PROJECT ATV : Mike Sloan’s WORCS champion 

By the staff of Dirt Wheels

Mike relies on his Maxxis tires, DWT Racing Beadlock wheels, and Tire Balls to keep him moving through every race.

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.

Rath Racing’s Signature Series nerf bars are very protective, and their Monster peg has sharp teeth for great foot traction. Hinson’s clutch kit is an impressive addition.


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.

Duncan Racing’s oil catch can keeps the Yamaha engine from blowing out too much oil during rough riding. The Zip high-capacity oil cover offers 8.5 more ounces of capacity, and the Works Connection engine plugs are a nice touch.



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.

A large increase of exhaust flow is due to Duncan’s Fat Boy 4 stainless steel full exhaust system.



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.

Fasst Co. Flexx bar smooths out vibrations with ease. The Works Connection brake reservoir cap is a nice touch, and the Powermadd guards protect Mike’s hands.


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.

Duncan Racing offers a stylish chrome front bumper for a lot of different ATVs. The Roll Design and Elka setup is a great combination for a smooth ride.



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.

Sloan prefers to run a Maxxis RAZR XC tire. The DWT Beadlock wheels are used by many racers due to their strength and ease of maintenance.

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.

Zip’s Pro Top seat cover has grippy material on the sides and ridges on top that help keep the rider in place. Yamaha’s slim body makes moving around the quad easy.


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

Having an adjustable subframe will allow you to lower your seat height so you can lean further back on your machine. Lonestar Racing provided the subframe for this build.





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:

Front $129

Rear $39

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

Powdercoat N/A

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

A-arms $1599

+1-inch steering stem $299.95

Anti-vibe clamp $99.95

Linkage $100

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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