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Old 04-18-2012, 04:22 AM   #1
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Default can't decide which pistons

I'm in the middle of waiting for parts to come in for an engine rebuild, but I'm having problems deciding which route to go

Planning on semi daily driving the car when it's nice, plus autox and maybe a track day or two. turbo obviously

Route 1: 8:6 supertechs .020 overbore with forged rods and go all out with balancing, etc. at a machine shop spending da monies....

Route 2: Topline standard pistons with forged rods. Engine cylinder walls are in good shape, but will obviously get a hone and a good cleaning if I go this route. Would be trying my hand at balancing pistons and rods myself with a digital scale/belt sander. Budget build

Obviously money is a factor, but I want something that will last. Do I go all out with the supertechs? Thing is, I actually ordered the pistons already. Rods are on their way to me too. Worried about DDing the car and having to warm up the thing carefully every time I drive it with the forged pistons, or do I go Topline and worry about it on the track? ugh, can't decide
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Old 04-18-2012, 04:29 AM   #2
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OPtion 1. forget the balancing, just check the piston weights yourself.
Cranks are generally well balanced from the factory.

NO need to warm up car, Supertechs use lower expansion alloy which run tighter clearances. Just drive extra gently til the coolant is hot.
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Old 04-18-2012, 11:45 AM   #3
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On either build, at a minumin, do a half balance, Rods and pistons.

As Jason said, most cranks are fairly close from the factory.

Pay close attention to your ring gaps, and Piston to wall clearance.

Going an extra .0005-.001 clearance on the PTW clearance, will not give piston slap, but will give you a tad more when you go hammer it for extended periods of time.

Adding an extra .001-.003 on the first and seconed ring gaps, will also allow the rings to "grow" a tad without the end butting and flexing during hard runs, or a miss calculation in the tune that would give you a lean condition.

I just posted about the Supertech piston that you are thinking of.
https://www.miataturbo.net/engine-performance-56/first-look-supertech-pistons-1-8l-dohc-65235/
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Old 04-18-2012, 10:01 PM   #4
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welp, looks like the store I bought the pistons from said the supertechs are on a nationwide backorder from supertech until....... mid june. Anyone know of someone with them in stock?

Wait for them? Or try to find a comparable piston? I like the pricepoint of the supertechs, but not sure if I can wait that long
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Old 04-18-2012, 10:17 PM   #5
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A quick check of some net catalogs, shows 9:1 cr forged pistons made by both Cp and JE

I have no data to share, but I have both in diffrent builds over the years.

I have no Idea on price.
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Old 04-19-2012, 02:57 AM   #6
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After holding a JE piston in my hand from a Miata motor, go CP.
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Old 04-19-2012, 04:45 PM   #7
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looks like I'll be doing both options :P

getting some topline for the current engine so it's going to be the budget build with a hone first

got my extra engine sitting in the garage, so that will get the supertechs and forged rods once they come in stock.

just want to get this thing back on the road, way too many sunny days being missed :(
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Old 04-19-2012, 05:01 PM   #8
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Can I ask why topline? Not NPR?
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Old 04-19-2012, 05:12 PM   #9
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forgot if it was on miataturbo or somewhere else comparing the topline pistons to another brand and the quality was a bit better on the topline. most people that i've seen have been recommending topline for cast. other than that, not much of a reason?
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Old 04-19-2012, 05:28 PM   #10
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Ok, I can go with that.

Reason I asked is NPR is an OE supplier to some of the Japaneese car makers.
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Old 04-20-2012, 01:06 AM   #11
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hmmm, I'll keep that in mind next time I have to buy pistons learn something new everyday, thanks!
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Old 04-20-2012, 01:22 AM   #12
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i picked up some wiseco's after contemplating literally everything...
why?
cause they were new, but they were 2nd hand. i'm ok with that.
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Old 04-23-2012, 02:56 PM   #13
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Wow, I think I just picked the time that everyone else is doing engine rebuilding.

Topline pistons are out of stock.
Npr pistons on Ebay don't exist for a 1994.

I've had my orders for pistons canceled on me 3 times now lol

However the supertechs actually came into stock early and are shipping to me, but I've decided that's for the other engine now
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Old 04-23-2012, 05:03 PM   #14
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The supertechs came in early? When I spoke to ST they told me they were expecting 10 sets of the 8.6:1 cr pistions in 8 weeks.
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Old 04-23-2012, 05:16 PM   #15
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Well, I guess they had one or something. It's already on it's way to me technically. The place I ordered from said supertech told them it was backordered, got a refund, but during the lag in communication, they then said supertech had shipped out my order even though I was issued a refund. Then I paid again.

Funny thing is, the package, according to tracking, was already in my city, and supertech issued a package intercept as I had originally been refunded. Now the intercepted package has to go all the way back, and then shipped to me again.....

stupid communication problems
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Old 05-01-2012, 03:06 PM   #16
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awwwww yeah finally. took about 3 weeks, but I guess better than waiting until June. thanks guys for the info and help. funny thing is, everywhere I tried to order cast pistons for the other engine, they're all out of stock too... topline, npr, etc. :(



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Old 05-01-2012, 03:16 PM   #17
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Now scale them and see how close your box is.
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Old 05-01-2012, 03:19 PM   #18
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will do. got myself a digital scale still gotta balance my rods too, but I'm just happy they actually got here. I've been in limbo for almost 2 weeks waiting on these things
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Old 05-01-2012, 07:39 PM   #19
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pistons weigh in at 297, 297, 298, and 299 grams each. I need to get a smaller scale that measures in 10ths of a gram
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Old 05-01-2012, 07:41 PM   #20
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What are the wrist pin weights?
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