Hi fellow KTM Guys,
Yes its true I commisioned J&E to make a small batch of 95mm pistons to bump the displacement of a 400 to 454 just by boring and NICOM plating the stock cylinder, or by using a 520 cylinder. The first machine is used for dirt track in District 16, rcaed by Joe Barr or Barr's Kawasaki KTM The head had to be matched with some minor adjustments to accomodate the larger piston's squishband and to set the compression ratio to 13.2:1
The second test bike is owned and raced by Dave Antolak of TUF Racing. On that bike head will be modified by raising the floor of the intake port to increase the short side radius. Because KTM uses so many common parts for the LC4 engine series, I think that the cylinder head's ports are way too big for the little 400 making the overall powerband a bit boring. Some could argue that its traditional European but lots of riders beg for the thrill of a YZF from the smaller LC4. We're going to run the squish clearance tight and set the compression ratio up near 14, then use Phillips B37 fuel.
Dave's bike is unique in that Ohlins has built him a set of forks and shock for his KTM400
Apparently Thumper has a 95mm piston kit for the KTM. Inquiring at Wiseco they reffered us to Thumper but when we called them nobody working the phones knew anything about the kit. Perhaps they didn't want to sell just a piston kit to us knowing that we'd handle the cylinder and head ourselves. We finally gave up on trying to buy a piston kit from them and opted for the J&E prototype batch. I figure that this model will be around for a lot of years and that for many riders, a 520 is just a bit more bike than they really need but a 454 with some head work and a choice of compression ratios would be just perfect.
I'll be ready to sell kits this winter. The kits will be in stages. You can buy a piston kit and 95mm head gasket $200, or the top end parts with overboring/NICOM plating/diamond honing, and instructions for modifying the head for $350, or a kit with complete porting and valve service with the big bore for $500
For you guys thinking of buying a 400 and spending another $1800 to make it a 540 consider this, Barr's Kawasaki/KTM has 2001 model 400s and 520s on sales for under $6,000 and Wiseco makes a 540cc kit that runs about $325 to bore and plate with the top end parts. Barr's will even sell you the new bike with the big bore kit installed for a modest labor charge. For anyone interested, Barr's is located in Madison Wisconsin and the telephone number is 1-608-222-6800