TA-Wizard

Just got a set of forged Speed-Pro 2256F skirt coated pistons. Instructions say to run them with .001 minimum clearance?????

I have been using Wiseco and JE/SRP for a few years, and have gotten used to .004-.005 clearance on forged pistons.

Does anyone run these pistons this tight??? What alloy is Speed-Pro using that does not expand as much as the others???

RB83L69

It's the coating that makes the difference... just follow the instructions, all will be well

TA-Wizard

RB,

Do you use these pistons?? I checked the Speed-Pro website and the non-coated 2256 pistons also run a .001 min bore clearance.

What gives???? I am all for them using an advanced alloy, but, when every other forged piston I have used for the past 10 years is running at .004 minimum, it just makes me a little nervous.

I will be laying around a 200hp shot of juice on this motor and I don't want any problems.........

Damon

I've used them. They'll be fine at .001. I do them about .0015 becuase I'm the nervous type, but like RB says- all will be well.

Forged pistons expand quite a bit more than cast or hypers. That's the main difference.

TA-Wizard

thats my question.....these ARE forged pistons.....so they will (should) expand more than cast or hypers. I have used various cast/hyper pistons fitted very tight (.001-.0025) with good success, but, forged are always at least twice the clearance of cast/hypers.

How in the world they can fit forged pistons to .001 is a sign that we are in the 21'st century I guess.

tom3

Think these have a special alloy, some silica or something in them. Even years ago the TRW forgings of the same number were spec'd at .0015, but I honed the cylinders to .003 anyway, they ran great at that. The coating may wear away pretty quick to give that little extra clearance.

ME Leigh

Yep, those Speedpro pistons are essentiall forged hypereutectic
pistons. Meaning they have large amounts of silicon in them.