piston troubles

[XCredrider]

I just talked to Lorean Duncan about a cylinder he ported and polished. He said that i should not use a wiseco piston in it because it will be one headache after another. Why is that? I have never had a problem with one and the guy I bought the cylinder from was a good engine builder too and he always used wiseco and said he never had a problem. It used to be a pro desert racers cylinder. I forget who, ill have to ask again, but he said he never had a problem. Why would it be any worse than a pro-x like he recommended?

[zedicus00]

some peeple dont know how to properly break in a forged piston.

if done wrong a wiesco can cause headaches.

[wilkin250r]

Wiesco pistons are forged aluminum, Pro-X are cast aluminum.

Whoop-de-doo, so what does that mean?

Contrary to popular beleive, aluminum isn't actually one solid mass, with all molecules perfectly interconnected. It's made up of particles, almost like small beads glued together, called the grain structure.

When aluminum is forged, pressure is applied as it cools, and it is pounded into shape. This spreads out the individual grains in the direction across the dome, creating many flat layers almost like fiber reinforcing for fiberglass. It makes for a very strong piston, which is good. However, it also increases thermal expansion outwards against the cylinder walls, which is a bad thing.

With cast aluminum, all the little particles are round, so they expand the same in all directions.

Ok, so now we know the difference, what does it mean?

Forged pistons expand faster due to heat. This increases the likelihood of siezures, and makes jetting more critical. It requires a larger piston/bore clearance.

Cast pistons can be set up with much tighter tolerance, and aren't quite as picky with jetting and overheating.

[wilkin250r]

Me, personally, I prefer cast like Pro-X. True, Wiseco pistons are stronger because they are forged, but they also present a greater risk of siezures.

That certainly doesn't mean Wiseco is BAD, but my cylinders will typically go through six or seven pistons before they need to be bored the next size up. My first priority is bore life, not piston life. I hate wasting overbores.

[jon370r]

wilkin250r,
Where do you get the Niks pistons for your 340 big bore? I was under the impression they didn't make them for the larger bore sizes.

[wilkin250r]

Originally posted by jon370r
wilkin250r,
Where do you get the Niks pistons for your 340 big bore? I was under the impression they didn't make them for the larger bore sizes.

Directly from Duncan Racing.

No offense or anything, but next time you have a question like this, use a private message to avoid clutter in the thread. It's fine in the Open Forum, but in the technical sections we like to keep threads clean and informative.