21251 pistons..Can they be used or not?
Turbo Mini Forums

Hello. I'd like to know if anyone has successfully installed these 21251 pistons and what their experiences have been.

I know they're not the best pistons you can install, but after measuring the cylinders, I'm seeing that I'm just slightly outside the standard tolerances and I'm forced to go with the 0.020" oversize. I have the opportunity to get 21251 pistons at a very good price. I'll be using the car sporadically, on weekends, some spirited driving, but nothing like racing all the time. The engine has a 998A+ camshaft and I'll be revving it to 6000 rpm. I know that high revs are the main weakness of these pistons. It will have an intercooler and an IHI VL38 turbo like the one in the Abarth, which operates at around 10 psi. It's a very compact and efficient turbo, and I managed to install it with the Metro Turbo exhaust manifold without modifying the bulkhead. The idea is to get around 120/130 hp. Above all, I'd like to hear opinions and experiences from people who have them. What results have they obtained? Pistons with holes due to poor combustion, there will be cases of 21251 and omega forged pistons.

They are generally considered a bit fragile for boosted use. The 21253 is the better of the budget pistons and will handle some boost.

Phil.

WWW.TURBO-MINI.COM

When building my 1098 engine I was recommended on here the calver st pistons I’m running 12g 295 head larger valves T2 turbo that had a slightly bigger inducer wheel as the compressor housing had been butchered. Running on 11.5 psi at the moment made 105 bhp at the wheels at about 5500rpm if I remember right done around 800miles so far.

I'm noticing that the 21251 pistons, despite having a very large groove for the lubrication ring, have reinforcements extending from the center of the wrist pin that support the piston skirt, stiffening the area. It's not that the skirt is left hanging in the air with little support, as is often said. I suppose this design should keep things in place and significantly improve lubrication against the cylinder wall

Avoid any piston with a big open groove like that for boosted use.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Hi. Thank you so much for your replies. I've finally decided on the 21253 piston and will machine the crown and lip to lower the compression height and get around 11/12cc. The goal is to reach a compression ratio of about 9:1.

Now my question is about the piston-cylinder clearance. The piston head indicates a clearance of 0.03mm, which is about 0.0012". Personally, that seems like a very tight clearance, and I assume it's designed for a stock engine. I don't know if it will work well in a turbo engine. My intention was to increase it to at least 0.05mm or 0.002" to avoid seizing. What are your opinions on this? I know these pistons were widely used in turbo builds around here.