Duration vs. PTV clearance
Duration vs. PTV clearance Is there any basic rule of thumb that says something like for every 2 degrees of duration in a cam, you lose .005 worth of piston to valve clearance?
My setup right now consists of 63 cc 243 heads (.010 mill) and I have .130 clearance on the intake. I actually plan on milling a bit further to a total of .024. So theoretically I'll be at .116 from the extra mill. I ALSO am planning on stepping up the cam to about 230/226 on a 112 +4 with 600ish lift (From a 224/224 .563 on 114).
So......If I'm at .116 PTV clearance and add 6 degrees of duration, do you think that will bring me into the sub .100 land of PTV problems??
My setup right now consists of 63 cc 243 heads (.010 mill) and I have .130 clearance on the intake. I actually plan on milling a bit further to a total of .024. So theoretically I'll be at .116 from the extra mill. I ALSO am planning on stepping up the cam to about 230/226 on a 112 +4 with 600ish lift (From a 224/224 .563 on 114).
So......If I'm at .116 PTV clearance and add 6 degrees of duration, do you think that will bring me into the sub .100 land of PTV problems??
Last edited by Xtnct00WS6; Jun 23, 2006 at 04:56 PM.
good question and i am also curious on this.I will quess and say for every two degrees is about .005.I think if you retard the cam some you can gain some clearance,but need to confirm this also.
TECH Apprentice
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Originally Posted by Xtnct00WS6
Nobody knows how much PTV clearance you lose for a given amount of duration in a cam? (for every __ degrees, you have __ less ptv clearance?) Any guesses?
The minimum is said to be .080 Int and .100 on the Exh. so I should be safe. That being said, the only truely safe way to do it is to check it with a dial indicator. All of you cam guys out there feel free to correct any mistakes you see in my numbers. I'm still on a learning curve on this type of calculating and I welcome any constuctive criticism or attaboys. 
