Given a cam's duration at .050 can you calculate advertised duration(.006 or.004)? The reason I ask is b/c I'm throwing around some ideas for a custom grind. I have an idea of what sort of duration I want at .050(226/232), but I need advertised duration to calculate valve events and DCR, right? So far I'm thinking 226/232 .570/.580 112 LSA. Could I calculate advertised duration, valve events, DCR and rpm range with only this information? Thanks!

 

Since you haven't had the cam ground, you should call whatever company you intend to get the cam from. Who were you thinking about? If you talk to them, they'll tell you what the advertised durations are. Usually they have set lobes to choose from, so lift will not be as specific of a choice as duration can be. Most cam companies use 50-55 more advertised duration (.006") than duration at .050, but that would only be an estimate.

 

I'm talking with John at Futral, but he's not in today.

 

Futral gets all of his cams made at Cam Motion. They use about 54-55 more advertised than @.050". The Comp Cam XE lobes use anywhere from 54-62 with most closer to 55 or so. The lower the difference, the higher the ramp rate and more power you'll make. A smaller difference will also be harder on the valvetrain.

 

What's the difference b/t duration at .050 and .006? I don't understand! How exactly does a lower # equal more aggressive ramp rate?

 

There's a lot of math in it. Let me find some good reading for you. The smaller the difference between the advertised and @.050" duration, the more agressive the lobe, I know that for fact.

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