Thread: 305 cam advice needed

Tweet

It all comes down to cranking pressure on available pump gas. Please read this explanation from Crane......

Why is it necessary to know the Compression Ratio of an engine in order to choose the correct cam?

The compression ratio of the engine is one of three key factors in determining the engine's cylinder pressure. The other two are the duration of the camshaft (at .050" lifter rise) and the position of the cam in the engine (advanced or retarded). The result of how these three factors interact with one another is the amount of cylinder pressure the engine will generate. (This is usually expressed as the "cranking pressure" that can be measured with a gauge installed in the spark plug hole.)

It is important to be sure that the engine's compression ratio matches the recommended ratio for the cam you are selecting. Too little compression ratio (or too much duration) will cause the cylinder pressure to drop. This will lower the power output of the engine.

With too much compression ratio (or too little duration) the cylinder pressure will be too high, causing pre-ignition and detonation. This condition could severely damage engine components.

How does Cylinder Pressure relate to the octane rating of today's unleaded fuel?

In very basic terms, the more cylinder pressure we make the more power the engine will produce. But look out for the fuel! Today's pump gas is too volatile and cannot tolerate high compression ratio (above 10.5:1) and high cylinder pressure (above approximately 165 PSI) without risking detonation. Fuel octane boosters or expensive racing gasoline will be necessary if too much cylinder pressure is generated.

I tend to lean on the manufacturers to supplement my own experience when I'm looking for information about a combination of parts on a project and also when advising others about component selection. And I tend to be very conservative when I'm spending YOUR money.

You don't want to put too much cam in a motor for a daily driver unless you want to also intall a numerically higher gear and a converter rated at a higher stall speed. Matter of fact is, the first cam in any grinders catalog is probably the best choice for a daily driver. I might go with something like this for a mostly stock 305 that will see some towing duties....
http://www.cranecams.com/?show=brows...tType=camshaft

It's ground on a 112 LSA, so idle will be smooth with good low-end torque and it'll produce good vacuum to drive accessories like power brakes.