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Premium Member
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Discussion Starter · #1 ·
[ame="http://www.youtube.com/watch?v=9HxSw-FCv8U"]YouTube - 2010 YZ450F intro[/ame]

Details have emerged on perhaps the most hotly anticipated motocross motorcycle for next year: The 2010 Yamaha YZ450F. Off-road and motocross riding enthusiasts have been buzzing in anticipation of this new dirt bike and Yamaha hasn’t disappointed. Next year its top-of-the-line YZ machine is radically changed with an all-new engine and chassis.

For 2010 the YZ450F’s engine employs revolutionary new ideas we’ve never seen on a Japanese motocross bike. The first thing you’ll notice, besides its sharp new angular bodywork, is the way the 449cc liquid-cooled Single is positioned in the frame. It’s canted rearward for two reasons. First to exploit combustion force and second to keep the bikes reciprocating mass as centered and low as possible. You’ll also notice that the exhaust now exits from the rear of the engine. This was done in order to maximize the engine’s intake and exhaust efficiency by offering a direct path for both fuel and exhaust to flow through the engine.

The bike’s air intake system has been relocated to the front of the bike underneath the fuel tank just like on Yamaha’s YZF-line of sportbikes. A 12-hole fuel-injector shoots fuel into the 44mm Keihin throttle body attached to the front of the engine. It’s powered by a battery-less high input generator that is powered as soon as the kick start is touched.
The cylinder utilizes a bigger bore, shorter stroke format (97.0 x 60.8mm) with a higher compression ratio (12.5:1). A new 4-valve cylinder head replaces last year’s 5-valve component, and, in conjunction with the shorter piston stroke reduces the overall height of the engine. A new “tornado” exhaust system snakes trough the rear of the bike and is designed to complement the new engine’s power characteristics. The 5-speed transmission and cable-actuated wet clutch has also been updated for improved feel and shifting performance.

This cut-out shows the new 1.6 gal. fuel tank, relocated for 2010 on the YZ450F to underseat.
A new aluminum frame and swingarm are used, with the main frame constructed out of sixteen different pieces of aluminum designed to provide optimum rigidity and feel. The entire rear suspension was reengineered in order to keep the rear shock in the center of the machine, a position previously used by the airbox (now repositioned to the front of the motorcycle). Another big change is the way the 1.6-gallon fuel tank has been re-located under the seat between the frame rails.

Reworked triple clamps hold last year’s ultra-plush Kayaba Speed Sensitive fork and reduce offset down to 22mm (from 25mm). The fork also benefits from 10mm longer suspension stroke, updated damping characteristics and still offers both compression and rebound damping adjustment. The rear shock absorber, also made by Kayaba, gets a larger 50mm diameter piston and a larger volume gas reservoir. Like always, it offers adjustment for spring preload, high and low-speed compression, and rebound damping. Lastly, a new lightweight skid plate mounted beneath the engine helps protect the underside of the machine.

Factory GYTR Accessories
Yamaha is releasing an entire line of factory designed and tested accessories to complement your new YZ. Some of the most notable upgrades are the GYTR Ported Cylinder Head Assembly, (the same one James Stewart uses in AMA Supercross) and a GYTR Power Tuner. The handheld unit allows you to adjust your 2010 YZ450F’s engine settings including both fuel and ignition curves anywhere with a push of the button.

Pricing and U.S. availability has yet to be announced. Motorcycle USA will sample the new YZ450F later in September at the legendary Budds Creek Motocross Park in southern Maryland. Stay tuned for the full ride report.

The 2010 Yamaha YZ450F looks ready for dirt and we are looking forward to doing a full-test very soon.

2010 Yamaha YZ450F Specs
Engine: 449cc Liquid-cooled 4-Stroke Single; 4-valve
Bore and Stroke: 97.0 x 60.8mm
Compression Ratio: 12.5:1
Fuel Delivery: Fuel-injection
Transmission: 5-speed; cable actuation
Front Suspension: Kayaba Speed Sensitive; 2 way-adjustable for compression and rebound damping; 12.2 in travel
Rear Suspension: Kayaba gas charged shock absorber; 4-way adjustable for preload, high/low-speed compression, and rebound damping; 12.4 in. travel
Front Brake: 250mm disc with twin piston caliper
Rear Brake: 245mm disc with single piston caliper
Tires: 80/100-21 Dunlop D742FA, 120/70-19 D756
Seat Height: 39.3 in.
Ground Clearance: 15.0 in.
Fuel Capacity: 245 lbs.
Color: Team Yamaha Blue/White; White Red
Warranty: 30-days

source: Motorcycle News and Motorcycles - Motorcycle USA

2,476 Posts
That's a weird way to do the exhaust. I always thought that the straighter the pipe the better as far as perforamce goes, but these guys have the pipe going in a loop before it gets to the can. Weird

82 Posts
That's a weird way to do the exhaust. I always thought that the straighter the pipe the better as far as perforamce goes, but these guys have the pipe going in a loop before it gets to the can. Weird
It also boils down to a "Tuned" length of pipe for proper performance....
only way to gain this length with the given chassis layout.

I wonder what the vibes are like with the cylinder canted rearward?:ermm:

Premium Member
924 Posts
Discussion Starter · #9 ·
The Perfect 10?

Here's an article/review I found about the new YZF450:

Just 12 years ago Yamaha dropped a bomb on the motocross world: Not only would the company release a four-stroke motocrosser to the public, it would laugh at what was considered to be four-stroke doctrine at the time. For those of you too young to remember, four-stroke motocross machinery at the time-when there was any-came from Europe or was handmade by specialty shops, and the rules allowed four-strokes up to 550cc to race in the 250cc class against two-strokes. Yamaha opted for a five-valve 400, and the public couldn't imagine how a four-stroke that small could compete. Yamaha proved everyone wrong, and the company appears ready to attempt a similar lesson in 2010.Without reinventing internal combustion, the '10 couldn't be a more radical departure from existing Yamaha motocross technology and practice. The wheels and one brake are the only carryovers from the existing YZ line. All other parts of the 2010 YZ450F are new and redesigned. As it did with the original YZ400F, Yamaha chose not to bow to convention. The 2010 chassis and engine were designed together for what Yamaha calls an "ideal rigidity balance." This chassis is made up of cast, forged and extruded parts for a total of 16 components formed into what Yamaha has termed a "double S-beam" design. To us mortals it means that the side spars have S-curves when looking at them from the side and also when looking down from the top. The open spars at the top of the frame look narrower near the steering head than examples from other brands.
The body parts and engine look more exotic since the air intake and airbox are at the front of the frame with the filter unit being under the fuel tank in a direct line below the gas cap. Yamaha leaned the top end of the engine back slightly, and the tunable 44mm Keihin throttle body fuel injection gets a straight shot to the now four-valve cylinder head. Yamaha claims that with FI, two intake valves worked better than the three it has used for 12 years.
Yamaha did much more than lean the cylinder and head back; the engine is all-new with a shorter stroke, larger bore and the crank set deeper in the engine cases so the portion of the cylinder that shows looks like it is 20 percent shorter than the 2009 cylinder. In addition to being set deeper, the crank is offset to the rear of the cylinder. This is common in street engines, and it both saves on friction loss and minimizes side loading on the piston against the cylinder wall.
With the induction in the front, that means the exhaust pipe must exit to the rear, and what a pipe it is. To gain tuned length, what Yamaha calls a "tornado style" pipe makes a twisting loop in the center of the frame. With no conventional airbox to deal with, the shock is angled forward and centered in the frame. As you can imagine, adjusting shock spring preload is a snap. Additionally, fuel is carried closer to the center of the chassis.
We haven't ridden the bike, but the ergonomics should be much like the YZ250F, which we have ridden, and the bike should be very easy for the rider to move around on front-to-back. For sure the YZ450F will have more visual "Wow!" than any bike at the track. We can't wait to see if it feels as good as it looks.

source: dirtrider.com
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