Im going through with this as we speak. I think its a tough call on using pistons that weren't originally in that bore from the factory. But i think jafromobile did it with his kia 4g63 build. And imo if he did it, its acceptable. That dude is crazy.

https://cimg5.ibsrv.net/gimg/www.mia...5ffca178d6.jpg

my "rods only" engine.

AIUI, if all you change is rings and everything is in good shape, then a simple hone is fine. if you change out any piston and don't rebore, then you're playing with fire.

--ian

Thanks! That's what I figured.

The difference in compression between the NA8 and NB1 seems to only be ~.5 so going through all that hassle doesn't seem to be worth it. I.e. if you're going to rebore...might as well just get the pistons that would make the most use of it.

Another bigger issue is using "used" pistons to get the lower 1/2 point vs buying new OEM. And, if you buy new OEM pistons you're within a couple hundred of forged anyway. But the forged force the bore + hone vs just hone.

Personally, I'd never go with used OEM pistons in an engine I was putting money into.

Hi OP! Heh.

What all did you end up doing finally?

I have a build thread that needs its title changed.

-Cleaned stock pistons/rings very well
-opened up top ring end gaps to .016"
-Manley rods w arp rod bolts
-acl main, rod, trust bearings. (All plastiguaged within factory specs)
-arp main studs
-arp head studs
-BE stage 2 oil pump
-ATI super damper

re-doing all fuel system components
-dw300
-fuelab inline filter
-fm fuel rail
-ID1000s
-fuelab mini fpr
-gm flex fuel sensor
-all -6an vibrant braided nylon hose

-gen2 gtx3071 w/ tial .82 housing

Nice!

Did you have a machine shop do any of the work?

Yeah, I probablyyyyyy wouldn't be looking at used ones. Looks like oem is about 250-300 for pistons, aftermarket is like 100-150, but I'm not sure have been vetted here like the rods have been since folks don't usually half ass things if they're going through the trouble of swapping over the pistons.

You will want to hone the block. I think I paid a local machine shop $150-200 to cleab the bottom end, check specs, and hone.

This was for your rods only build right?

If the used piston don't have a bunch of scuffing on the sides, use them, the diff between OEM pistons as manufactured isn't enough to matter. Just hone the block so the new rings well seat. You should check the bores for taper.

Referring to the pistons that are mated to the engine already or other used ones if one were to try to switch compression ratios?

No problem interchanging the used pistons as long as they are in good shape.

Pistons don't mate or wear into an engine. I would want to measure the new and old to make sure they are the same within a few ten-thousandths. If they are, swap away.

Rover has been running a rods-only BP05 longblock for ~8mos now with good results. Reused OEM pistons, OEM rings, Manley rods, ACL bearings, ARP mains, and an OE VVT oil pump. No plans to run past 250whp on gas and 300whp on E85, so stock pistons were fine.

I'm nowhere near close to doing this, but I was just reading a billion different things that people had done so I figured this thread was a great place to keep the information going since it already had a tone of great stuff.

That's awesome info though. My goals are modest, but I want things to be reliable. Seems like rods (manley/ebay) with a few other supporting things like you outlined and potentially NA8 pistons will be pretty solid for a daily pump 93 bewsted setup. I think I'll be more than content with the 2560 setup with the 2.5 exhaust that I have waiting to go in. I just want to be able to enjoy it at a level that the setup can offer safely without worrying about a rod deciding that it wants a rumspringa.

Thanks a bunch for the info Andrew.

I read a few ancient threads on here about 8.8 NA8 pistons. Do those actually exist or is it just part of fabled miata kitty and unicorn lore?

They were around in the earlier engines and you used to be able to buy them but for now just 9.0's are available new in OEM pistons I think. 2 tenths ain't go to make alot of diff.

I was thinking of picking up used pistons and having them cleaned up. So figured I might keep an eye out for them.

If I had to buy new oem pistons, I'd likely just go forged (which likely wouldn't happen). I'd be reticent to buy no-name oem style pistons because I haven't seen them described, tried, or written about here. I was going by what you guys had said about just dropping in cleaned up pistons. I think the drop from 9.5 to 9 is worth it for pump gas, no? If the .2 doesn't matter thennn what's the point of .5 haha.

Lower comp helps on pump gas. If you had E85 I would run the highest comp oem piston you can get your hands on though. I have run 10.5:1 on pump gas and 20 PSI boost, it can be done with conservative timing. Low AITs are really important for that combo to work though and not knock.

.5 well allow you to run more timing. If you are needing pistons because yours are bad every little bit helps. To be honest with a 2560 turbo I wouldn't worry about running the 9.5's. I ran the FMII kit for several years with 9.5's. If you keep it around 12 psi max you well have no issues. The draw back to running stock pistons is the ring glands well wear out faster then with forged. The 2560 max efficiency is about 14 psi but running that much with stock pistons well probably wear stock piston ring glands out in 2 years, to where if you keep it around 12 they well probably last 4 years of doing track days, mine did.. So a .5 difference is not as important as say running a built high horse big psi motor.

Pat mx5 Doing 1/8 mile drag racing is alot diff then running on a track for 20 to 30 mins.