Piston details

[cdn280]

Ok, I've searched, but more info is just leading to more questions.
My stock 300cc domed piston is marked W. A couple previously have said that this means Wiseco. Well Wiseco rings were too thick. (GG distributor part # marked Wiseco on the package) So maybe W means Wossner ??? I got some Vertex rings from the dealer and they were the correct size for what I have.
Well I've been waiting for ever for a couple suppliers to get me a coated Vertex piston kit, to no avail. So I'm looking at the coated Wossner pistons now, but every place I find shows it as a flat top piston.
So my main question is... can anyone report the differences going from a domed piston to a flat one ? (or vise-versa, 250 or 300, I've got a 250 cyl as well)
There must be some big compression and combustion differences. I did see that someone said that flat top tends to make more top end power.
And, any comments from people who have used both cast and forged pistons in the same engine ?

[Todd5774]

Can't help much than to say Ive found it trickier to jet my 300 when I went from a flat top piston to a domed one, I've started experimenting with base gaskets now as I wasn't happy with my jetting despite trying all sorts of combinations of needles and different mains and pilots. It's been 6 weeks since I replaced the piston and I'm still looking for that sweet setup.

Have even contemplated getting another flat top piston, and going back to my original settings.

[cdn280]

Originally Posted by Todd5774

Can't help much than to say Ive found it trickier to jet my 300 when I went from a flat top piston to a domed one, I've started experimenting with base gaskets now as I wasn't happy with my jetting despite trying all sorts of combinations of needles and different mains and pilots. It's been 6 weeks since I replaced the piston and I'm still looking for that sweet setup.
Have even contemplated getting another flat top piston, and going back to my original settings.

Which domed piston, and which flat one ? I just went thru a bunch of experimenting this yr to finally get my 300 finally working right with a Knarly pipe. What problems are you trying to sort out?

[GMP]

Domed to flat and visa-versa will radically change squish and compression. I can't see just doing a swap without having the head modified to suit.

All 250 pistons are domed, and the same as a TM racing 250 piston FWIW. I have always used Vertex cast pistons as replacements with excellent results, but it seems sources are few now. Wossner and Athena (forged) are more easily available. All are fine for use up to 100 hrs IMO.

[Todd5774]

Originally Posted by cdn280

Which domed piston, and which flat one ? I just went thru a bunch of experimenting this yr to finally get my 300 finally working right with a Knarly pipe. What problems are you trying to sort out?

The power is now all in the top of the rev range, and if I change a needle to get better grunt off the bottom it won't rev out on top, and then there are all the bits in between, a jd blue, 180m 40 pilot, as 2 will give me acceptable performance but not great plus it's hard to start..

Was using a wiseco piston I think, now I'm on a s3 which I think is made by vertex? Going to look round for another wiseco.

[bchatt]

www.s3parts.com

S3 are parts manufactures in Spain. they work closely with GG and produce parts for the Nambo bikes - head inserts, pistons etc. My 250 had a S3 piston stock, for some reason. It was a very nice piston and still looked great at 120 hrs. I replaced with a vertex and that has been fine.
Maybe you could add some base gaskets to bring peak power down the rev range a bit.

[TNT Cycle]

S3 was stock in 2010. S3 also made the cylinders for Gas Gas as well. In the states you can get S3 pistons...