I was measuring the block bore yesterday and got:

Piston 1
X 3.327in (84.51mm)
Y 3.327in (84.51mm)

Piston 2
X 3.327in (84.51mm)
Y 3.326in (84.48mm)

Piston 3
X 3.327in (84.51mm)
Y 3.326in (84.48mm)

Piston 4
X 3.327in (84.51mm)
Y 3.327in (84.51mm)

Do you guys recommend that I should bore the block? If so, what size? If not, what size pistons should I use and what brand?

 

You're already 1.5mm over stock. AFAIK there isn't much more meat left to bore. Some people go to 85.0mm, but that's it.
If you get 84.5mm pistons you have .01mm (0.004") clearance that's not too bad. In fact that's what I asked my machine shop to do for me. So if the cylinder walls look good remove glazing, slap in new pistons and go.

But I'd definitely wait for one of the more experienced guys to weigh in too.

 

No one actually knows about this?

 

Sorry- made a mistake in my earlier post. I usually get the numbers right, but the order of magnitude wrong. 0.004" is 0.1mm, not 0.01mm!

You're sitting almost exactly at 84.50mm. You want your bore to be 0.05mm to 0.1mm larger than your piston- depending on your manufacturer's specs and your application.

If your bores look good, buy some 84.5mm pistons, measure them and then have the block machined to fit. If they need to remove less than 0.1mm, my guess would be that honing would be sufficient.

 

Thanks, will do that.

 

3.330"

 

3.330 what?

 

Cylinder size.

 

Got a set of pistons and rings for sale if you are going with 9.5 comp ratio
https://www.miataturbo.net/showthrea...82#post1046782

 

Wait my bad i thought you were talking about those piston sizes being "piston size" and not the cylinder size of the block.

4 thao clearance is right at the upper limit.

 

Those 83.5mm pistons will be mighty lose in his 84.5mm bores!

 

LoL we're talking more than a 32th Would probably sound like an old school diesel.

 

Brain fart, 1mm off
Sorry