hammerhead251

Member
Feb 23, 2004
10
0
Major props to Eric and Rich for a great job and good advice.

This is the bike to replace the 525.

99mm piston, 11:1
Stroker crank (78mm)
EXC counterbalancer
1mm oversized Kibblewhite valves
Headwork by Forward Motion
Stock carb bored to 43mm
Stock jetting, no BK Mod
Hotcams 525 cam
Drilled airbox cover
Stock pipe w/can shortened 2.5 inches (due to race damage)
14/48 gearing

Comes out to 600cc even. KTM should sell it.

Thumper Racing did the cylinder, aluminum sleeve welded and machined in stock 520 cylinder, then chromed. I wanted the compression low to help top end (God knows, it doesn't need any more bottom). With this piston/cylinder kit, there is no case boring needed. Sweeeet!

I put it all together and it started third kick (I swear). Now it starts 1st or 2nd kick every time, and the bike isn't any harder to kick than the 525.

This is the smoothest, fastest bike ever. I've only timed three laps so far on my practice track, and one was even with my best lap ever, the other two were 1 and 1.5 seconds FASTER!

With this gearing, I am running 3rd and 4th everywhere. This bike pulls the same gear in the same corners as my 450 which has 13/48. 2nd gear is pretty scary with this bike. If I ever need more speed, 15 front and/or 45 rear should be no problem.

The most amazing thing to me is the throttle response. I expected the worst, but this bike is actually better than my 450 and 525 in rhythm/technical sections. I guess the 99mm bore pushes that big crank around pretty efficiently and 600cc draws plenty of velocity through the giant carb. Blip the throttle and she jumps!

I'm taking 'er to Birch Creek this weekend for the Ultra/Mega/US Eastern/whatever else series race. We'll see how she races. I also plan to have dynos done with different pipes and against my stock 525, my 470SX, and a stock 450SX.

Stay tuned.
 

Rich Rohrich

Moderator / BioHazard
LIFETIME SPONSOR
Jul 27, 1999
22,839
16,904
Chicago
I want to see some pictures, preferably as you are leaving darkies at the apex of a corner :)
 

hammerhead251

Member
Feb 23, 2004
10
0
Better yet, Rich, come and RIDE IT! You guys are supposed to be headed this way soon.

Tell Eric the 450 cylinder worked perfectly. Thanks a bunch!
 

theturbojosh

Member
Apr 13, 2004
48
0
600cc motorcross bike!!!! Do you win races by jumping to one end of the track and back? when your on the gate do you start out in fourth gear? can you even use the lower gears? please tell me I must know!!!! I am terrified yet foaming at the mouth over the prospect of that much displacement wrapped into a bike that is only a couple of bowling balls heavier than mine you should write a post on the power delivery, handling and ect......
 

Eric Gorr

Engine Builder
Jun 29, 1999
384
12
I know a perfect track for that bike. Hawkstone Park in England. The biggest dam uphill you ever saw on a motorcycle track!
 
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