What Pistons are These?
 

Picked up an engine the other day. Supposedly had new crank, Eagle rods, wiseco or Supertech pistons and never been driven, started and idled for about 5 minutes before running out of fuel. Back story is that the guy who built it was killed in motorcyc wreck and his brother was selling stuff off to help the family. Didn't know details but had photos of the build. The engine came out of a '94 and was built for a turbo. Pan is tapped for oil return. I pulled the head and here's what I see. Obviously new pistons but I don't know what they are. Slightly raised in the center and stamped "STD". I assume that is for standard bore not sexually transmitted disease. My Intention is to use this block and engine for a 250-ish whp build with VVT head and my FM2 kit.

Before I tear it down further does anyone recognize these pistons? Could they be Supertech? If I can identify them as NOT useful for me I'll put the engine back together and sell it. Cylinder walls do not look like they were honed, so if I'm going to build this motor I'd tear it down and have it looked over by a machinist.

what type of pistons are these?

Paul

Paging Dr. Ridethecliche, piston conneuseur.

Looks like they are cast instead of forged?

They look a lot like factory pistons.

Those do not look like Supertech pistons. Looking closely at the surface of the valve reliefs, they look cast. I think the Wiseco's have their trademark on the skirt- at least the photos I've seen. I can't recall if they have the forward mark or not.

The valve pockets aren't machined. The wiseco I have in my engine are machined. Pics of Supertech show machined pockets also. Hopefully, you didn't pay a premium.

EDIT: ^ as I was writing.

They are stock pistons.

Google stock Miata pistons and yours will come right up.

Looks like a stock 9.5:1 99-00 slug e: nm, not quite enough dome (or maybe they are dished, the pics aren't clear). Probably an 8.8 or 9.0 as you said.

They look dished to me, not domed.

From solomiata.com:

http://fixjunk.com/solomiata/solomia...toncompare.jpg

Have you pulled the oil pan to look at the rods? There are folks who do a "rods only" build with stock pistons, so it may have decent rods underneath.

--Ian

Pulled the pan on my Facebook found engine and was pleased to see that the rods are, indeed, forged. Appear to be Eagle rods but do not have a name on them. There is a number "1090" stamped on each half of the crankshaft boss.
Looks like I need to decide if I'll be satisfied with 9:1 stock pistons for my build or if I go for forged.

Paul

Depending on how much you're in it for, you might as well use it as is under the constraints you've discussed. If you want more, you can build another motor on the side while you enjoy this one. That way you can take the time to build it right if you want to make bigger power without worrying about your rods getting all bendy on you.

It's not a bad option given you already have this.

That said, if you don't think it was honed, you're going to have to pull everything apart, hone it, get new rings etc... at which point the cost of pistons isn't astronomical given that you're going to be taking the motor and having machine work done anyway. If the motor was 'good' as is... it might have been an easier decision you know? Buttttt if you're confident enough in your ability to do a dingle ball hone at home, then it would make sense to consider running things as is.

I think Pat wrote about this ages ago. He had essentially done 3 things over time:
1) No hone, but new rings. That motor burned oil.
2) Meh hone, new rings. Motor burned minimal oil.
3) Good hone, new rings. Obviously this worked well.
(I think I have that mostly correct).

So if you want to take your chances and give it a decent hone and new rings....

Found the thread!

https://www.miataturbo.net/engine-pe...5/#post1202874

AIUI, one of the advantages to a "rods only" build is that you basically just pop a piston out, swap the rod on it, and put it back in. Same piston, same bore, same rings, no additional parts or labor required, but you pick up some rod strength. If that's true (never done it myself), then is a the lack of honing actually a problem? Is there enough wear on the walls that it needs to be honed?

--Ian

Most "rods only" builds aren't that ghetto.

Some are. Most aren't.

Personally I'd slap the VVT head on it and go with it as is. The NA pistons + forged rods seems like a great setup for your goals.

Mine are. Both my ghetto builds worked out great.

That's the way pdexta did his current motor and it obviously works better with a lower miles setup.
Most tend to do a dingleball hone and use new rings, as well as use bearings from a rebuild kit. Theoretically the bearings should drop right in for the swap if they're standard sized oem replacement bearings and the crank isn't damaged. I've even read of a few folks on here that didn't even bother using plasti-gauge since the expectation was that things should line up if there was only normal wear.

Edit: Talk of the devil lol.

Yeah Boileralum and i did his motor the ultra ghetto version. But if you already have motor out of the car with the thoughts of tearing it down to check PO's work, literally no reason to go down that road. Absolutely none.

I appreciate all the input. This WILL be my motor built on the side. My original engine is still in the car and running fine. I have no need to rush this job. No idea why this guy put new rods, pistons and bearings in an engine and not even hone the cylinders. Think I'm going to ponder my options for a few days. $ aren't a huge issue and I have time. Just a little rusty. Haven't done internal work on an engine in almost 50 years. I think I want to do it right.

Paul