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-   -   So I may need a bottom-end rebuild... (https://www.miataturbo.net/engine-performance-56/so-i-may-need-bottom-end-rebuild-92025/)

dleavitt 01-31-2017 10:57 AM

So I may need a bottom-end rebuild...
 
Long story short, my shortblock may need a refresh. New rings and a hone at the very least, but here is the thing: I only want to do things once. The pertinent details:

Current parts: Car is a 95, and has 151k miles. No track time, but some autocross with trips to the rev limiter over the last 10k. Before current issues showed themselves I had installed a SPM damper, oil cooler, coolant reroute, and a 6-speed transmission.

Plan/goals: Engine will stay N/A for at least the next two years, possibly more. Partially due to finances, mostly to allow me to learn to drive on the track safely. If I do go FI, I'm still undecided between Turbo or Rotrex, but leaning Turbo. Power will not exceed the reliable limits of the 6-speed on sticky street tires, which I understand is around 300whp for a turbo car. Car is a weekend/autox/track toy, and not a daily driver.

Like I said, I only want to do this once. My question is regarding the pistons: how long do the OEM pistons last? At 151k, I’m tempted to replace them either with new stockers or go with forged. I’ve read several threads about a rods-only build, but most of them seem to have less than 80k miles. I also know that the 300hp mark is close to the limit of the stock pistons.

thirdgen 01-31-2017 11:27 AM

You're in luck! I have a freshly honed/ re-ringed short block that I'd be willing to ship. It's a 2000 block, so it has 9.5:1 pistons in it.

aidandj 01-31-2017 01:41 PM

Don't replace pistons because they are "old", thats pointless. You are honing and reringing anyways. Replace pistons because you either want more compression or more strength. NB2 pistons will give you more compression, forged will give you more strength.

dleavitt 01-31-2017 01:49 PM


Originally Posted by aidandj (Post 1389805)
Don't replace pistons because they are "old", thats pointless. You are honing and reringing anyways. Replace pistons because you either want more compression or more strength. NB2 pistons will give you more compression, forged will give you more strength.

So barring detonation or other damage, the pistons have effectively no end to their useful life? Or at a mileage significantly higher than I'm at currently?

The car won't be driven a lot, but the miles it will have are going to be harder than normal.

Savington 02-01-2017 01:09 PM

I would look at condition over mileage. If the piston looks good with no FOD on top and no scuffing on the skirts, then I would have no problem reusing them to build a cheap rods-only motor.

dleavitt 02-01-2017 01:26 PM


Originally Posted by Savington (Post 1390047)
I would look at condition over mileage. If the piston looks good with no FOD on top and no scuffing on the skirts, then I would have no problem reusing them to build a cheap rods-only motor.

Thanks for the input! Shortblock is still currently assembled, but the tops of the pistons look good. Depending on the costs I get quoted here locally I may be reaching out to you.

shuiend 02-01-2017 01:49 PM

I am in the middle of a rods only build. 94 block with stock pistons, used m-tuned rods from a previous build. Machine shop charged me less then $150 for cleaning, honing, and making sure everything was good.

StanTheMan 02-02-2017 11:12 PM

you are rebuilding a medium mileage engine because you want to or that its tired?


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