KTM readying for big 2011 year release of 350, linkage and fuel-injection
By Trevor Hedge
KTM are readying for the big 2011 year release of the 350 SX-F. KTM factory riders are already proving the might of the 350 over the established 450cc competition with Tony Cairoli looking set to run away with the World Motocross Championship. The performance of Cairoli certainly suggests that KTM’s new direction might indeed be the way of the future.
The 350 SX-F will certainly be the most eagerly awaited star of the show but the whole six model SX line-up of motocross machinery is much revamped for the new model year. The four-strokes however are much more revolutionary than the more mildly tweaked two-stroke line-up.
The DOCH 350 SX-F mill is fed by a Keihin 42mm throttle body with the convenience of an optional power map switch to easily change EFI characteristics at the flick of a switch. The 250 SX-F also benefits from the move to fuel injection but the big-bore 450 SX-F retains a Keihin 41mm FCR carburettor. The less focused EXC Enduro range of bikes will also not benefit from the change to EFI. The injected 250 and 350 SX-F carry a fuel pump inside their 7.5 litre fuel cells.
The 350 utilises an 88mm bore and 57.5mm stroke to achieve its 349.5cc capacity. Those dimensions provide a 13,000rpm capability and at 57.5mm the stroke is only marginally larger than the 54.8mm stroke of the 250 SX-F.
The 350 engine is lubricated by two oil pumps. Similar to the 250 SX-F system a pressure pump feeds the crank, piston, valve-train, clutch and ignition while a suction pump then extracts the oil from the bottom of the crankcase to feed the gearbox.
The 350 and 450 SX-F models both score electric start as standard with optional kick back-up while the 250 SX-F takes the opposite tack and ships only with a kick-starter with an electric start kit able to be retrofitted by a KTM dealer on request at an additional charge.
All motocross models, both four and two-stroke, both PDS and conventional linkage do benefit from completely new frames. The Austrian brand however is still shying away from the move to an alloy frame in favour retaining chro-moly tubes and spars to form the backbone of their motocross machines. KTM claim their frame is lighter and is easier to maintain. The Japanese brands tend to think the opposite.
KTM do seem to have changed their mind on their other long standing point of difference with the established class peerage. KTM have long been a stalwart proponent of the non-linkage rear end with the shock instead mounted directly on the swingarm. In KTM guise this system has always been referred to as PDS (Progressive Damping System). For 2011 KTM have finally relented and fitted a conventional linkage rear end to all four-stroke SX models. The two-stroke machines retain the previous PDS layout, as do the EXC range of Enduro machines.
KTM claim that the linear spring progression of the PDS is still beneficial to the lighter two-stroke machines while the more aggressive spring progression of the linkage system benefits the four-strokes, particularly in the extremes of Supercross and Motocross competition. For Enduro and Trail riding KTM believes the PDS still offers some advantages and thus the system is retained on the popular EXC range of Enduro machines. The retention of the PDS and the lack of EFI on the EXC machines will be sure to disappoint some customers.
A new aluminium swingarm has been designed to accommodate the linkage bikes while the PDS bikes also score a new swingarm due to the 2011 incarnation of the system sporting a longer shock to help improve rising rate characteristics. Both types of shock score KTM’s previously optional screw-cammed preload collar to simplify preload adjustment.
Up front the entire motocross range scores the latest generation 48mm inverted forks which boast new settings and fine tuning. WP will still manufacture all the KTM suspension components.
A myriad of other small changes from quieter mufflers to zinc-nickel coated spokes and strengthened clutches all help to improve the overall engineering of the breed.
KTM Australia is expecting to have the 2011 SX and SX-F range available from dealers as early as next month. KTM are eager to show their new mounts to the public and will run come and try days across the country where interested buyers will have a chance to sample the Austrian company’s latest wares.
KTM’s ‘Dirt Days’ campaign kicks off at Monza Park in Ballarat (VIC) on June 20 before heading to Murray Bridge (SA) on June 26. On July 3 the travelling road-show visits Conondale (QLD) on July 3 and heads to Sydney’s famous Appin circuit on July 25. WA is last cab off the rank with Byford’s Tumbulgum Park natural terrain layout offered for testing on August 1.
Pictorial – SX and SX-F Images
Pictorial – EXC Images