2manyhobyz

iTrader: (4)

I was having trouble getting a straight answer from the piston companys. They wanted to sell me a custom set. I thought I heard the valve angles on the 99-00 head are different so when you have 1mm oversize valves there might be contact issues. I'm sure there are people who are running this head set up. What did you use? Also, are you running the head with stock cams or more lift?
I also cc the head tonight and found that stock combustion chamber is 50cc. The Supertech head is more like 49.5.
Thanks,
-JB

miata2fast

iTrader: (2)

??? You mean a head with Supertech valves? I could see that as the larger valves would take up just a tad bit of volume because of the larger diameter. If you had the valves sunk, the volume would go up.

As far as the valve angle goes. The 99 and newer head has the same valve angle as the older head. The only real difference in the design is the fact that the intake runner has been raised significantly.

Most piston manufacturers make the valve pocket wide enough to clear oversized valves and deep enough to clear larger lift cams. However, it is up to you to check your clearances to be sure that they are sufficient. You will most likely not have problems with the common popular pistons.

I had a problem with a set of JE high compression pistons that I had purchased quite a few years ago that did not clear my oversized valves, when I changed to a modified 99 head. It was very close, and I was able to clear the pockets with aggressive grit sand paper and a little time.

I was very suprised that JE would not have made pockets wide enough to fit larger valves, but I guess at the time most racers were not using larger valves when the pistons were made.

So yes, clearance problems could happen, and if you are running anything exotic, your chances of problems go up. Those problems can be corrected however. Just be sure you check everything.

NiklasFalk

iTrader: (1)

VVT head, ST 11:1 pistons, ST +1mm intake valves, block decked flush (0.7 mm IIRC), 305 cams lifting 10.7mm, head skimmed somewhat:
Measuring without the head gasket to compensate for rod stretch revealed that I have to reduce the VVT movement to prevent contact, but only to 38 degrees.

So I would assume that the ST pistons have enough clearance for almost all situations.
Cams with more duration would require more care of course.

The pistons were however massaged a bit to smoothed the sharp edges, so this could have improved the clearance a bit, but very minor.

my97miata

I plan on doing the same head, a 99 with +1mm Supertech valves. But I will be using the BP-5A (MSM) intake camshaft on top of a stock 97 bottom end (9:1 CR). I seriously doubt I'll have any clearance issues with such a set-up.

2manyhobyz

iTrader: (4)

Thanks guys, I'm not sure if I'm going to go with with Supertech or Wiseco pistons (8.5:1). What started all this is that Wiseco says no for their pistons and the 99 head. I don't know if that's incorrect information at this point. Is that why Flyin Miata had to have custom ones made for them ($$$)? So It would be good to find someone who's running that setup.

GTurbo

iTrader: (1)

I know at least one member on here thats running 10.5:1 Wiseco pistons with a 99 head. here's a link to his intro post (https://www.miataturbo.net/meet-gree...eetings-55401/) so Wiseco claiming to not recommend running even lower compression on that head is odd. Sounds to me like Flyin Miata drilled an extra hole in weiscos and marketed them as their own piston but thats just my on that

stefanst

iTrader: (1)

I have the +1mm Supertechs on a 99 head with stock cams on a stock 97 bottom. No clearance issues. Not sure what the BP-5A would do to it, but doubt it would matter.

2manyhobyz

iTrader: (4)

So I talked to Wiseco and was asking if I ordered their 8.5:1 pistons and If I Installed them to test fit the the clearance (Clay the Head). "You put them in, their yours". It's not like I'm gonna start the motor. It was pointed out that 8.5:1's should have even more clearance having more dish in the pistons. Has anyone measured the valve angle between a 99-00 head and a 94-97. I'll try to post the 99 head later today.

2manyhobyz

iTrader: (4)

OK, went out to the garage and pulled out the 4ft level. Found a couple of sockets that were the same size as the valves. For finding the angle I used the Johnson brand Magnetic Angle Locator. Both intake and exhaust are 25 degrees. I realized a little later that you could just rotate the cam until the valves stick out, same reading, 25 degrees. So, anybody have a non 99-00 head they can find the valve angle for comparison?

miata2fast

iTrader: (2)

They are the same.

2manyhobyz

iTrader: (4)

Thanks Troy,
That's good to know they are the same angle.
A related question, how do piston manufactures achieve their piston to wall clearance?

GTurbo

iTrader: (1)

You mean how to they determine them?

Thermal expansion determined by silicone content of the alloy. More silicone = less thermal expansion. I'd imagine they mic the pistons cold, mic them again after heating them to normal operating temperatures.