+1mm valves & 10:1 CR clearence questions
 

Looking for some valve clearance data from those who have run the 10:1 stock pistons with +1mm valves on 99 head.

I am trying to get a rough idea what kinda cam lift I can get away with.

well im running +1mm valves on 9:1 pistons. I dont know who your piston manufacturer is but im gonna assume that the valve pockets are gonna be cut to the same depth on all miata pistons by that manufacturer. The material around it is what creates the change in compression.

If that is true, I am running .490 lift and 295 duration on my intake side with no modifications to the piston. But the only way to know for sure what you can run, is to assemble one piston in the engine, clay it up and check your clearance.

PM miata2fast about it. He has 12 to 1 with 1mm oversize valves and a larger cam in a 99 head. He did have some clearance/contact issues and could shed some light on the subject.

With the 10:1 wescos, a block and head that hasn't been machined too extreme and the +1mm supertechs....my motor is still non-interference. I clayed the motor when I built it and measured the actual clearance but don't have my notebook with me....but I think I stil had something like .060" all the way around.

i would be more cautious with big dome pistons, but a 10.0:1 is gonna be flat top if i had to guess, the valve pockets should be just as deep as a 9.0:1, But every piston manufacture will be different and cams change alot as far as open and close timing. And head and block machining can change alot too. my pistons are around .003 in the hole and my head was cut .010"

These are the supertech 10:1 that are a copy of the stock 2001+ 10:1 piston.

Thanks will do

Yeah, if I recall, he had almost enough depth with the valve reliefs but they weren't cut with a large enough diameter for the oversize valves. He had a bad day. But, yes, definitely ask him for details including piston brand and cam lift info. I know he is running some pretty big cams compared to stock.

My camshaft is actually pretty mild, with lift not much bigger than a stock 99 cam.

The valves touched the corners on the valve reliefs on each piston's intake side. The valve reliefs were not cut large enough. I simply made the reliefs larger with sandpaper. Ironically there was no visible damage to valves or cylinder head. I think some valves were slightly bent, but they were all repairable.

Pistons were JE, but I bought these pistons years ago, and obviously JE has since made a change to the valve reliefs.

Really should clay it. Unless you use the exact same cam as someone else recommends, timed exactly the same, you're shooting in the dark. We have built a BP4W head with OTS Supertech 85.5 11.0:1's cut down to about 10.5:1 with .425 lift ~280°. YMMV.

I will clay the pistons and determine safe cam adjustments before it all goes together.

I am just looking for overall input on stock size valve reliefs with 2001+ 10:1 pistons with +1mm valves. Knowing the pockets are smaller than than most aftermarket pistons I am trying to get an idea of potential troubles.

The real struggle is hearing Andrews voice telling me to go VVT.

Bringing this back up just in case anyone is looking for info in the future. I was running +1 intake/exhaust valves with stock 10:1 pistons and rebello racing regrinds. .385" lift and ~216 duration on intake and exhaust. Went up to 38 degrees advanced on the vvt and never had an issue.

With 99 head. +1mm valves and .396 lift / 216 duration at .050 cams we had to notch the pistons more using the 10:1 stock style pistons.

I had the block zero decked and the head shaved some so maybe that's why you were safe and I was not. It could also be the cams themselves. The ones I used have very aggressive opening ramps.