2009 Yamaha JSR YFZ450R and 2007 Raptor 700

When it comes to top motor builders, companies on the West Coast like CT, Trinity, Sparks and Duncan come to mind. Back East, Baldwin, Rage and TC have the bulk of the business. If you live and ride in the heartland of this great nation, John Stallworth Performance dominates the game. JSR Performance has been building sand drag, motocross and Pikes Peak hill climb race engines for over a decade out of their Witchita, Kansas, location. While getting huge horsepower numbers to compete at the high altitudes of Pikes Peak may be the company’s passion, building machines for the average dune rider is the bread and butter for JSR Performance. We recently traveled to the Little Sahara sand dunes in nearby Wyanoka, Oklahoma, to try out two of Stallworth’s products. One was a 2009 Yamaha YFZ450R, and the other was a 2007 Raptor 700.

JSR Performance not only builds engines, they also manufacture cylinders, pipes and other high-performance parts for all major brands of ATVs and side-by-sides. They can sit down with you at their shop or over the phone and discuss what your motor needs are and build you a custom package, not just sell you an off-the-shelf kit.

The YFZ450 got the most attention out of the two machines in this build. Not that it needs it—JSR just likes to see what they can get out of a new machine like this. The Raptor has been out for a while, and JSR has figured out exactly what it needs and what it doesn’t.

To get a reliable 50 horsepower out of the 450, JSR took the head and gave it a complete port and flow job for $475. The intake and exhaust side of the head were smoothed and matched to the flow of the 1mm over Xceldyne valves for $825. Ferra, lightweight, $220 valve springs were used, along with Web Cams’s adjustable gear cams for $690. Even after grinding, the cams can be fine-tuned for optimum performance by how you install the timing gears on the cam.

JSR pipes have a lifetime warranty against defects, and they are one of the few shops in the country that designs and manufactures cylinders and pipes in-house, so they can truly build one-off motors that no one else can.

Under the head, a 13:1 Wiseco piston at $225 was installed. Wiseco also supplied their complete clutch kit for the project. For $805, the kit includes the basket, friction plates, steel plates, springs, inner hub and pressure plate. After the bottom end and top end were reassembled, JSR installed a $165 Fuel Customs intake and one of their own full exhaust systems. JSR’s made in America, $595 exhaust systems can be ordered with an oxygen sensor receiver welded on to the headpipe, so it can be used with the Power Commander 5, which has a wide band O2 sensor. This feature allows the tuner to monitor and set the proper air-fuel ratio, then lets the Power Commander do the rest. An auto tune controller adds $220 to the price of the $350 Power Commander. A set of CV4 radiator hoses capped off the engine upgrades on the machine.

John Stallworth has won Pikes Peak five times, and his motors have won seven times. A pretty impressive résumé from a guy who rides what he sells. Not too many motor builders race at this level today.

The YFZ450R chassis was left alone, although JSR Performance did install a set of ITP Dunestar tires mounted on lightweight Hyper Tech carbon fiber wheels. A pair of Trail Tech, SC4, HID lights were also mounted on the YFZ450R at $400.

The list of add-ons for the Raptor was similar to the YFZ450R. Up top, the Raptor received a custom ground Web Cam cam for improved mid- to top-end power. Kibblewhite valve springs at $178 replaced the stockers. Under the head, a complete 12:1 Wiseco piston kit replaced the stocker. The cool thing about the $305 Wiseco piston kit is that they include a top-end gasket set.

This machine was also equipped with a JSR exhaust system at $625. A Power Commander 3 is all that was needed for fuel manipulation. A K&N intake and filter ($165) were needed to finish the Raptor’s hop-up list.

A complete Wiseco clutch kit including basket, plates, spring and inner hub helped get the power to ground. Even after repeated drag races, the clutch never heated up or slipped. The wire coming out of the head pipe is the oxygen sensor.

The hard part about this test was trying to figure out which one of these JSR-built Yamahas we liked best. We rode the two machines all day and into the night, exploring the entire Little Sahara sand dunes. It was just as hard to see which machine was faster. Just like in stock trim, they are pretty equal. In our drag race tests, the YFZ450R always got the jump but never pulled very far ahead. In fact, the only machine in the dunes that could beat either of these machines was a fuel-injected Banshee, also built by JSR Performance. We will feature that ride in another issue.

The Yamaha motors both ran ultra-smoothly and always had power to spare. In fact, you could keep an even half-throttle up most of the steep climbs and only have to twist the throttle a little more about half way up to make it to the top. You never had to slip the clutch or downshift. Grabbing an extra twist of throttle on either machine was very reminiscent of having a shot of nitrous at your disposal—it was that crisp. Even after multiple hill climbs and drag races, we couldn’t get the Wiseco clutch to heat up; that’s a very impressive fact coming from a new product like this.

We didn’t just shoot the hill at Little Sahara. We explored the entire dunes, the surrounding campgrounds and even rode into town. The JSR Performance Yamahas ran flawlessly during our trip. We put them through the wringer, and they came out shining. We only had one failure when test rider Kris Layton was throwing a roost for our camera and the YFZ450R flipped over and bent a tie-rod. Better a tie-rod than a spindle or an A-arm.

JSR Performance not only builds Yamaha engines, they also have experience with Honda and Suzuki powerplants, too. They can sit down with you at their shop or over the phone and discuss what your motor needs are and build you a custom package, not just sell you an off-the-shelf-kit. Visit them online at www.bigboremotors.com or call them directly at (316) 733-1936

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