Second guessing my piston choice
 

I have been planning a full rebuild of my high mileage MSM for 6 months or so. My power goals are 200-250 (basically whatever I can make on my rebuilt stock turbo) I already have a larger intercooler, FM intake, Turbosmart MBC and recirc BOV, and a castles down pipe.

I bought some 0.040 84mm DNJ pistons that I blasted, ceramic coated and shot a dry film coat on at work. My thought was I won't go over 300hp so I should be fine. But now I am second guessing myself. I am thinking of dropping $500 on 9:1 Supertech pistons and doing the same coatings on them.

I have two questions: is it worth it for my power goals? And product pictures on the web are conflicting. Are the current Supertech pistons P4-MA84-CR9 shaped like OEM pistons, or are they a short skirt/short wrist pin design?


More info:
my head has been mildly ported, valves deshrouded and back cut. Chambers will be ceramic coated as well as the turbo manifold, turbine housing, and turbo elbow. I bought basic clevete bearings. Gaskets are feel-pro. Valve springs, guides, and oil pump gears (for stock 2001+ housing) are Mazda OEM. lightweight flywheel and stage 2 clutch. I have a set of forged rods, Bosch 330 EV14's, and MS3 will go in after the rebuild.

go for 8.6cr if on pump gas.
id def use the supertechs because you're doing all this work might as well do it once

That is what I am leaning towards, doing it once. As long as I can get 100k out of it. However I would rather have higher compression 9:1 or 9.5:1 for off boost response and overall efficiency. I can tune for the compression, and the MSM turbo is so tiny so I doubt I will go over 15psi. So I want to build it for low boost. Even eliminating the oil squirters with forged vs cast will be worth something. The last Miata engine I built years ago I went all out chasing everything I could, but it was a ITB N/A engine.

That said every dollar counts. I already have coated cast pistons. And the money on forged pistons could be put towards replacing the stock MSM suspension with 150k on it. Or wheels, or shiny new tools etc.

Also I have all the tools to yard out an engine and tear it down and assemble/mic already. So except for The cilinder boring and crank balancing, I can do everything else. Even made a cool valve guide driving tool at work the other day.

What's the point in replacing pistons then? Just re-ring the stockers, hone the walls and keep on truckin

120psi compression, massive blow by. I bought the car with a blown head gasket, and when I had the head off I found a nasty pit in cilinder 2 and 3. I rebuilt the stock turbo when the head was off. think the original owner let it sit for awhile with coolant in the cylinders before I picked it up. I drove it for 1000 miles after the headgasket, mostly chasing all the other problems I needed to fix. Now that I fixed everything else it is time for the motor itself.

Thanks 18PSI, I finally decided on 8.5:1 Wisecos. They were the same price as Supertech with wiseco rings on fab9's web site. I have had much more experience Wiseco pistons than Supertech , I am aware of the alloy differences but for the same price I think the Wisecos are better quality.

I did some more thinking and the safety outweighs any tiny benefit of 9:1. I will still ceramic coat the crowns and dry film the skirts as well as combustion chambers and valve faces. In the end this engine should be overbuilt for this car.

now I am debating with myself if I should go from the Clivete A series rod bearings I have to ACL. This is street motor, so normal bearings in the mains, but the rods ar the end point of the oiling system. So a harder bearing would be less of a concern, but would it even be of benefit on a street motor that sees fun runs and hand full of autocross runs a year?

I had wiseco pistons once, pieces of it went missing and destroyed my BP4W and my first EFR.

Been happily trucking along with Supertech for two years as a daily driver.

YMMV

You wouldn't by any chance be selling this Pistons on eBay? Just place a bid on some for a mild 1.8 built.

The wiisecos will be slick side coated from the factory, you just need to do the crowns.

Yes, get the race rod bearings, they will be able to take the increased loads a bit better

Considering cast pistons, bought Wisecos. That escalated quickly. Wisecos are just about the last piston I'd pick if I were building a street engine, and the only Wiseco I'd ever consider using would be the FM version.

Those were probably my pistons then. Should be great for a mild build. As time went on my desires for my build changed from stock turbo to something in the 300hp realm latter on down the road. And the longer I waited until I had time to build the engine the more my plans changed.

Brian from M&B cylinder heads set up my PTW clearances. He is well respected in the 2JZ world and I trust him. So far so good the engine is very quiet and smooth. Right now I am getting my new MSPNP Pro set up.

Sav could you educate me on why you don't like them for a street engine? It it because of the alloy or because I cant use oil squirters? That said the engine is already built and running so it is a moot point, but I have had good luck with Wisecos in the past on Toyotas and bikes, and a 1992 NA ITB build I did over a decade ago in college.

Personal preference. I see no reason to tolerate 2618 in a motor which will never use more than 30% of the capacity of that piston. I've encountered some extremely noisy Wisecos when cold, personally, although the FM version is supposed to be better. I like the STs for the alloy, 4032 allows for a much tighter PTW clearance and a much quieter motor. Wiseco motors tend to be a little clattery and noisy, especially when cold, but all the ST motors I've ever built have been OEM quiet, even from cold start. If I were building a 600whp drag BP with sleeves and billet caps, then yes, I'd go straight for a set of Wisecos, but for a 300whp street car, they're the wrong piston for the job IMO.

My FM wiseco's have been in service for a few years, and have done well. Silent on startup, no complaints other than $$$.

this guy right here, speaketh the truth.
+999

Fair enough. Thank you for your hard won knowledge. I can just be thankful that so far my engine is quiet when cold. At least my wisecos ended up being the same price as Supertechs, but I now know for next time.

I have the non-FM Wiseco and they are a bit noisy when cold. They also seem to clatter a bit when I'm driving warmed up, though I can't tell if its the pistons or the valve train which is typically loud in these cars. However, blackstone has shown the oil to be mostly clear of metals, with everything coming back in single digits by the last oil change (engine at around 8000mi). This includes some track days and some street driving making 330whp and 20psi

Next time around, I'll most likely get Supertechs, but I certainly haven't had an issue with my Wiseco as of now. I wasn't aware of any issues with them, but I built my car a few years ago, and the build took a few years, so I'm sure more parts have been torture tested and some of the stuff I have is "obsolete"....I mean I have a Boundary pump with no shims and I run a turbo AND oil cooler...no issues....YET lol

All that extra clearance required with 2618 piston takes its toll on skirt life during the warm up cycle. This is why they are a poor choice on street motors. The extra strength is of no benefit in most Miata applications. Now for a track car that spends most of its life 8k+ its perfect for the job. Warmup cycles happen much less frequent so piston skirt wear is not much of a consideration.

The 4032 is a high silicon low expansion piston. It's much stronger than stock and can be fitted with tight tolerances. These are best for the street and most track applications. Unless extream heat, rpm or hp it's really the best solution.

FWIW I run super techs in my 297whp track car. It lives between 6-8. No smoking, noise or any anonymities so far. Would make the same decision again next time around.

EW you'll be fine with the weisco pistons. Not the best for long life on the street but at least you don't live in the snow belt where temperature swings are more extream. In the north east I bet that would be a one or two season motor.

Damn!

It's a matter of personal preference.

I would never use anything but the Wisecos. I have seen far too many ST crack at the valve reliefs. My Wisceos have endured 5 seasons, that's roughly 20 hours of operation in competition and have never skipped a beat.

But my car isn't a 300hp street car. And it does sound like a diesel when it's warming up. I don't use the temp gauge to watch it warm up.......I use the vacuum gauge :)