Valve to piston clearance?

nm9stheham said

Understood and agreed 100%. When I gave a number to the OP, it was qualified with the remark that, whatever clearance was figured at TDC, it normally would get tighter after TDC. So if things were already too tight at TDC, it would only get worse.

BTW, so everyone will know, the above graph is computed from a spreadsheet, and is really just for illustration only. The piston height vs crank angle is a formula that is is easy to program in. The cam profile info is what is needed, plus some other measurements to compute this with ANY degree of confidence or accuracy.... Getting the cam's detailed profile info is not something you get off of a website! Makes it hard to predict P-V clearance in advance, as the OP asked.

So that is the value of buying pistons with goof valve reliefs if you are going to get some lift going.

Click to expand...

It just goes to show what a black art cam lobe profile really is.
Regarding the Pistons, well I guess the custom manufacturers have realized that a guy who orders a piston with say 13:1 compression is probably not gonna use a cam with .500 lift so we better give him the appropriate valve relief. This was my first time ordering a custom piston. Ross walked me through it and it could not have worked out better. It was mentioned earlier in this thread about having the Pistons before going to the machinist so he can fit them correctly.
In the past my local machinist and I have always done it that way.
But not this time. Ross told me what the bore size will need to be and the proper piston to wall clearance is designed by Ross into the piston. We still waited to get the Pistons before we started, but the Pistons were exactly what Ross said and proper clearance was obtained right at the nominal bore size that Ross said. Kudos to them.