Calculation for Valve to Piston clearance

[66Satellite47]

The cam lobe design makes more difference than the rocker ratio. Remember the piston to valve issue is not at max lobe lift. You do want some extra clearance to play with to move the cam timing around a bit.

 

[451Mopar]

I didn't check the math, but it seems right. It does make an assumption that the valve starts at the same height in the chamber.
Need to know how much the valve opens till it is at the head deck surface. The closed valve distance above the deck can be different for many reasons, like the head was milled, or the valve seats were cut deeper, or the new head has a different chamber design, ....

 

[33 IMP]

I saw a piece that said there were 13 factors that influenced p/v clearance. Calculations only account for a couple. That's why everyone recommends actual measurements.
For what it's worth, we ran a .590 purple shaft in a flat top cast piston 440 with 906 heads. It required only a small divit, maybe .040 deep, probably cause the piston was down the hole a bit. We cut it with a homemade cutter, similar to the Lisle piece.

 

[Doorkicker]

I didn't check the math, but it seems right. It does make an assumption that the valve starts at the same height in the chamber.
Need to know how much the valve opens till it is at the head deck surface. The closed valve distance above the deck can be different for many reasons, like the head was milled, or the valve seats were cut deeper, or the new head has a different chamber design, ....

Interesting you brought that up because that was another point I've been researching. So, I called the folks over at TrickFlow and they said it's as casy, but they're engineering team is send over the valve drop measurements to double check. Nice catch!

 

[toolmanmike]

I measured mine with a indicator on the valve stem, a light checking spring, and the piston at TDC.

 

[33 IMP]

I measured mine with a indicator on the valve stem, a light checking spring, and the piston at TDC.

I measure mine the same way, but I find the exhaust is closest 10° btdc, and the intake 5-15° atdc. Not worried about the radial, the reliefs are plenty large enough in diameter.
Your results may vary.

 

[66Satellite47]

I measured mine with a indicator on the valve stem, a light checking spring, and the piston at TDC.

That will seldom give an accurate reading. I was lazy one day and used that method. Next day walked the both the intake and exhaust up over the lobe checking at 5* increments. The results were very different, nearly .050. It does depend on the lope design, but surely the proper method is needed.