R16 "stroker" cams

[70MTroadster]

This is directed at Steve, primarily, as he obviously has some pretty good experience with the Stroker engine.

I accessed the engine section and then the cam section on this site. I see that the Isky cam you are running in your stroker has a lift of .350 and a duration of only 228 degrees. The stock cam is listed at 256 duration and 335 lift. The U20 SU engine is listed at 256 duration and .315 lift.

My question is why wouldn't the cam grinders want to approximate the lift and duration of the U20 for a Stroker R16 since the displacement is now the same? AND, why would not duration be increased instead of decreased?

You've told me your engine pulls strong to 6500 rpm, so maybe all of this is mute.........

scott

[S Allen]

Scott,

I cannot be certain in answering your question. The standard grind for an ISKY DR66 is .350 and a duration of only 228 degrees. The machine shop that built my first stroker may have done some fine tuning on the grind. I would forget about the ISKY DR66 and give the guy in Gardena a call. Tell him what you are doing and what kind of peformance you want and I am almost certain he will grind you a cam to fit the ticket. Robert Browne-you out there? Robert had a cam done by them and seems to be quite pleased. Sorry, I could not be more in depth but call the guy in Gardena, CA.

Steve

[70MTroadster]

thanks, I will do it.

[TR]

Hey cam grinding guys,

Sometimes the duration of lift is sacrificed for an increased amount of lift. And given the dynamics of the valve, the true duration is actually more than the geometry of the cam...This is going to be tough to explain without a picture (and I probably have it all wrong), but here goes:

When a cam is ground (modifying an existing cam, making one from scratch is prohibitively expensive), the only way to increase lift is to reduce the diameter of the round part while leaving the nose portion alone. This is because material is only removed, not added to the cam. This decreases the duration because the nose is now narrower. BUT, given that it takes an amount of time proportional to the linear speed of the valve for the valve spring to stop the motion toward the piston and return the valve to the seat...A valve that sees a larger lift typically travels faster, thus takes even longer to close after the cam lobe has passed...This means that a high lift, low duration cam may cause the valve to be open the same duration as a low lift, long duration. All of this extra force, displacement and velocity means increased wear and stress, but the extra travel allows a lot more charge to enter the cylinder during the same (or even less) duration=WooHoo Power!

Hope this is more helpful than confusing and that my understanding is correct! TR

[S Allen]

TR,

Thanks for the in depth on cam geometry-interesting. It makes a little sense to me but I will still leave it up to the real cam grinders.

Steve