FORMULAVEE.ORG

Just wondering........why do we retard the cam timing 2-4 degrees? Also read somewhere for vintage Vees use stock cam timing, why the difference?

thanks, don

in the begining, we couldn't use off set keys and relied on sloppy gears to retard the cam. Now we use offset keys or adjustable gears. It might be easier to understand if we think of advancing the crank versus retarding the cam. By retarding the cam we start the intake event sooner in terms of crank angle to make up for engine speed. Much like timing, we lead the events relative to the crank angle to time the charge for efficiency at higher rpm. Advancing the ignition timing is the same principle, to allow time for the explosion to reach maximum effect at the optimum crank angle. Hope this helps.

Don,
You also asked about the diff between a "regular vee" and vintage - the vintage guys (mostly) still run a fan shroud and their Max RPM is generally MUCH lower than ours - more like the max of an original beetle - therefore standard (or closer to standard) would work better for them. Retarding the cam to get more power at 6000+, won't do any good for an engine that never goes past 5500.
Steve

I THINK Brians explanation is correct, but I really didn't understand it.

Let me give it a try. At high RPM the engine is drawing in lots of air. This air (especially in our long intake runners) gets "stretched" like a rubber band. With a retarded cam we delay the closing of the intake valve slightly. This allows that "streched" air (that has mass) to still get into the head. This is actually called "supercharging effect". This is why some race engines can achieve MORE than 100% efficiency at certain RPM. There are of course no free lucnches. We sacrifice some low end torque in doing this, but it is in an RPM range where we never operate so we don't care.

Jim

Thanks very much. Always nice to know what is going on behind my head.

cheers, don