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-   -   Pre-planning Valve Relief (https://www.miataturbo.net/engine-performance-56/pre-planning-valve-relief-93328/)

dan91 05-22-2017 10:39 PM

Pre-planning Valve Relief
 
I am building the bottom end of a VVT engine now, and in the future (2-3 years) I would like to go to larger valves and a stronger cam. Before then, the engine will be turboed. Therefore, I would like to cut the larger valve reliefs in the piston necessary now, before the engine is all reassembled and in the car. I can't seem to figure out how to do this.

From what I have read, the process is to take a valve and cut the head off, then lathe it down to a point. The sharpened valve stem is then slid into the normal valve guide, and the piston is moved to some number of degrees before or after top dead center (10?). The stem is given a whack to mark the piston, which gives the center of where the valve relief should be cut. The valve relief to be cut should be the diameter of the new valve plus some amount (0.2 inches?)

Have I got this right so far?

The harder part is the lift. I've been trying to find the stock lift on VVT cams, and I'm planning ahead for Tomei cams, which are Intake: 0.425" lift and Exhaust: 0.393" lift. If and when I find the stock lift, do I just subtract the Tomei lift from the stock lift and cut the reliefs that much deeper? For example, if the stock VVT exhaust is 0.350" lift, and Tomei is 0.393", I should cut the valve pocket in the piston 0.043" deeper?

Does anyone know the stock VVT intake cam lift?

I'm using Supertech 9:1 pistons. Does anyone know how deep the reliefs can be cut before getting into structural issues?

Anyone have a burnt up valve they feel like mailing my way? I'm in Chicagoland.


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