Valve to piston clearance?

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dartfreak75

Restore it, Dont part it!
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Ok I have been doing alot of reading and research on this topic and everything I see is how to check it after the engine is already assembled. Is there any formula or calculations to check and make sure you will have adequate clearance before you start buying parts? For example I have a piston a goal compression and a cam chosen that I want to use how can figure out if it will work without buying it and test fiting it?
 
General rule of thumb is .080" on the intake and .100" on the exhaust. As for the best way to figure, physical set up and measuring with clay.
 
General rule of thumb is .080" on the intake and .100" on the exhaust. As for the best way to figure, physical set up and measuring with clay.
Thanks I knew the general min and I have found tons of info on how to measure it. Just seems like there has to be a way to calculate it before you start buying parts.
 
how can figure out if it will work without buying it and test fiting it?

You don't, as already stated you have to test fit and measure........it's part of the fun building process

A thought........buy a CAD program and do a design analysis
 
In that case Hopefully I can find someone here with a similar setup as mine and get some info from them.
 
You could mock it up with an old cam, that would give you an idea of how much clearance you have.
 
Does any one here run a 318 with flat top pistons around .03 under the deck??
 
You are going thru some of the same thought processes as me. I am planning and getting parts for a street 390 build. Trying not to buy the wrong stuff, etc.

Don’t overthink this part. If you make sure you have the right compression height pistons and you get a reputable cam. You are 99% of the way there. You need to mock it up once you have everything but chances are that you will have more space than you want and you will need to take off some from the deck. Especially with if you are going to use a mopar head. Those are just my thoughts, I am a rookie.
 
Piston manufacturer usually states max valve lift. Go to there web site and look.
 
flat top pistons with or without valve notches? have the heads been cut? head gasket thickness? valve sizes? there are too many variables involved-that is why we do not have a formula for small block mopar engines.
 
It is not max lift that cause problems...the piston is way down in the bore then...it is during the overlap period where the exhaust closing and intake is opening...
duration...LSA and retarding or advancing the cam all change the valve to piston clearance..
 
OP, maybe describe the pistons, milling, decking, and that cam you have in mind, and someone might be able to relate their measurements for a similar setup.

I have a spreadsheet for piston position versus crank angle. But the details of cam lift versus crank angle would be needed to work this on paper, plus a direct measurements off of the head for how far the valve sits above the head surface when closed.
 
The build combo in mind is a 318 bored .040 over with h814cp speed pro piston it's a true flat top no relief cuts the block will be cut .037 to get the piston. 030 in the hole. I will be using a regular felpro blue gasket (.04-.045) the heads will be cut around .005-.01 just enough to clean them and make sure they are flat.
The heads are 302 heads with std sized valves and this cam. And the cam will be set straight up dot to dot. No additional advance

Screenshot_20181122-053907_Samsung Internet.jpg
 
I would put that together and not even think twice. The duration is what you have to worry about, not the lift when concerned with interference issues and that cam doesn't have anywhere near enough duration to worry about.
 
I would put that together and not even think twice. The duration is what you have to worry about, not the lift when concerned with interference issues and that cam doesn't have anywhere near enough duration to worry about.
Thanks rusty!! I appreciate your help that is a huge relief. Iv been up reading and studying about this since about 5 am lol
Do you think that will be a pretty combo?
 
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