By the staff of Dirt Wheels
RACE-READY YFZ450R. What it takes to be a champion: skill, talent, strength, commitment, motivation, courage, endurance, and much more. That’s the stuff WORCS 2018 ATV Pro Championship winner Mile Sloan is made of.
However, some of the most crucial aspects of a pro racer’s program are a machine that is built for battles and a team that supports the effort. Duncan Racing International has been in the pages of Dirt Wheels quite a lot throughout 2019 and 2020 issues.
That simply stems from their expertise, experience, and the fact that they are providing great builds for us to cover. Leonard Duncan and his older brother Loren are the brains behind Mike Sloan’s build, and Lenny tackles the race-to-race rebuild and maintenance for Sloan’s Yamaha YFZ450R.
Bringing a bare-bones build to a full-blown racer is no easy feat, but as you may have seen before, Duncan Racing is equipped for the task. Mike’s sponsors also provide his program with some of the best components in the industry.
This racer started off as a 2017 Yamaha YFZ450R. It is wide and ready to go fast in stock form, but DRI and Sloan felt it needed a lot of new parts to better handle the aggressive terrain of the Grand Prix-style WORCS racing series.
The frame was stripped of all the stock parts, and the subframe was exchanged for a Lonestar Racing adjustable version to help lower the seat height of the YFZ. Many racers have tested different seat/subframe heights to help with cornering and traction.
In order to start making the frame a roller, the stock swingarm was reinstalled, but the stock axle was swapped out for a stronger RPM Dominator II that is width-adjustable. An Elka Stage 5 remote reservoir shock suspends the swingarm with the help of an 8mm-longer Roll Design linkage.
Upfront a pair of Elka Stage 5, dual-compression, spring-preload, and rebound-adjustable shocks are connected to the frame and a set of long-travel Roll Design A-arms. Roll Design dialed in Mike’s Elka shocks to the specifications he requires for his riding style, weight, terrain, and more.
The stock spindles and hubs were mounted to the RD arms with Walsh Race Craft pins. A Roll Design +1-inch-taller steering stem found a home on this build with an RD handlebar clamp. A GPR steering stabilizer is attached to the Roll Design stem to keep Sloan on track in the roughest of conditions.
The front of the YFZ gained a chrome Duncan Racing bumper. Rath Racing sponsors Sloan and provides his build with its Signature Series nerf bars with Monster Pegs included. Foot traction is insanely good on the tall, sharp teeth of the Monster pegs, which also expand to the full width of the nerf bars.
Leonard mounted a Rath Racing rear-number-plate grab bar to the LSR subframe. The bottom of the Yamaha’s frame gained a Campbell Racing Fabrication 1/2-inch-thick poly skid plate.
MAKE THE PASS
Duncan was able to set Mike Sloan’s Yamaha on the ground with a set of Maxxis RAZR 2 front and RAZR XC rear tires, wrapped around DWT Racing G3 beadlock wheels. Danny Prather Tire Balls’ flat-prevention system fills all four tires with inflatable rubber balls on this racer. Galfer brake rotors assist the stock calipers and DRI’s Crown Series steel-braided brake lines in slowing Mike’s fast motion. The YFZ’s stock handlebar was tossed aside for the installation of the impressive Fasst Company Flexx handlebar, which has a hinge and elastomer system to lessen vibration and hits through the quad.
The stock front-brake perch and lever were reinstalled, while a Works Connection reservoir cap replaced the stock one. A new Works Connection clutch perch found its way onto the Flexx bar. Yamaha’s thumb-throttle assembly isn’t the right fit for everyone. Sloan prefers a thumb throttle from a Honda TRX90X. A set of Powermadd Sentinel handguards protect Sloan’s knuckles from roost. Oury grips round out the handlebar and control setup.
Protecting Mike’s YFZ450R is important. The stock swingarm’s plastic skid plate is made of plastic that won’t survive a rough and rocky WORCS race. DRI custom fabricates a swingarm skid plate that protects the brake rotor and has a built-in chain guide. An aluminum guard from Duncan protects the Sunstar sprocket and RK Excel O-ring 520 ATV chain.
Yamaha’s engine makes impressive power stock, but once Loren Duncan gets done massaging it, power and torque output is greatly increased. DRI offers their HP4 valve-train kit that comes with head porting, SERDI valve seat machining, billet camshaft, heavy-duty valve springs, HP guides, and a big valve kit.
A custom high-compression JE Piston is installed that requires running race fuel. Sloan utilizes VP Race Fuels fed from a 3.2-gallon IMS desert tank with a dry-break. DRI takes the OEM crankshaft and trues it for smoother operation. Then, a high-capacity billet oil cover from Zip Racing is mounted up that holds 8.5 more ounces of Maxima oil. DRI offers an aluminum oil-catch can that replaces the stock plastic version.
Sloan’s Yamaha is outfitted with a complete Hinson Racing clutch kit that includes a billet basket, inner hub, clutch pack and high-capacity cover.
When the engine is in place, the rest of the new performance power parts can be installed. DRI relies on Fuel Customs intake systems that work very well with Yamaha ATVs. DRI installed a Vortex C10 ECU with proprietary Duncan maps loaded in. Exhaust flow is upped via a DRI Fat Boy 4 complete stainless steel system. All of these parts run best after Sloan gets his YFZ450R on PEP Performance Tuning’s Dyno for a final tune.
Mike Sloan has been racing WORCS in the Pro ATV class for a few years now. WORCS offers Grand Prix racecourses spanning from California to Utah, which includes Nevada and Arizona. The courses offer brutally rough terrain at times. Rock gardens, sand dunes, deep whoops, hill-climbs, motocross jumps, tracked out turns, and much more litter each course.
Bring on competitive pro riders and the going gets tough. Mike Sloan managed to earn himself the Pro Championship title and ran the number-one plate all of the 2019 season. This wouldn’t have been possible without his well-oiled team with Duncan Racing International and other sponsors like B&B Auto, Roll Design, and Antelope Slot Canyon Tours.
We didn’t ride Mike’s Yamaha YFZ450R, but we have ridden Duncan YZFs, so we know that the long travel Roll Design A-arm kit and Elka suspension soak up the hardest hits, heaviest landings, and every little bump in between.
The GPR stabilizer is a giant factor in keeping the wheels pointed where you want to go, and you can dial the stabilizer in for different courses. The power output of the DRI massaged engine is something fierce. Torque off the bottom is explosive and would be a handful once your body gets tired.
The horsepower keeps the quad pulling hard through the top of the range. There is a meaty midrange, mainly where you keep the quad throttled while racing. The power is much more controllable with the Hinson Racing clutch. It operates smoothly, and you can easily tell where the friction point is.
The Rath Racing nerfs and pegs keep your feet where you want them, and the Zip Pro Top seat cover does just the same for your behind. One of our favorite aftermarket parts is the Flexx handlebar. Any time we have installed the bar we still are surprised at how much smoother a ride we gain from it.
Mike Sloan’s racer wouldn’t be going anywhere without the traction and flat prevention gained from the Maxxis, Tire Balls, and DWT setup. The Maxxis RAZR 2 and XC tires are some of the best sets in the industry and are utilized by many riders and racers to gain traction in multiple types of terrain.
We hope to see Mike Sloan topping many more podiums and earning more championships in his Pro ATV WORCS racing career. We are once again impressed by another well-built Duncan Racing International quad. They know their way around a Yamaha YFZ450R!
Also, check out this epic DUNCAN DUNER 450R
PARTS LIST: RACE-READY YFZ450R
Campbell Racing Fabrication: (435) 632-4902, www.campbellracingfabrication.com
1/2-inch skid plate $125
Douglas Wheel & Tire: (800) 722-3746, www.dwtracing.com
Front and rear Beadlock wheelset $749
Duncan Racing: (619) 258-6309, www.duncanracing.com
Fat Boy 4 complete stainless exhaust $699
Complete engine rebuild $795
HP4 valve train kit $1649
Custom JE piston $235
Aluminum oil catch can $139
Crown Series brake lines:
D’Cor graphics kit $149
D’Cor number plates $89.95
Sprocket/rotor guard/chainguide $500
Chrome front bumper $199
Elka Suspension: (800) 557-0552, www.us.elkasuspension.com
Stage 5 front shock $1,795
Stage 5 rear shock $1,295
Fasst Co.: (877) 306-1801, www.fasstco.com
Flexx handlebar $359.99
Bar pad cover $10
Fourwerx Carbon: (262) 501-9696, www.fwcarbon.com
Carbon hood $130
Fuel Customs: www.fuelcustoms.com
YFZ450R intake w/ K&N filter $325
Galfer Brakes: (805) 988-2900, www.galferusa.com
Brake rotors $112 each
GPR Stabilizer: (619) 661-0101, www.gprstabilizer.com
V1 ATV damper kit $549
Hinson Racing: (909) 946-2942, www.hinsonracing.com
Billet proof clutch basket $259
Inner hub, pressure plate $525
Clutch kit $199
Extra capacity billet Q/C cover $199
IMS Products: (800) 237-9906, www.imsproducts.com
3.2-gal. fuel tank $274
Add dry-break $256
Lonestar Racing: www.lsracing.com
Adjustable subframe $575
Maxima Racing Oils: (800) 345-8761, www.maximausa.com
10W-40 Premium 4 $7.95 a bottle
DOT 4 Brake fluid $6.95 a bottle
Chain wax $7.50 a can
Maxxis: www.maxxis.com, local dealer
RAZR 2 fronts, 21×7-10 N/A
RAZR XC rears, 20×11-9 N/A
PEP Performance Tuning: (909) 477-7025
KTM throttle body: N/A
Powermadd: (651) 462-8465, www.powermadd.com
Sentinel handguard $40
ATV mounting kit $45
Powder 1: (619) 588-9200, www.powder1.com
Pro Design: (714) 534-0620, www.prodesignracing.com
ATV kill switch & tether $34.95
Rath Racing: (320) 234-7223, www.rathracing.com
Signature series nerf bar w/ monster peg $474.95
RK Excel: (760) 732-3161, www.rkexcelamerica.com
O-ring chain $85
Roll Design: (760) 731-5920, www.rolldesign.com
+1-inch steering stem $299.95
Anti-vibe clamp $99.95
RPM: (928) 771-9363, www.team-rpm.com
Dominator II axle $417
Sunstar: (937) 704-1462, www.sunstar-braking.com
Powerdrive countershaft sprocket – 14T $23.95
Rear steel sprocket, 38T $34.95
Tire Balls: (502) 243-1601 x1, www.tireballs.com
21×7-10 kit $100 a tire
20×11-9 kit $137.50 a tire
Vortex Ignitions: www.vortexcdi.com
X10 ECU $699
Works Connection: (530) 642-9488, www.worksconnection.com
Clutch perch assembly $149
Front brake master cylinder cap $39
Engine plug kit $49
Zip Racing: www.zipracing.biz
Pro Top DR seat cover $199
High capacity oil cover +8.5oz $249
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