Rearward slanting engine for 2010 YZ450F

Husaberg and BMW have the forward slanting engine, and now Yamaha has gone in the opposite direction with its all-new 2010 model YZ450F.

The long-awaited adoption of fuel injection, utilising a 12-hole injector, is the centrepiece of the new Yamaha, which allowed the marque's engineers to lock in a unique design philosophy:  a rearward slanting engine with a straight intake tract mounted in a lightweight bilateral beam frame.

The air cleaner is now located where the tank once was, so the intake tract can have a straight shot into the cylinder head. To achieve the proper exhaust pipe length from the rearward-slanting cylinder, the pipe twists in a coil before reaching the silencer.

In addition to the intake benefits, Yamaha also claims the rearward slanting engine centralises mass towards the centre of the machine, giving the "engineers more freedom in locating the rear suspension". Specifically, the mounting points for the rear suspension and swingarm can be moved forward towards the centre of the chassis.

Other claimed benefits of the forward-mounted intake include cooler intake air because it is unheated by the engine, and cleaner air, because the dirt and dust kicked up by the rear tyre is further away from the intake system.

The four-valve engine in EFI configuration now has  2mm bigger bore, and the stroke has been shortened by 2.6mm. Yamaha will offer a plug-in setting tool as an aftermarket item to adjust the fuel load and ignition map for different conditions.

The compression ratio is 12.5:1, compared to 12.3:1 on the existing model. The bike has a new forged aluminium piston, and it retains the titanium valves.

The YZ450F also has an offset cylinder, which is 12mm from the centre of the crankshaft. Yamaha reckons this reduces friction loss and "contributes to better engine characteristics". Just how that can be measured is the million dollar question.

Either way, it's the first time an offset cylinder has been adopted on a Yamaha production off-road competition model.

The aluminium frame on the YZ450F has been produced using die-cast technology, the same process that Ducati has used on its recent roadbike releases to shave vital kilograms and add strength. IT consists of 16 different components.

Supporting the frame is new suspension, with the shock absorber now positioned in line with the machine's central axis, and the spring has been moved about 30mm lower.

The shock cylinder diameter has been increased from 46 to 50mm, while the stroke on the forks is now 310mm, uprated form 300mm.

The handlebars remain four-way adjustable, there is now a flatter seat, and the fuel tank is now positioned under the seat.

Colours are blur or white, with price and availability still to be announced.

Other manufacturers to have already released details on their 2010 450cc motocross tackle include Kawasaki, KTM and Suzuki.