Making this popular quad new again

By the staff of Dirt Wheels,

Photos by Pat “Ride in focus” Carrigan


There is no doubt that Duncan Racing International (DRI) helps breed winners. Erin Simmons relies on the DRI team of Loren and Leonard Duncan to build and prep his AZOP championship-winning Honda TRX450R.

Going fast in Grand Prix-style racing is no small feat. Having a quad ready to tackle multiple types of terrain is half the battle of competition at a pro-level. Simmons is no slouch on a quad, either. Winning races requires skill, determination, quick thinking, and a sprinkle or two of talent doesn’t hurt. We met with the DRI crew to test a few of their sterling builds, and Erin’s performance racer made the cut.

Roll Design suspension and Elka shocks provide a lot more travel compared to stock and an outstanding ride.

Erin needs a quad that is pro-level race-ready. Honda’s TRX450R continues to compete successfully in many types of competition. The motor can handle a lot of upgrades to produce more power while retaining reliability. Loren Duncan tackles the engine tear-downs, rebuilds, machining, and more for the company. He massaged the Simmons motor with DRI’s National 450cc kit.

Loren used his vast experience to put together a JE piston, X22 Baja camshaft, valves with titanium retainers, valve springs, and valve guide kit that seamlessly work together. On top of that, he expertly ports and polishes the cylinder head, and machines the valve seats. He went a step further and had the crankshaft Cryoheat-treated to reduce friction and wear.

The National 450cc kit also includes DRI’s Fat Boy 4 complete stainless steel exhaust system. Simmons wanted the muffler custom-anodized and powder-coated.

A Works Connection clutch perch has a built-in hot-start lever to get the Honda fired up. A Pro Design ATV kill switch is required for closed-course racing. Oury grips are soft and lessen the chance of getting blisters on your palms.


Once the top-end work was performed, the clutch was massaged. DRI uses its own clutch kit with a Hinson Racing’s clutch basket topped with a DRI quick-change clutch cover. Duncan’s oil cooler kit helps reduce engine heat and keeps power levels up with an assist from Maxima oil.

Once the engine is completed, it’s handed over to Loren’s brother, Leonard, who handles the chassis building. Leonard is also Simmons’ mechanic and preps the race quad for each round of racing. The engine was mounted in a freshly powder-coated TRX frame after a DRI gusseting kit was welded in.

Powder 1 took care of the coating. Before the rest of the 450R was put together, Leonard installed a 41mm FCR carburetor that had a kit from DRI included. Next, a DRI-massaged Vortex X10 programmable CDI box was added. The intake system came from Pro Design with a custom-fitted K&N air filter. That finished off the power parts.

A DRI sprocket guard saves the Sunstar sprocket and RK Excel chain from getting damaged. A Hess Motorsports product protects the rear brake rotor.

We aren’t surprised that Duncan installed Roll Design (RD) products on this build. Roll offers top-of-the-line suspension, steering, and handling components for most ATVs. The stock steering stem was replaced with a +1-inch-taller RD anti-vibe stem. GPR’s V1 steering stabilizer tackles stabilization duties. Roll’s MX Lobo II A-arm kit was bolted onto the frame utilizing OEM Honda spindles.

This kit adds width and more wheel travel than most aftermarket A-arm manufacturers. Roll utilizes Heim joints that allow you to adjust multiple facets of the kit’s alignment to match the terrain you ride in. Attached to the arms are a set of Elka Stage 5 fully adjustable shocks. 

The rear end of the Honda gained the same suspension treatment. The new swingarm is a 1/2-inch longer than the stocker. Elka’s remote reservoir Stage 5 shock and linkage kit found their way onto the Honda. DRI installed the Crown Series steel braided brake lines to replace the stock ones. Leonard matched the new front width, with an RPM rear axle.

The axle is very strong and allows you to change the width as required. RPM’s bearing carrier and anti-fade locknut were also used. 

Roll Design makes a great heel guard, footpeg and nerf bar combination. The footpeg is much wider than stock.


The suspension isn’t the most important handling component. Every piece plays a critical part in getting an ATV to move and steer how you want it to. Mounted atop the Roll Design anti-vibe clamp is a Fasst Company handlebar that utilizes elastomers to lessen vibrations and hard hits to the rider.

Mounted to the bar on the left side is an Oury grip with a Works Connection clutch perch, hot start, and lever combination next to it. You won’t find a control cluster for starting since the quad is kick-started. Powermadd Sentinel handguards protect the controls and Erin’s digits. On the right handlebar, a Motion Pro Vortex twist throttle is preferred.

Elka Stage 5 shocks are connected to Roll Design’s MX Lobo II kit for this Duncan Racing-built Honda TRX450R. A GPR stabilizer keeps the wheels in the right direction.

Renegade race fuel feeds the thirsty engine and is contained in a large 3.7-gallon IMS fuel tank with a dry-break quick-fill setup. Pit stops need to be fast in racing, and a dry-break setup gets the job done in less than half the time.

The OEM plastics were reused with a custom-made DRI/D’Cor graphics kit that shows all of Erin’s sponsors, including his own father’s company, Antelope Slot Canyon Tours. Off-roading is in the Simmons family blood. The stock hood was replaced with a much more stylish FourWerx Carbon white plastic addition.

Loren Duncan pulled apart the entire engine and rebuilt it with their National 450cc kit. They also bolted on an oil cooler to lower engine temps.


Heading downward, the stock seat was recovered with a Pro Top DR seat cover that adds a lot more grip for Simmons’ rear. On the front of the Honda sits a chrome DRI front bumper. Erin uses Roll Design nerf bars and heel guard/footpeg combos on his build for protection from other racers and great foot traction.

Speaking of protection, the bottom of this Honda is covered by a 1/2-inch-thick Campbell Racing Fabrication skid plate. The rear brake rotor is guarded by a Hess Motorsports-crafted aluminum guard. One of our editors still runs that exact guard on his personal racer after two years of success. The new Sunstar rear sprocket and RK Excel chain are protected by a DRI aluminum guard.

The power output of this quad is strong yet easy to wield in the hands of experienced riders.


Climbing aboard a built Honda TRX450R feels like home for us. Simmons’ Duncan-built ride was no exception. Everything worked together flawlessly. That includes the DWT Beadlock wheels wrapped with renowned Maxxis RAZR 2 tires and filled with Tire Blocks.

Once we grabbed a handful of throttle, and the tires found traction in the dry SoCal dirt, the DRI-built motor rocketed us away. The power output is quite potent but not overwhelming. The hit off the bottom is smooth, yet it has a much meatier midrange, and the engine continues to pull through the top end quite hard. We didn’t have any wet dirt to truly feel how strong the torque down low is.

Control is key for any machine, and a motor that is as easy to use as the suspension is supple is going to be a winner. The combination of Roll Design suspension and Elka shocks has won more races and championships than we can count. Erin’s Honda was able to soak up any terrain that we guided it to. The chop was soaked up, whoops were gobbled and landings were smooth. The quad corners just right for Grand Prix racing with enough clearance for rough sections, but it slides the rear controllably and easily.

Overall, Duncan Racing knocked another build-out of the park and never ceases to impress. Their extensive experience in helping Erin Simmons transfer his great skills to the quad and win races! Stay tuned for more builds from their crew.

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1/2-inch skid plate $110


Cryo treatment & micro polishing $375

DOUGLAS WHEEL & TIRE: (800) 722-3746,

Front & rear beadlock wheelset $749

DUNCAN RACING: (619) 258-6309,

Baja frame prep $450

DRI National 450cc kit $2595

FCR 41mm carburetor kit $699

Oil cooler kit $995

DR-C14 clutch kit $199

DRI/D’Cor Simmons SE graphics kit: N/A

Quick-change clutch cover $199

Parking brake block-off $14.95

Chrome front bumper $199

Crown Series steel-braided brake lines:

Front $119.95

Rear $39.95

ELKA SUSPENSION: (800) 557-0552,

Stage 5 front shocks $1,795

Stage 5 rear shock $1,295

Rear linkage $399

FASST CO.: (877) 306-1801,

Flexx handlebar $359.99

Bar pad cover $10

FOURWERX CARBON: (262) 501-9696,

Plastic hood $130

GPR STABILIZER: (619) 661-0101,

V1 ATV damper kit $549

HESS MOTORSPORTS: (940) 759-4597,

Rotor guard $150

HINSON RACING: (909) 946-2942,

Works IH/PP clutch basket $499

IMS PRODUCTS: (800) 237-9906,

3.7-gal. fuel tank w/ dry brake $274.95

MAXIMA RACING OILS: (800) 345-8761,

MAXXIS:, local dealer

RAZR 2 – 21×7-10: NA 

RAZR 2 – 20×11-9: NA

MOTION PRO: (650) 594-9600,

Vortex twist throttle $27.99

OURY GRIP: (800) 333-6879,

Waffle grip $11.99

POWDER 1: (619) 588-9200,

Powdercoat $375

POWERMADD: (651) 462-8465,

Sentinel handguard $40

ATV mounting kit $45

PRO DESIGN: (714) 534-0620,

Pro Flow kit w/ K&N filter $169

ATV kill switch & tether $34.95

RENEGADE RACE FUEL: (800) 733-3381,

RK EXCEL: (760) 732-3161,

O-ring chain $85

ROLL DESIGN: (760) 731-5920,

MX Lobo II A-arms $1595

+ 1/2-inch swingarm: N/A

+ 1-inch steering stem $299 

Footpegs $239

Heel nerf bars w/ heel guards $239

RPM: (928) 771-9363,

Dominator II axle $419

Bearing carrier $249

Anti-fade locknut $219

SUNSTAR: (937) 704-1462,

Powerdrive countershaft  sprocket – 14T $23.95

Rear steel sprocket, 38T $34.95

TIRE BLOCKS: (253) 973-5111,

21×7-10 kit $100 a tire

20×11-9 kit $137.50 a tire


X10 programmable CDI $535 

WORKS CONNECTION:  (530) 642-9488,

Clutch perch assembly 

    w/ hot start $189.95


Pro Top DR seat cover $199

SPONSORS: B&B Auto, Antelope Slot Canyon Tours, Duncan Racing, Roll Design, Elka Suspension, Fat Boy 4 Exhaust, RK, Hinson, GPR, DWT, Faast, Works Connection, CRF



Duncan Racingfastest quadsHonda TRX450RModified 450R