Help with Wiseco piston ??

[greencannon]

First time I've run into this. One on the left is 2yrs old and is being replaced by the one on the right, just got
it in the other day from my dealer. Whats up with this picture (sorry for phone pic quality) ??
Part numbers stamped on both pistons match 575M08600
the 5 digit # stamped above part number is different on each piston
1343I (used)    and      1485E (just purchased)on right
Both are identical except for the beautiful machining on the used piston
I'm assuming the machining is for weight reduction

[JustinSB]

Measure them to be sure, but I'd say your fine.

[ID KX500]

I am told that's a good thing. Wiesco is stronger.

[Motorrad]

That is a result of Stewart.  He got them to change their design.  The machined pieces opened up ports.. Mistake.  So new ones don't have machined bit

http://www.kxriders.com/forums/index.php/topic,5094.0.html
"wiseco leaving out the lighting cuts on the side off the pistons  is great for helping the stop the cross flow between ports but leaves an extra 30 grams in the piston..you can save 5 grams with the factory  kx wrist pin...or have the piston cut on the inside -Stewart"

[greencannon]

Can someone elaborate for me, as I am no detailed tech guru here.  ( helps stop cross flow between ports ) ?
the pic shows both wiseco pistons, the new one has no lighting hole on the exhaust side ( explanation ??)
 I do know it took me a few years to get my bike to run smoothly without pinging and bucking thru expirimenting with piston brands, port cleaning and advice from engine builders. It has been sucsessful for me and consistent with wiseco piston machined on the side. I will use "new style" piston because it's already paid for. But I'm really hoping it doesn't put me back to square one on engine performance....
 I don't like the idea of heavier, but like i said I'm no service tech.
Although I've tinkered with the cylinder over the years, it's basicaly still stock. Anybody with same situation run into this yet and how did it affect performance
THANX GUYS

[Friar-Tuck]

 It's O.K. GC,
  Motorrad is not the kind of guy to steer you in the wrong direction.  It is the replacement for the old design.
Here's the link to the discussion: http://www.kxriders.com/forums/index.php/topic,4409.0.html

You can offset some of the additional weight by cutting a window in the piston, this gets you almost 300 some odd degrees of intake. (If the engine can draw any more from the reeds)
 
  Tuck\o/ 

[greencannon]

Ok, I get the jist of the new design, but dont understand why the window cut is not part of the new design.
 If you take a step foward with new design, why would you take a step back by keeping it heavier seems everybody is modifying the new design out of the box....
I dont plan to cut window on new one. I don't have the means. I still dont see if anyone has run one without cutting the window and what results were.
Thanx again guys