I don't have a 99 head lying around. The VVT intake cam supposedly has more lift.

The c/r of the pistons shouldn't matter because the depth and location of the cutouts are fixes wrt to the piston pin. The outer edge of the deck of the piston is the same across the different c/r pistons.

 

Retarding the cams = more clearance, advancing = less clearance.

 

I have a '99 head lying around, albeit with oversize intake valves. Bring one of your pistons over and we can check it.

--Ian

 

Don't forget V-V clearance if we are talking about higher lift cams. Although on a miata I don't know what lift it would take to ever make V-V contact happen.

 

I wasn't, but the topic was piston to valve clearance. It's usually a combination of lift and more duration that gets you valve to valve clearance issues.

You're completely right though, if I were going to be making larger cams for a VVT engine I'd be checking valve to piston and valve to valve clearance carefully.

 

I just measured them and they are about 0.028" below the deck.

 

Modify the pistons slightly? As a bonus you get an even lower CR.

 

That sounds like a good idea. Just hacksaw off that protruding edge.

 

I was thinking more along the lines of getting an end mill in to increase the depth of the valve reliefs but your way sounds good too

 

Then add a quarter in the middle with JB Weld to get the compression back to 8.6:1.

 

Well if you want, you could go to 8.6.2 so you would have a balanced even ratio. The extra .1 could be gained by jb welding a dime to add the .1. The quarter actually adds .25.

 

A flycutter works better as you can put a larger radius in the base of the valve pocket. The sharp corners a regular end mill leaves aren't radiused enough.

 

You can buy radiused end mills. We refer to them as bull nosed cutters in my shop. I suppose it would be up to whoever did the job.

 

I know... but you can grind a flycutter in a few minutes and not have to order it. You're right though, it is sort of a preference thing. If I was going to be doing a ton of valve pocket cutting of the same pocket size I'd get the mill. For a once in a while thing or if you're doing a bunch of different pocket sizes I'd use the flycutter.

 

Piston to valve clearance with my 8.6:1 84mm Supertech pistons, to standard size intake valves on my VVT head with stock cam, around 3 mm at full cam advance.

 

Sigh, guess I'll want to be checking my wisecos, they aren't FM's... Is there an easy way to tell FM's part number from the "regular" miata wisecos?

The VVT cam does have more lift. I have both heads, but not the pistons handy. I would love to go to a higher lift cam at some point.... Would like to think I'm not going to be in any trouble here. Certainly more pocketing and less compression would work well.

Jason - your measurements are vertical, or in the slope of the valve?

 

3 mm = thinnest point of the lump of clay that got squished.

 

Jason,
I just ordered a set of these last week and from what I have understood from this thread is that as long as I change my timing belt religiously and it does not break I should be fine right?

 

Did you ever find these? I'm just about to plop a head on my motor.....

You and me both. :-) I've got wisecos, but I'm really curious

That's the idea. :-)

I meant when you posted measurements from the ring land down. So I can measure mine.

 

Correct. I think only badly neglected miata motors break their timing belts.