At What Cam Lift Do You Worry About Valve/piston Clearence?

Lift isn't everything, duration and the timing of the cam at low lift will have more issues that total lift. P/V clearance is actually the closest when the valve is open very little.

Mr67Stang said:

I'm looking at a Lunati 235@.050/.540 & 106* L/S in my 351w with manufacturer flycut flat top pistons and World Windsor Sr. 2.02/1.60 cast iron heads. I've never used a cam over .500 lift so I just wanted to ask before I buy the cam.

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Hi,
First off, P/V clearance is critical not so much relative to valve lift as it is to duration, when both valves are open. To better answer your question though, you need to know some basic specs of your rotating assy and piston design. Is your block "zero" deck with those MFG fly cut pistons. Maybe know the CCs of the fly cut, that is, how deep. I'm sure you'll get a number of "hits" with respect to cams and the 351. As we all know, it' always advisable to clay the pistons during "mock up" looking for any issues like "contact".
Not that this is of much help, I'm running TW heads, my cam's duration is 220/234 @ .50 with a gross lift of .570/.562.
My pistons are 4 CC dual relief.
Good Luck with your project.

most ford engines with a valve lift of less than .500" should be good to go in regards to P/V clearance, but it is always best to check. if there is any V/P interference, it is usually in the last 20 degrees of crank rotation where the piston is chasing the valves as they open or close, and it is usually the exhaust valve that has the most chance of interfering.

Mr67Stang said:

I apreciate the input. I guess I am just going to have to clay the pistons as sujested. I went ahead and ordered the cam, new lifters, Victor Jr. manifold, gasket set and threw in a set of slide-a-link traction bars on the order to make that axle behave.

I do not know the CC of the valve reliefs. They are the Kieth Black Hypereutectic flat tops and Summit does not list the volume of the valve reliefs.

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actually you dont have to clay the pistons. if you use a very light spring, just enough to hold the valve in place, and use a dial indicator and degree wheel, you can check the valve to piston clearance just as easily. just turn the crank until the piston is close to 20 degrees btdc, and with the dial indicator zeroed out, raise the rocker arm until the valve hits the piston, and see how far the valve went. do this about every 5 degrees on both valves until you have gone about 20 degrees atdc. you should have at least .080 in the intake and .100 on the exhaust valve.