Piston question

[Hellfrekke80]

There are two types of KB Hyper pistons: one with a D quench pad and one dished all the way around; these 944s have a D quench pad. I'm curious if anyone has encountered any issues, or if there would be any issues transitioning from forged to hyper pistons in terms of cylinder wall clearance.

[Russ Pottenger]

The short answer to your question is typically a Forged Piston has a bigger growth rate than a cast or hypereutectic piston and therefore requires more piston to cylinder wall clearance at room temperature to compensate for the growth rate.

The important part, and I think the basis of your question is that the clearance difference is built into the size or dimension of the piston. Meaning a .030/3.905 finished size 4 should have the proper clearance for either choice of piston. Cast/Hypereutectic or forged.

Hope that made sense. : )

[RoadVanguard]

So I just realized that KB makes a Hypereutectic piston for the Jeep stroker that you can use with the 4.0 rods that are much cheaper than the IC944s forged pistons...I imagine it's because of the materials used. I've bought one 944 piston in order to replace the damaged one, and there's been some upgrades compared to the original 944s, like they now have coated skirts and are about 18g lighter cause they have less material on some areas, so I've been thinking of replacing them all.

The other 5 pistons look ok, but there is some wear, like some vertical scratches that were most likely caused by having water in the oil from the cracked head, and they all show the same identical wear pattern but it didn't look too worrisome; but nothing beats new pistons.

UEM will sell me the rest of the 5 pistons in a way so that it'll be like I bought a set of six 944s, but even then a set of the Hypereutectic pistons still comes out cheaper.

So my question is, how much of a risk will it be if I put in a set of the Hypereutectic pistons since I had the forged 944s in the engine first? UEM said that I could make up some clearance with the Line2Line coating, but I'd have to tell them how much to add and I don't know what to tell them.

Is it too big of a risk to put in a set of Hypereutectic pistons after running forged pistons? How much Line2Line coating should I ask to be added if it's even necessary?

Switching from forged pistons (like the IC944s) to hypereutectic pistons does come with some considerations. Forged pistons, like the IC944s you currently have, are designed for higher performance and can handle more stress, heat, and detonation compared to hypereutectic pistons due to their stronger, more ductile nature. Hypereutectic pistons are less expensive because they are cast with a high silicon content, which makes them harder and more wear-resistant but also more brittle and less tolerant of detonation.