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Discussion Starter · #1 ·
What is the minimum valve to piston clearance on an all motor car? at 0 clearance I have .060 on the exhaust and .088 on the intake. How thin can I cut the piston valve pocket? I need to cut like .060 on the exhaust. I have cp pistons.
 

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How are you checking your piston to valve clearance?

If you are using light "checker" springs odds are you probably have enough clearance... Put the "real" valve springs on and check your clearance.

If you are using the actual valve springs and do have to mill I would call CP and ask them the minimum thickness they suggest...

I had to mill a set of pistons earlier this year to gain some clearance and, if I recall correctly, the "thickness" in the valve pockets was around .080. This was on a n/a set up with ~12:1 and Ross XL400's...
 

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Discussion Starter · #3 ·
Im using a light spring. Maybe I will try to call cp tomorrow. I will get more clearance with the valve spring? I meant 0 lash in the original post not clearance. it's a flat top 14:1 motor n/a.
 

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you will definately gain more clearance with the "real" springs in there...

I have run intake valves much tighter than what you are at right now and exhaust valves with only .065. This was in a flat tappet motor to 8000 rpm. It made me nervous and I would not do it in someone else's stuff...

CP will tell you how thin you can go in the pockets...
 

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Old school safe was .075 int and .100 exh. With the better valve train stuff available today, belt drives, shaft rockers, better pushrods and springs, I was told I could get by with .050 on the intakes and .060 on the exh. I cut the pistons some and came up with .070 intake and .085 on the exh. RM
 

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I am with Real McCoy and use old school numbers .075 int & .100 ex @ 0.0 valve lash.
Remember the cam is pushing the intake valve open during the closest pv event and the spring is trying to close the exhaust valve during the closest pv event.
 

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You said you are doing them at 0 lash. So once you set your valve lash you will gain even more clerance. So if your cam calls for say .020 lash on the exhaust you would also add that to the numbers you have already. Im sure someone will correct me if im wrong.
 

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Good rule of thumb to remember is that the intake valve is chasing the piston, and the piston is chasing the exhaust valve in your min PtoV...

I think the above are good recommendations. There are always cases where less might be needed, or even more might be needed, but these are good rules of thumb.
 
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