Yamaha’s first-generation YFZ450, introduced in 2004, led the way for all other high performance four-stroke ATVs. It was so far ahead of anything available at the time, a good, well-maintained example can hold its own against today’s most advanced production race quads. Sadly, most high performance machines see hard use and don’t get the maintenance they deserve. We borrowed one of our test riders’ well-worn YFZ450s to see what it would take to bring its performance back.
WHERE WE STARTED
The 2006 YFZ we started with was well setup but well used. Wide A-arms, Elka shocks and a wide rear axle were already in place, and so was a largecapacity fuel tank. If you need the extra suspension travel and stability that aftermarket A-arms and shocks provide, finding a machine that has them can save you the $1500 to $2500 it costs to buy new parts to convert a standard, woods-width machine. Like any machine with lots of hours on it, the suspension was in need of service. Race Tech replaced all the worn shock seals and changed the oil for less than $200 per shock on the front shocks, and serviced and re-valved the stock rear shock for $300.
Our test rider’s YFZ was smoking and down on power when we began, and we discovered the crank was damaged from the engine being run low on oil. Since a full-engine rebuild was needed, we treated it to a fresh top end with Hot Cams high-performance cams; a 478cc, big-bore cylinder; a piston kit from Cylinder Works; and a new crankshaft assembly from Hot Rods. The high-performance parts were actually less expensive than stock parts. For example, the stock crank assembly costs $404. The Hot Rods crank is only $260.99! Yamaha doesn’t offer a complete top-end kit like Cylinder Works, but the original piston and cylinder cost more than the Cylinder Works kit, which also includes the piston rings and top-end gaskets.
The Stage 1 Hot Cams we used for the Yamaha use the stock valve springs. ParaPros assembled the engine and jetted the stock carb to work with the engine mods and performance exhaust. To protect the new engine and provide unrestricted intake, we installed a Uni Filter. FMF’s Powercore 4 titanium exhaust saves weight and lets the cammed, big-bore YFZ engine breathe. A Hinson clutch makes sure all the modified engine’s extra power reaches the rear wheels.
With fresh suspension and the engine running better than new, the YFZ wasn’t just fun to ride, it could perform like a competitive race machine again. All it needed to be ready and reliable for racing were new tires and wheels from STI, pegs and nerfs from Tusk, new graphics, and a new chain and sprocket set from Renthal. Everything that we needed for the Yamaha, including the engine parts, was available from Rocky Mountain Cycle.
ON THE GAS
Our project YFZ soundly outpowers and outhandles the impressive firstgeneration Yamaha it’s based on. The big-bore engine pulls harder at lower revs than the stock engine, and the modified engine’s advantage grows as the revs build. Having more lowend and midrange power makes the modified Yamaha quicker and easier to ride, and the top-end pull is amazing. This machine would work well for cross-country or motocross racing, and it’s a powerful, reliable setup for playing in the dunes too. Your old YFZ may not have the excellent Elka front shocks our test riders did, but Race Tech can rebuild and re-valve the stock shocks from most sport quads so they perform better than new.
Cylinder Works: www.rockymountainatvmc.com, 800-336-5437
3mm big-bore, 478cc cylinder kit(#23001-K01)—$529.99
Kit includes big-bore cylinder, forged Vertex piston, rings and Cometic top-end gasket kit.
Hot Cams: www.rockymountainatvmc.com, 800-336-5437
Stage 1 intake cam (4023-1IN)—$169.99
Stage 1 exhaust cam (4044-1E)—$184.99
Hot Rods: www.rockymountainatvmc.com, 800-336-5437
Main bearing seal kit—$57.99
Cometic: www.rockymountainatvmc.com, 800-336-5437
Complete gasket kit—$65.99
FMF Racing: www.rockymountainatvmc.com, 800-336-5437
Ti Megabomb header—$314.99
4.1 Ti slip-on muffler—$359.99
Uni Filter: www.rockymountainatvmc.com, 800-336-5437
Two-stage air filter—$27.99
Attack Graphics: www.attackgraphics.com, 800-336-5437
Custom graphics kit—From $29.99
Tusk Offroad: www.tuskoffroad.com, 800-336-5437
Footpeg nerf with heel guard—$169.99
Comp series front bumper—$64.99
Rear brake block off—$8.99
Tusk adjustable-width racing axle—$199.99
STI Tire & Wheel: www.rockymountainatvmc.com, 800-336-5437; www.stitireandwheel.com, 318-255-0049
Front: 21×7-10 Tech 4 XC tires—$45.99 each
Rear: 20×11-9 Tech 4 XC tires—$59.99 each
Front: 10×5 Pro-Lite Beadlock polishedwheels—$195.95 each
Rear: 9×8 Pro-Lite Beadlock polishedwheels—$189.95 each
Renthal: www.rockymountainatvmc.com, 800-336-5437
O-ring works chain—$85.99
Dual compound grips—$13.99
CV4: www.rockymountainatvmc.com, 800-336-5437
Formed silicone coolant hoses (SFSMBC29B)—$60.99
High-temp radiator cap (CV715-31M)—$22.99
CV4 lithium racing battery (CV4B003C)—$159.99
Gator guard (CV4-1240)—$89.95
Works Connection: www.worksconnection.com, 800-349-1475
Elite body assembly—$79.95
Elite thumb wheel assembly—$37.95
Hinson Clutch Components: www.hinsonracing.com, 909-946-2942
Inner hub/pressure plate kit—$499.99
Billet clutch basket—$229.99
Clutch fiber steel spring Kit—$199.99
ParaPros: www.paraprosracing.com, 951-544-0882
Motor assembly (SoCal) and setup—$300
Race Tech: www.racetech.com, 951-279-6655
Front shock rebuild—$195 each
Rear shock gold valve re-valve—$300
Moto Seat: www.motoseat.com, 951-258-5229
Custom Cool seat cover—$49.95
Jetting—165 main, 48 pilot, NCVQ 3rd clip, 2 out on the fuel screw, 45 leak jet