set gets it done too.

Last edited by F-BIRD'88; 01-29-2013 at 11:42 AM.
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