In the realm of sportbikes and motorcycle road racing, Yoshimura Research and Development is a proven leader. Over the years it has annihilated the competition, having won more U.S. Superbike Championships than any other race team in the history of the series. But as we recently discovered, its tuning wizardry extends beyond the realm of asphalt and onto the dirt. To prove this it teamed up with Noleen J6 Suspension Technologies. Together they worked their magic on Yamaha’s recently redesigned YZ450F dirt bike.
Out of the the crate, the 2010 Yamaha YZ450F is a great motocross bike. It utilizes first-rate suspension, a responsive yet stable chassis and snappy engine performance which make it one of the easier 450-class dirt bikes to pilot. Only problem is that its design focus (like all motocross machines) is aimed at a broad range of riders. The powerband is biased toward bottom to mid-range performance, its ergonomics cater to average and undersized riders and its suspension set-up, while superb for stock, will need some extra damping for heavier and/or faster riders. So this was goal of this project: Expand the versatility of some components (engine, drivetrain and brakes) and tailor others (suspension, controls) to our personal preference.
Yosh began by reworking the heart of the motorcycle, the rearward-slanted 449cc water-cooled Single. The first order of business was to port and polish the cylinder head to increase the “efficiency” of the engine.
SHOP TALK – POWERTRAIN
Yosh began by reworking the heart of the motorcycle, the rearward-slanted 449cc water-cooled Single. The first order of business was to port and polish the cylinder head to increase the “efficiency” of the engine. This maximizes the flow of fuel and spent gasses in and out of the combustion chamber and allows the motor to generate power in a more linear way. The result is added engine acceleration, power and rear wheel traction. Complementing the cylinder head mod is a new aluminum high-compression piston from CP Pistons which raises the compression ratio from 12.5:1 (stock) to 13.5:1. This boosts power throughout the rev range.
To further enhance exhaust flow it bolted up its top-of-the-line Yoshimura Pro series RS4 Full System exhaust pipe. Carrying a retail price of $1045, the pipe certainly can’t be termed cheap; once you see it you’ll understand why it’s so pricey. Yoshimura prides it’s self on its superb quality and the RS4 system doesn’t disappoint. It is constructed from high-grade titanium and terminates in a sleek tapered carbon fiber silencer. The pipe also features an optional sensor bung for use with the Yoshimura DATA Box (more on that later). The exhaust uses its duplex chamber which works more effectively with the mechanical pulses of the engine thereby increasing power output. If you want some extra power but aren’t as concerned with weight or super trick appearance, Yosh offer it’s more reasonably priced RS-4 Comp Series Full Systems too.
With the introduction of electronic fuel-injection, tuning the engine’s fuel and ignition settings can be done with more precision than ever before. The Yoshimura Peripheral Interface Module 2 (PIM2) is a plug-and-play electronic box that piggy-backs with the stock ECU and allows you to alter the engine’s fuel map on a Windows-compatible computer.
As opposed to the Yamaha’s GYTR Power Tuner (read the review in the Yamaha GYTR Power Tuner Review), the PIM2 gives you far more adjustability. The fuel curve can me modified in 500 rpm increments at 10% throttle angle intervals.
With the throttle wrapped to the stop, the engine piles on revs much faster than stock. It’s actually incredible how snappy engine response with it spinning up with a similar feeling to that of a brand-new 250F.
The PIM2 works in unison with the Yoshimura Data Box which consists of an air/fuel sensor that screw into the bung located on the exhaust pipe. The system then monitors the air/fuel ratio of the engine and can be set to automatically adjust the fuel curve setting based on the user selectable target air/fuel ratio. This ensures that the engine will always run perfectly regardless of type of fuel, weather, elevation, or track conditions. Welcome to the digital dirt bike age folks.
Our engine was programmed with a custom map developed by Yoshimura for use with its modified cylinder head and full exhaust system at Southern California’s Glen Helen Raceway and Milestone Motocross Park. The map will also soon be available under the Engine Management Download section on its website.
To make certain the engine runs as cool as possible a set of replacement coolant hoses were sourced from CV4 Products. The hoses (available in a multitude of colors) are designed to be more durable while also adding an element of style to the motor. Lastly a Yoshimura Case saver was bolted on to protect the engine case near the countershaft sprocket from rocks kicked off by the chain. Speaking of the chain we replaced the stretched out stocker with a gold DID ERT2 that spins a one tooth bigger (49 tooth) aluminum drive sprocket from Tag Metals. We fitted a slightly bigger rear sprocket to reduce the gap between each of the five drive gears.
While we’ve never had any major issues with the stock transmission we’ve noticed that it feels tight and doesn’t move between each gear as smoothly as other bikes in its class. Yosh addressed this by applying its In-house Superfinishing Process (ISF). ISF is a special friction-reducing coating that is applied to moving parts, in this case the transmission gears. It’s the same treatment that Yosh uses to help free extra horsepower in its Suzuki GSX-R1000 Superbike engines. It’s similar in effect to hand-polishing but it’s far less labor intensive which makes it much more cost effective than ever before. This helps make each gear mesh more smoothly and allows the transmission to operate more freely.
The clutch was also upgraded with new hard parts from Hinson Racing Clutch Components. Internally, a new clutch basket, hub, pressure plate and springs were installed. Compared to stock parts the Hinson components are manufactured with perfectly machined aluminum bits and coated with a finish that allows the clutch to spin more effectively thereby reducing drag and heat and extending clutch life. Externally we fitted its bomb-proof hard anodized clutch and generator covers that not only hold up against crashes better but don’t show wear with use.
SHOP TALK – CHASSIS
(Above) As the fork and shock compress deeper into its stroke the compression was slowed down to better control chassis pitch under medium-to-heavy loads. (Below) Next to the reasonable price, with both the fork and shock being serviced and re-valved for only $375, the best thing about Noleen is that it covers its work with a 45-day warranty.
For the suspension modifications, Yoshimura recruited the expertise of the folks at Noleen J6 Suspension Technologies. Based on our weight (165 to 175 pounds) and skill (novice-to-intermediate), Noleen recommend that we retain the stock spring rates (0.47 kg/mm front, 5.7 kg/mm rear) and went about trying to achieve added suspension functionality by modifying the speed in which the oil flows inside the fork and shock via valving.
The low-speed compression front and rear was made more responsive which would help absorb impacts at the initial phase of suspension stroke. As the fork and shock compress deeper into its stroke the compression was slowed down to better control chassis pitch under medium-to-heavy loads. The shock’s high-speed rebound circuit was also slowed down while the fork rebound setting was unchanged. The fork was then filled with Alurion 5WT oil while the shock was topped off with Maxima 7WT fork fluid and recharged with nitrogen.
Next to the reasonable price, with both the fork and shock being serviced and re-valved for only $375, the best thing about Noleen is that it covers its work with a 45-day warranty. So if at any point you’re not satisfied with the way the suspension performs bring it back and they’ll get it sorted based on your input.
The potential for more speed means the need for added braking power. So Yosh fitted an Braking Batfly 270mm Oversized Front Rotor Kit. The kit includes the rotor and relocation bracket for the twin-piston front caliper and a pair of high-friction brake pads. The name of the kit stems from the unique shape of the disc in which black grooves on the rotor track are designed to more effectively dissipate heat. Also installed was a Yoshimura Brake Clevis engineered to increase rear brake feel.
In terms of rider comfort a tall-guy compatible Kevin Windham-bend ProTaper handlebar replaced the stock ProTaper bar. A Works Connection Elite clutch perch was also added. To help protect the engine the stock plastic skid plate was replaced with an aluminum part also from Works Connection. Lastly, to ensure we were hooked up on the track we mounted a set of Dunlop’s versatile and reasonably priced Geomax MX51 intermediate terrain tires in OE sizes (90/100-21 front, 120/80-19).
To find out how this hopped-up YZ450F performed we rode it at a variety of tracks all around Southern California. The author, along with our pro-level test rider Chris See spent a few days pounding out motos at tracks like Milestone Motocross Park and Perris Raceway. Milestone and Perris share similar dirt composition (soft and tacky) and are characterized by a variety of different small-medium-and large sized obstacles, deep ruts, and have a fast flowing layout that that doesn’t develop a whole lot of bumps or chop. So in order to subject the chassis to higher levels of abuse, we also rode at rough, bumpy and fast tracks like the now defunct LACR and Glen Helen Raceway.
Our Yoshimura-prepped Yamaha YZ450F is one of easiest (and fastest) motocross bikes we’ve ever ridden.
In spite of the engine employing an 8% higher compression ratio, it is still fairly easy to get fired with one or two well-timed kicks of the kickstart lever. While in stock form the Yamaha offers handlebar position adjustability with its clever pre-drilled handlebar mounting holes on the top clamp, the problem is the stock bar is a low bend. This makes it hard for taller riders (6-foot and above) to get comfortable at the controls—especially over jumps. But with the addition of the Windham-bend ProTaper bar, the ergos become far more accommodating.
Pin the throttle and you’ll instantly notice how much smoother the bottom-end power is. It actually feels maybe just a hair more mellow than stock but the important aspect is that it isn’t anywhere near as abrupt as the stock bike which allows the rear Dunlop tire to hook-up incredibly well out of a slow speed corner.
With the throttle wrapped to the stop, the engine piles on revs much faster than stock. It’s actually incredible how snappy engine response with it spinning up with a similar feeling to that of a brand-new 250F. If you’re looking for a big power hit or arm pulling rush of torque you won’t find it here. It’s simply ridiculous how smoothly the engine pumps out torque. If the roar of the air intake and bark from the exhaust wasn’t so loud you could possibly think that it’s actually slow—the engine produces power that smoothly. This results in incredible drives out of ruts. In fact this bike “hooks-up” better than any motocross bike I’ve ridden lately. We also noticed much more freely the bike shifted between each gear.
“It’s one of the smoothest bikes I’ve ever road,” states Chris “If you want to grab a gear and jump a triple right out of the corner this bike will to do it. The engine is so strong that it really makes everything up to you. You never have to second guess yourself on this bike. It’s got such smooth versatile engine that it’s perfect for a Vet rider or a faster young buck like me. I’d say it’s not really a beginner bike because it’s got some beans.”
Another area of the powerband that the stock YZ450F has problem in is its top-end with power tapering off slightly as it closes in on redline. The Yosh engine however makes this area of the powerband feel night-and-day different. The engine pulls to redline with far more urgency and continues to pump out power even during over-rev—incredible!
(Above) One of the biggest attributes of our modified YZ450F is how well it hooks up out of the corner.
As with the stock set-up, clutch lever pull action is light but what we were really impressed with is just how responsive it felt when fanned with your finger. With so much more power at your disposal at times you’re going to need to work the clutch in order to modulate power, say when you accelerate out of a corner or as the bike starts to wheelie. It’s actually really difficult to put in words how the clutch feels. But the biggest thing is that its feel and the point at which it engages/disengages is consistent whether you’re on the first lap of your moto or the last and that in turn helps elevate the rider’s confidence in his machine.
In terms of chassis the front Dunlop MX51 tire complements the handling of the bike well. The front end turned with precision and tracked well in and out of ruts and walled berms. Per Noleen’s recommendations we set rear sag at 105mm. The front-to-rear balance of the chassis felt good with both ends offering a high level of pitch control.
Due to how smooth and relatively bump-free Milestone and Perris are it is hard to get a good read on the suspension as it performed perfectly there. But after riding at LACR and Glen Helen we continued to be believers. We had to add compression damping at both ends but rebound was unchanged. Both the fork and the shock do a superb job of filtering out the effects of bumps and chop which in turn helps save the rider’s energy allowing them to ride harder longer.
Overall we like the way the suspension moved but we ran out of adjustment range with the fork and felt that it was slightly under sprung. So for the next phase Noleen is going to go up one on the spring rate. For the most part the chassis remained stable but occasionally we did encounter some headshake when were racing down Glen Helen’s steep downhills but again we think that the solution might be higher fork spring rate.
“It’s one of the smoothest bikes I’ve ever road,” states Chris “If you want to grab a gear and jump a triple right out of the corner this bike will to do it.
Braking performance was a substantial increase over stock. I remember a few times coming into a corner hot and wondering if I was going to be able to slow down enough to pitch it into an inside rut. Despite my apprehensions every time the bike shed speed controllably and I nailed my line. Perhaps the coolest thing about the oversized rotor is that it doesn’t make the brake feel any more grabby or hard to modulate. It just feels like it delivers more clamping power for the same amount of lever input. We were also impressed with the added level of feel. Conversely out back we couldn’t ascertain any change in rear brake feel with the trick-looking Yosh brake clevis.
We always knew that Yoshimura made good stuff however we’re simply blown away by the performance of our YZ450F project bike. Perhaps even more impressive is how it manages to make that performance accessible for a novice rider like me and a pro-level racer like Chris. Never before in my life have I been able to put burn through a full tank of gas in one moto—until now. This Yamaha is so easy and entertaining to ride that it will encourage you to ride, ride, and ride until you’re literally running on fumes. Stay tuned for our follow-up story in which we race it in this weekend’s MTA World Vet Championships at Glen Helen Raceway.