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Old 09-05-2013, 07:55 AM   #1
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Default Bore size question

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?
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Old 09-05-2013, 10:37 AM   #2
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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.
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Old 09-07-2013, 12:35 PM   #3
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No one actually knows about this?
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Old 09-08-2013, 12:53 PM   #4
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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.
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Old 09-08-2013, 10:28 PM   #5
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Thanks, will do that.
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Old 09-08-2013, 10:50 PM   #6
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3.330"
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Old 09-08-2013, 10:51 PM   #7
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Quote:
Originally Posted by triple88a View Post
3.330"
3.330 what?
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Old 09-08-2013, 10:51 PM   #8
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Cylinder size.
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Old 09-08-2013, 10:54 PM   #9
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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
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Old 09-08-2013, 10:55 PM   #10
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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.
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Old 09-08-2013, 11:00 PM   #11
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Quote:
Originally Posted by HHammerly View Post
Got a set of pistons and rings for sale if you are going with 9.5 comp ratio
New Supertech pistons pins and rings set - Miata Turbo Forum - Turbo Kitten is watching you test compression.
Those 83.5mm pistons will be mighty lose in his 84.5mm bores!
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Old 09-08-2013, 11:07 PM   #12
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LoL we're talking more than a 32th Would probably sound like an old school diesel.
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Old 09-08-2013, 11:30 PM   #13
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Quote:
Originally Posted by stefanst View Post
Those 83.5mm pistons will be mighty lose in his 84.5mm bores!
Brain fart, 1mm off
Sorry
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