GP, Pro-lite, or Flat top for a 134cc YZ125

[tyler_43]

Hey I recently had a post on here about my compression and I've asked my local mechanic and he feels it should be fine until April (which is when our Island Motocross series starts). Since our max. displacement in MX2 has been upped to 125-153cc (two strokes) I figured I might as well get it bored out seeing how it has the stock cylinder plating and probably needs done anyways. But as always, there's too many choices :whoa:. I've heard the Wiseco GP is a good durable piston... but will the lack of an intake window hurt my top end? The Wiseco Pro-lite I've heard is good but I'd like something that would last longer than an OEM piston. As for the Wiseco flat top... lol I don't even know what the benefit with that is :think:

 

[BigRedAF]

Put the piston in and trace the intake side with a fine point marker. Drill a hole in the window area and finish it with a dremmel. I used to do this with YZ's all the time, your piston wont break.

The window allows more fuel mixture to stuff the crank for the intake stroke. It helps the entire RPM range.

 

[tyler_43]

yeah the pro-lite has the intake window... I've heard they're good all around piston so I'll probably go with that. I don't think I'll go with the flat top either as head mods would probably need done... ?

 

[tyler_43]

hmm... so if I do take the dremmel to a Wiseco GP piston I'm assuming you trace the intake port at TDC?

 

[hot125mod]

the prolite has a .090 dome and can retard the timing cahnges on the ported cylinder eric recomends a flat top for that. the GP has a moly coated skirt and a ti nitride or some type of thermo coat for the top. I want to try one of those in my next bike. is the angle of the squish supposed to be two degrees greater than that of the piston.

 

[SBC383STROKER]

What piston do i use?

You already have a good start by using a Wiseco piston which are FORGED, therefore can handle more detonation, higher revs, more abuse and are much more stronger than an OEM piston wich are cast iron, very brittle. Now for the piston, any flat top piston with the right "quench", which would be .040", will be ten times more efficient than any other type of piston including a dome becausethe "flame travel" will never be interrupted by nothing unlike a dome. All pistons are equal in the strenght department, but for your application i would use the Pro-Lite. The reason why i wouldn't use the Flat Top piston is because you have to extensively machine the head to get everything right and without the proper knowledge and tools you would be hurting yourself and your motor.

 

[tyler_43]

well i'm going to get the bike bored and ported. The porting will take the timing into consideration for a flat top or a domed piston... however I don't really feel like the benefits of a flat top are worth the hassle of getting the head machined.
PS - OEM pistons are cast ALUMINUM vs. forged aluminum for the wiseco

my 1934 McCormick Deering antique tractor uses cast IRON pistons lol

so... it's still down to the GP and the Pro lite, leaning towards GP