SC cam upgrades -- spec comparisons
 

I have tried to provide a measure of the difference of the changes of the aftermarket grinds compared to the stock:

________Lift____________Duration (*)
Cam_____Intake__Exhaust_Intake__Exhaust
20/21___0.485___0.452___238_____226
964_____0.464___0.426___236_____226
SC _____0.455___0.402___229_____220

________% Difference
20/21___7_______12______4_______3
964_____2________6______3_______3

I know that the 20/21 web cam is a favorite, and it is more aggressive that the 964 grind. Given that the intake duration is quite close, 236 vs 236 deg, that seems a considerable difference in intake lift. Can this be translated as: for roughly the same amount of duration, the 20/21 grind is snapping the intake valve that much more travel, possibly leading to earlier valve train failure? On the intake side, the ratio of the difference is > 3:1 (.03" total), whereas on the exhaust side it is a closer 2:1.

I haven't seen the gains in HP/torque between the cams, with the proper free-flowing exhaust header/muffler combination of course, but I am curious what benefits folks are getting from the web cams compared with the durability of their valve trains. Is driveability really okay, including low-end response, with the 20/21 web cam grind?

Thanks, John

(*) Data are from Web cams, and B. Anderson's specs are slightly different.

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'78 911 SC 3.0

[This message has been edited by hilandscott (edited 09-26-2001).]

[This message has been edited by hilandscott (edited 09-26-2001).]

I doubt very seriously that you have anything to worry about in the valve train at the low revs SC engines turn. Take a look at the specs for the SC RS engine in BA's book if you want to see what your valve train is capable of!

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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler