PTVC question. Someone please try and explain

Stumbaugh

Member
May 13, 2010
903
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19
Russellville, Ar
Ok, I have been doing some research about putting cam's in my car and have read a little about Piston to Valve clearance issues with the 99-04 2v's. Here's my question;

Some people are saying that the biggest cam you can run with out notching the piston's is a .500 lift cam, but then HiTech is saying there are no PTV issues with their cams. But then someone on here says there is only .001 clearance with the HiTech cams, but I have personally saw 2 or 3 people run the CMS stage 2 cams (which are bigger than Hitech's) and not get their piston's notched and have no issues. How is this possible?
 
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trinity_gt

10 Year Member
Jan 31, 2003
3,125
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99
Canada
Peak lift isn't usually the problem since peak lift generally occurs with the piston some ways down the bore. A limiting factor to lift is springs and potential interference between the retainer and the seal at maximum lift.

For PTV the issue is how far off the seat the valve is when the piston is at or near TDC. This is where the installation angle, duration and the shape of the lobe matters. My fairly mild Comp 262AH cams have 0.550 lift and I have no PTV issues. However, these are mild cams with not a lot of duration.

I don't think there's one single answer. A vendor can grind his ramps to help alleviate the chances of PTV but if you're going with any sort of "aggressive" cam the onus really is on you to verify for yourself that at your installed angle (degreed straight up, advanced, retarded etc), there's adequate clearance through all four strokes. This generally means using clay on piston crowns, installing the heads with pre-compressed head-gaskets, turning the engine by hand and analyzing the thickness of the thinnest part of the impression. Off the top of my head you'd want something like 0.050" minimum on the intake and 0.090" on the exhaust though I'm sure others will supply different values. Certainly, you want more than 0.001" :)

YMMV...
 

nickmckinney

Member
Sep 25, 2009
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16
www.modularheadshop.com
Max lift and ramp speed have nothing to do with it with any of the cams for these motors. The intake valve is closest to the piston at 5-10 degrees ATDC and the cam lift is in the 0.1-0.3" range. Only thing that affects PTV is the cam duration and install centerline (how advance or retarded)