Cast(Pro-X & Stock) vs. Forged (Wiseco)Pistons

I was wondering the same thing awhile back, so I did a little research through old mag. articles and such. Although I'm sure there's a lot more to it than this, here's the basic info I came up with:

Cast - Typically will last longer than forged pieces, but weigh more. Also cast pistons typically have a greater piston to wall clearance because they are seceptable to heat expansion.

Forged - lighter weight which helps the motor build rev's faster, but tend not to last as long...requiring more frequent top-end rebuilds. Usually they will have a tighter (lower) wall clearance since aluminum doesn't expand as much as a cast equivelent.

Now I've used both forged and cast pistons in my rebuilds, and never noticed any real difference in engine performance (revving faster) or longevity. Granted, my riding is usually limited to maybe 2 evenings during the week and a full day on the weekends, don't race, and tend to run my premix a bit richer for added lubrication. I also always rebuild my top-end over the winter with a new piston and rings, but I've never had a scared or damaged piston.

More than likely I could run a cast piston for more than one season, but I like the added peace of mind of knowing I have a fresh top-end every year. Mostly I think it boils down to a matter of personal choice and preference, but I will say that I've seen more grenaded forged pistons than I have cast pieces. Just my $.02

TrailDawg,

I think you have it backwards, the forged pistons need more bore clearance to keep from sizing. The some times weigh more than the cast piston (unless you use the pro-lite type)

The wrist pin boss goes all the way to the head of the piston, because it is struck with a one piece die. This also causes a grain pattern and if it is machined away the piston will distort under heat. And this is why they need more clearance.

The cast piston uses a 3 to 5 piece inner die core allowing the pin boss to be under scored. and this makes the piston lighter. Also cast piston have little to no grain pattern and will not distort like a forged piston. And that why they can run a tighter clearance.

Hope this helps, I have been boring and using both types of pistons for over 30 years.

And that's my 2 cents worth.

A mite bit wrongwards, methinks.

It's forged that expands more, not less than cast. Think of a forged piece having a 'grain' (like wood) and a cast piece having no grain (like masonite or other 'wood-like' material). Real wood expands/contracts more than it's kinda-like wood counterparts.

That's why wiseco has had a bad reputation by some. They (the proverbial 'they' ;) ) rebuild their oem cast piston bike using a forged piston, but with the same clearances listed in their manual. The result?

Stickage.

Well, back in the days when you actually FIT such things. These days, with nicasil and chrome and all...that isn't much done.

Anyway, it's not wiseco's fault or problem.

The issue is more of 'rate of expansion'. This off a website regarding wiseco pistons. No, it's not related to kawi parts...but to forged pistons in general:

The slighly higher expansion rate of the forged pistons..

Click to expand...

.anyway, it makes the point; forged=more

A big plus to a Pro-X piston...they are available in the 'A-B-C-D' tolerance sizes whereas wisecos are not.

A kdx is marked, cylinder and head with one of those alpha marks. The difference is only 1/2 a thou... .0005, so it's not huge.

But...why put your bike together with .002"+ piston/cylinder clearance when you can snug it up a bit with the correct (cylinder being ok and all) size piston from Pro-X?

Oh...the 220 has a known piston design problem. So say people that should know, anyway (like CDave). The general idea is to use a wiseco if your 220 is modified to any extent.

Contrarywise, the 200 oem piston (same as from Pro-X) is good to go.

My $.02 as well.

.....consider the source!! ;)

***edit***
Well... I started my reply before he said the same thing. I may be a dayposter, but I'm slow!!

Thanks for the correction guys. Guess the old memory isn't what it used to be...kinda scary considering I'm only 28 :scream: God help me when I hit 50 and can't remember how to buckle my boots :(

So, all in all, if you're not reving the thing to death, and you don't want to/need to replate, wouldn't the smart engine builder choose the most correct "fit" over material type?

That would be my choice...but then, I'm close to 50!

...and I can still buckle my boots!!!
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(..if I can FIND the darn things..;) )

I'm 44 and just begining to think that some day I might have to wear glasses (or contacts).
I'm still pretty sure I'm not gonna die though; isn't it great to be healthy & in denial about the obvious?

i took a wiseco pro-lite witch wieghs 215grams and filed it down to 185 i noticed a big horse and torc gain.