**Editors Note- Test from our DEC 97 issue.
Pair of Duncan Doughnuts.
When it comes to reliable performance, Duncan Racing is extremely confident of the products that it sells. So confident, in fact, that it offers a 30-day, 100% money-back guarantee with all of its performance products. If you are not happy with the performance, quality, or reliability of any Duncan Racing product, send it back and your money will be refunded.
We wanted to put Loren Duncan, the owner of Duncan Racing, to the test, so we had his shop modify our stone-stock Honda 300EX and Yamaha Warrior for a comparison shootout. We wanted to see for ourselves if his guarantees stood up to our demanding standards. We told Loren we wanted both machines to run stronger, without sacrificing reliability, and not to make them “race”-only motors. Both machines should be all-around better play quads that could be “play”-raced but had tractable and easy-to-ride powerbands. Loren accepted our challenge willingly.
DR equipped both our 300EX and Warrior with its “National” package engine performance kits. This consists of a hotter cam, porting and three-angle valve job, heavy-duty valve springs with chromoly tops, Wiseco high-compression piston, SuperTrapp exhaust system, Keihin 38mm PE carb, K&N air filter, and Outerwears filter cover. The Warrior also gets a Pro Flow air cleaner flange. All of this costs $1149 for the 300EX and $1089 for the Warrior. For an additional $60, DR will also machine the stock flywheels for quicker revs and smoother power.
CHASSIS MODS FOR THE HONDA
Our TRX 300EX was outfitted with a Dominator axle ($369.95) and RPM Twin Row Axle Carrier ($199.99) with an anti-fade axle lock nut. A set of RPM Taper lock hubs ($249.95), a trick DR steering damper ($199), Renthal aluminum handlebars ($69.95), a Tsubaki Omega O-Ring chain ($97.04) and a 14-tooth countershaft sprocket ($17.95) were also installed on the EX. OMF supplied a swingarm skid plate ($89.95) along with the engine skidplate ($54.95) for the machine.
Other bits and pieces on the EX were a DR chrome bumper ($124.95), a DR handlebar clamp ($29.95), DR shock cover ($40 per set), DR steel-braided brake lines (front, $84.95; rear, $29.95), DR aluminum nerfs ($140), DR billet throttle cover ($39.95) and Douglas Black Label wheels with OMV reinforcement rings and Holeshot tires on the front and back (21×7-10 front, 18×11-8 rear).
CHASSIS MODS FOR THE YAMAHA
Our Warrior also came with all the same chassis components as the Honda EX, with the addition of an RPM axle locknut ($54.95), an aluminum DR rear grab bar ($33), and an OMF Glyde skid plate ($54.95). It also came equipped with Douglas Black Label wheels with OMF reinforcement rings and ITP Holeshot tires on the front and back (22×7-10 fronts and 20×11-9 rears).
Maxima engine oil and brake fluid were used in both machines along with Trick Racing gas. Loren Duncan likes to use the high-octane Trick gas for his machines but says that either machine can be run with high-octane pump gas with no ill effects.
PUTTING THEM TO THE TEST
To see how well these modified sport quads performed, we took them out to Glen Helen Raceway for an extensive track testing session. Our test crew did laps aboard each machine separately, then faced them off against one another. We wanted to determine how well each one accelerated, how smooth the power came on, where it signed off and which one hooked up the best.
Since we had left the suspension stock on each machine we had to be careful in the gnarly whoop sections. The increase in power on both machines made both of them much harder to control in the rough parts of the course than before. With the increase in power, these kits give your machine you have to do something to offset this with some suspension improvements. We plan on beefing up and replacing the suspension components on the EX and the Warrior in an upcoming issue to keep pace with the increased engine performance.
Pair of Duncan Doughnuts
In the battle of engine displacement, the stock Warrior engine already has a substantial edge in size, displacing 348cc to the Honda’s 281cc. Tech-wise, the Honda has the benefit of a four-valve engine design over the Warrior’s dated two-valve design. In the battle of carburetion, the stock Warrior also has the edge, with a 36mm Mikuni over the Honda’s smaller 32mm Keihin. The Warrior also has a six-speed gearbox over the Honda’s five-speed box. This gives the larger-displacement, bigger-carbed Warrior the edge in a stock-versus-stock engine shootout.
Duncan Racing’s engine performance packages for the Warrior and the EX continue this battle among these sport quads. Each machine is on equal footing, carb-wise, with DR’s 38mm Keihin carbs being installed on both. The porting, cams, valve jobs, and exhaust systems on the two machines help broaden and strengthen the existing powerbands without any apparent loss of reliability. The big difference, though, is how much the Warrior engine comes alive with the DR engine kit.
“Our engine performance packages for four-strokes are designed to increase the power and smoothness of the existing motor,“ says Loren Duncan. “It is essential to use [the highest-quality] components possible to make a four-stroke run better. Unlike a two-stroke motor, you have to spend twice as much to get half as much power increase in a four-stroke. You have to be careful to balance the power increase against future reliability.”
WHICH IS FASTER?
In straight-up drag races, the DR Yamaha Warrior was able to retain its displacement edge and clearly beat out our modified Honda repeatedly. The power came on about evenly with both motors, but the Warrior had the edge throughout the power spread, and it revved out further. The modified Honda felt like it hit hard and accelerated quick, but the modified Warrior was able to smoke it virtually anywhere on the power curve and rev out just that little bit further. This gave the Warrior the nod for smoothness and top speed, but the Honda still hooked up and revved until the rev limiter kicked in and stopped it short.
Even though the Warrior had the overall edge on power in our modified shootout, our test riders actually preferred the Duncan Honda when racing on a tighter, more technically challenging track. The Duncan FourTrax had the snappy power, and its quicker and more aggressive handling chassis made it accelerate and power through the turns better than the slower-turning Warrior.
Pair of Duncan Doughnuts
Our test crew came away impressed with how well both machines ran. The Duncan-modified Warrior had beaucoup power everywhere and out revved the modified Honda, but the FourTrax came on hard and could be ridden faster on a shorter, tighter course. Both machines had considerably broader and stronger hits on the low, mid, and top ends of the powerband than their stock counterparts, but the DR Warrior had the biggest increase.
Overall, we would say that larger and heavier riders (over 175 pounds and six feet tall and over) might prefer the modified Warrior for its tractor-like torque, awesome power increase, and easy rideability. Lighter or smaller riders (under 175 pounds and 5’10” or less) might be happier on the quicker-handling, modified Honda EX. Either way, you will have a machine that runs considerably stronger and is much more fun to ride than your stocker. Would we be happy enough to let Loren keep our money for both engine mods? You betcha!
For further information contact Duncan Racing.
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