well lets see here....after 9+ hours of doing searches about top ends on here dating from 03 til just a couple days ago,and a 40 minute phone call with JoJo Keller,I've found that the "majority" of guys still choose Wiseco.I myself have yet to have any problems with them,been using them for 32 years.I even have an 81 KZ1000 with the Wiseco 1400cc big block kit that I installed in 98 and have 28k miles on it and it still rips just as strong as it did since I installed it.I recently re-rung my KX5 roughly 15 hours ago(Wiseco)and had no problems,compression was at 175 right after I installed them,now it's at 170....and that's on a jug with 4 seasons on it.Should get a hair more when I throw on the new jug.I'm not doing my rebuild til mid March or so,so I'll be watching this thread and any others closely.I see Motorrad,Alward,and a couple others are thinkin Wossner.I've never tried them,but if you guys like them,then I'm on board too.
As for OEM cast...ugh....I found 21 posts of pics of cracked/shattered cast pistons on here,and NOT ONE of forged.Not saying there is'nt any posts of forged pistons grenading,but after 9 hours of searching,I had had enough.
After talking with JoJo,he also swore by Wiseco and forged in general.He used Wiseco through-out his whole racing career...EXCEPT in 1984,he said he chose to run his YZ490 with the OEM cast at Southwick for practice...and on his final lap,his bike locked up...cast piston shattered.He said after that,he came up with the motto..."you'll come in last,if ya run cast".
Not that he was ever the king of motocross or engine building,but it's from someone with a ton of experience.Then there's several posts from Stewart,who replyed several times..."cast won't last"...and coming from someone that has dedicated EXTENSIVE hours of building and testing the KX5 motor as much as he has....I'll listen to him long before I listen to someone trying to suggest I run cast!!!...in any of my toys!
So for the guys that swear by OEM cast and have never had a problem with them....I say Good for you,and best of luck to ya.
ALL the proof that I or anyone else will need,is right on this site.
Foxx