Hi there,
I'm Hans from Munich (so please pardon my english
) and join the forum to get some info for my GN400-classic-racer project. Of course I let take part everyone here to (nearly..) all of my knowledge..
I do some hobby-racing with a
slightly modified XT500 with the
Grab the Flag, where "no japanese four-valves" are allowed. The GN is for my brother in law, who won't ever sit on a Yamaha...
First I try to build up a reliable engine with 400ccm, and later perhaps will downbore it to 350ccm, or upstroke/-bore it a bit, to be competitive in the 500-class.
I found out, the GN-engine is very nice made, many things are solved much more elegant than in the yamaha XT/SR500 engines. Advantages for racing are the close gear ratios and the lower weigth.
Also the valve-gear seems to be less sensible. I ordered stage2 megacycle cam, and after having calculated the valve spring force, I will choose the right ones from
Schrick, as I made good experiences with his products, unlike with R&D-springs.
For the first trials I will use a Mikuni TM36(I've got a spare one) and later an old 38mm Mik. flat slide out of a DR600. Exhaust will be a megaphone with reverse cone (mostly no noise limit).
Info: XT/SR500-Pistons have a 2,5mm lower compression heigth, equal pin diameter, but exhaust valve pocket is not in symmetry axis and must be reworked. There are many aftermarket pistons with different compression ratios from woessner(athena), wiseco, J.E. and others.
I don't know much about the british racing scene, except what I read on the
http://www.bmzrc.org.uk/Cheers,
Hans