Travis also machines and balances the crank 1400 grams lighter than stock, and the whole rotating assembly is balanced to the new parts to achieve a quick-revving smooth engine, producing more torque than you can wrap your head around. This reduces piston acceleration speeds and cylinder side loads on the upstroke, increasing reliability and durability of the engine quite a bit. ![]() The reason for the offset wrist pin is to allow the use of a stock-length connecting rod with the stroker kit. The 600 we tested uses a custom-machined, ceramic-coated CP 12.5:1, 99mm piston that has an offset wrist pin that works only with Thumper’s stroker kit. The stroker crank can be optioned with the 540 or 570 kit, producing 576cc and 600cc, respectively. Huge power gains over stock are achieved, then comes the stroker crank. From there, you can go even bigger with a 570cc conversion ($725) kit that Travis says is like adding nitrous to a 426 Hemi V8. We have tested this conversion kit in a Polaris Outlaw 450 frame with one of Thumper’s custom cam grinds and found it to be a very potent engine it will blow the doors off many built 450s with ease. Thumper’s KTM kits are extensive, and their enlargement options start off with a 540cc conversion kit for the 450 or 525 (actually a 510) engine that will set you back $525. Give them a call at (661) 424-1800 for more information, or visit FINDING THE EXTRA 90cc Thumper offers plenty of affordable power options for KTM-powered ATVs and motorcycles, as well as J-models, Can-Ams, Polaris ATVs and more. When we got the chance, we couldn’t pass it up. We have ridden plenty of Thumper-built machines before (and not one of them has malfunctioned), but we have always wanted to try the famed 600cc KTM. Thumper has all their own milling equipment and plenty of testing ground to put in the R&D time to make fast motors, and it shows. Then what? If you have a KTM, you call Thumper Racing.īased out of Santa Clarita, California, Thumper Racing is a family owned and operated business, consisting of Dad (Travis), Mom (Francis) and sons (Jake and Garrett). But what happens if you get bored? Surely some power-hungry ATV riders out there will grow tired of having only 45–50 horsepower. In the dunes, it’s a blast the huge torque curve makes wheelies and huge roosts just a blip of the thumb throttle away. In stock form, the 525XC is an open-class fighter-tons of power, comfortable Ohlins suspension, a lightweight chromoly frame and a whole lot of attitude make it one serious performer. The single-overhead-cam, four-valve RFS (Racing Four-Stroke) engine spent a good amount of time in KTM’s off-road motorcycles, achieving a level of refinement and performance we came to value when testing the biggest Katoom. Stock, it will outrun just about any other sport quad on the market today, save for KTM’s own 505SX. Minimal wear - less cylinder and ring wear, longer bearing life.No rider who has ever thrown a leg over KTM’s 525XC can call it slow-and if they have, they might need to take some time off for a mental rebuild.For all four-stroke engines with wet or conventional clutches.For use in all scooters and four-stroke motorbikes whose oils meet API SG/SH/SJ/SL/SM/SN standards.The oil is suitable for air-cooled and liquid-cooled four-stroke engines The performance of Bel-Ray Thumper Racing Synthetic Ester 4T oil far exceeds API SN and JASO MA2 standards. The oil provides maximum wear protection for valves, rings, cylinders and pistons. ![]() Developed for single-cylinder four-stroke and multi-valve racing engines. Bel-Ray Thumper Racing Ester Blend 4T is a synthetic (semi-synthetic) engine oil combining synthetic esters and mineral base oils of the highest quality.
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