cam timing article

by pila Wed Mar 19, 2014 9:34 pm

An article in Hot Rod Magazine about timing a cam is interesting. The article is about what happens to compression when the cam is advanced or retarded. The article mentions that performance cams are generally ground 4 degrees advanced. They way it suggests getting the best compression ratio ( actual ) is having one cylinder put together in the block, and having a starter mounted to turn the crank, to check compression ( in lbs ) at different advance or retard settings on the cam, to get the highest compression number, while looking for the optimum compression etc..
Of course setting is advanced, to some degree, closes the intake valve earlier, making the compression stroke event start earlier, to get more volume pushed into that stroke, etc.
Maybe I'll try that on the next Chevy I build for my Malibu, just for curiosity Very Happy

by bracketchev1221 Thu Mar 20, 2014 7:19 am

pila wrote:An article in Hot Rod Magazine about timing a cam is interesting. The article is about what happens to compression when the cam is advanced or retarded. The article mentions that performance cams are generally ground 4 degrees advanced. They way it suggests getting the best compression ratio ( actual ) is having one cylinder put together in the block, and having a starter mounted to turn the crank, to check compression ( in lbs ) at different advance or retard settings on the cam, to get the highest compression number, while looking for the optimum compression etc..
Of course setting is advanced, to some degree, closes the intake valve earlier, making the compression stroke event start earlier, to get more volume pushed into that stroke, etc. Maybe I'll try that on the next Chevy I build for my Malibu, just for curiosity

On a related note, on a solid lifter cam you can play with the valve lash to change the cam timing events somewhat to change cranking compression as well. Closing up the valve lash opens the valve earlier and closes them later, making the cam duration longer. Opening the valve lash does the opposite. This can help you diagnose if the cam is too large or too small. With a solid, it is important to note though, it is ok to tighten the lash almost as much as you want to. Opening the lash, is not really recommended to open more than .004 from the cam card because the lifter can get away from the opening and closing ramps of the cam and cause damage to the cam. I did a cranking test on my 540 before it went to the dyno and I think it cranked at 205-210. The cam grinder recommended a .003 open on the intake and leave the exhaust alone. On the dyno, this change was worth 4-5 hp.

by pila Thu Mar 20, 2014 10:23 am

Interesting stuff Ray. Thanks for that Very Happy

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