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· Resident Ford Nut
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Discussion Starter · #1 ·
I've never thought about it; what determines the opening and closing events of the valves on the cam card? IE set intake opening at 28* as opposed to 34*. I'm assuming it has the do with the Crank/piston position to achieve max cylinder pressure or some other thing, but what determines it ? :)bulb

You can retard or advance the cam to move the power around but for the most part doesn't the power stay about the same you just move the rpm. At some point though I guess the Cylinder pressure will drop off and you'll lose power.

I figure someone here would know, even if Straub doesn't see this.

Sleeper CP :D
 

· Resident Ford Nut
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10,033 Posts
Discussion Starter · #3 ·
Not lobe sep. but a cam card may read : intake opens at 27* BTDC Closes 70* ABDC Exhaust opens 77 BBDC Closes 26* ATDC. That's part of lobe sep.

The question is, what parameters are used by the cam grinder to determine the desired opening point as far a degreing in a cam. You may need to advance or retard your cam a few degree's to match the cam card. Why is it desired to open the intake at 27* as opposed to 24* or 32* BTDC ?

I hope that makes sense :)bulb

S CP :D
 

· Resident Ford Nut
Joined
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10,033 Posts
Discussion Starter · #6 · (Edited)
Thanks GN-7,

You are correct it's just a function of math. I was just asking for personal reference.

A cam with an intake duration of 280* at .050 and a lobe sep of 114* would have an intake opening point of 26* if ran straight-up.

280/2 -114* lobe sep= 26*

I just wanted to know how that number was derived, now I know. And then there's the deal with the cam having max lift at peak piston velocity,roughly 70-75* crank rotation or when the big end of the rod is at 90* to the crank. Blah, blah, blah.......

S CP :D
 
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