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Discussion Starter #1 (Edited)
Need help i have been told yes and no i have a comp cam .555/.570 lift on my car duration i think 280/288 114 lobe separation i want to install some heads with valve size 2.02/1.60 bottom end has stock pistons will Valve hit the piston cause of the size of the cam?

Thank you ,
 

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No one can give you a for sure answer, if they do, they are idiots. To many varibles effect Piston to valve clearance. Only way to find out is to Clay or use the drop valve and feeler gauge method. But on a stock style piston, with stock valve placement heads, you will more than likely have to Notch the valve relief to accomadate the 2.02 valves larger radius.
 

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Per the village idiot.....

I would guess your not going to clear it without replacing the stock pistons with dished or flat tops with valve reliefs notched in. I am going to stick my neck out and possibly be an "idiot". I highly doubt you will have the clearance. I am almost sure you won't.

That is a huge amount of lift compared to stock. (stock .444) around 25% more lift. Not to mention larger valves. You can do exactly as 89Coupe said and use the clay method. Just does not sound "realistic" to put that huge of a lift and that large of valves and have no clearance issues with a stock set-up. Why not just throw in some forged pistons while you have it torn out anyways?

I used forged pistons with valve reliefs notched in the top, with a .542 lift. X303 cam.

Good luck, let me know what you find out after testing the theory. I am curious.
 

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Please explain 89Coupe

No one can give you a for sure answer, if they do, they are idiots. To many varibles effect Piston to valve clearance. Only way to find out is to Clay or use the drop valve and feeler gauge method. But on a stock style piston, with stock valve placement heads, you will more than likely have to Notch the valve relief to accomadate the 2.02 valves larger radius.
What are the variables that effect piston to valve clearance? How is the math different from one stock motor to the next? Is it the Variable of the heads themselves?

Just curious:scratchchin
 
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are you planning on using 2.02's with a stock bore 302

if so you will have another problen to deal with......
 

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Actually what I meant was that if someone tells you that you wont have any problems, they are idoits.

One stock motor may have the pistons slightly above the block deck, than another. head deck hieght can vary from one set of heads to the next. Milling heads has a direct effect on PtV, as this move the valves closer to the piston.

Total lift has nothing to do with PtV clearance, as the piston is heading away from the valve. On the exhaust, the piston is at the bottom of the cylinder and it chases the Exhaust valve till the valve closes. Thus why the exhaust, usually needs more Clearance For PtV.

The overlap is the most critical point for PtV clearance. As the piston is at TDC and both valves are slightly open.
 

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It is impossible to say anything without knowing the type of heads you have and a half dozen other things.

Out of everything, maximum lift is just one small part of the problem. .050 duration is almost meaningless. It is when the piston catches the valves, and that is usually when the valves are over .25 inch off the seat, that really matters.

You better use some clay and some check springs and test it if you aren't sure. With 16 valves waiting to get bent or 8 pistons waiting to be trashed, a public opinion poll is not the way to go.

Tom
 

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Discussion Starter #10 (Edited)
Thanx every1 for your info on this issue i guess i might just leave it as is 4 now. :bigthumbsup was also thinkin the same thing but u knwow thiers a couple of ur buddies sayin yes they fit but oweell till next time untill I finish my other block.

Thanx
 

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I understand now!

Actually what I meant was that if someone tells you that you wont have any problems, they are idoits.

One stock motor may have the pistons slightly above the block deck, than another. head deck hieght can vary from one set of heads to the next. Milling heads has a direct effect on PtV, as this move the valves closer to the piston.

Total lift has nothing to do with PtV clearance, as the piston is heading away from the valve. On the exhaust, the piston is at the bottom of the cylinder and it chases the Exhaust valve till the valve closes. Thus why the exhaust, usually needs more Clearance For PtV.

The overlap is the most critical point for PtV clearance. As the piston is at TDC and both valves are slightly open.
Thanks man, that makes a lot of sense. I never knew that the stock motors varied like that. Did know obviously that machining the heads or block takes away, but honestly did not even think of it.

Always good info 89Coupe :rockwoot:
 
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