Archive for January, 2011

Crazy Finns

Wednesday, January 19th, 2011

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Slavens 2011 KTM 350 XCF Goat

Thursday, January 6th, 2011

Forward: I called my dealer, Elite Motorsports, in 2009 and asked to be on the list for the upcoming 350. I received the bike in the late summer of 2010 and have been testing and building it ever since for a magazine test with Dirt Bike magazine. The bike is currently in California being tested. The magazine should hit the stands in February or March.

I picked up the 350 SXF for testing to learn about the new rear linkage suspension and to determine if the engine could be made trail worthy, not for high speed pussy trails but for Colorado’s nastiest rocky, rooty, switchback trails. After initial testing of the stock motocrosser I thought that I had made a big mistake. I’m not a fan of conversions, especially since KTM makes a model for every discipline imaginable, and the extremely harsh suspension and soft low-end power had me concerned.

To make it more enjoyable for engine testing, I attacked the suspension first. Since the forks are virtually the same as last year’s SXF models I already had developed some great settings, but instead I decided to wipe the slate clean and look at the fork set-up with a new set of eyes. I was happy with what I had developed for last year’s bikes but it can always be better. Resting on past accomplishments is never a good idea. I’m always trying to soften/improve harshness and deflection yet gain overall firmness that improves steering, stability, bottoming resistance, and improves the overall precision of the chassis. Also at the top of my wish list is a suspension that helps the rider when he makes a mistake, like hitting a wash-out at high speed that he didn’t see or hitting a root hidden by a shadow at a bad angle. Good suspension should make up for small pilot errors, not exacerbate the mistakes that we all make. When discussing the testing of the 350 fuel injection, Dave Simon commented ” I was hitting shit (with the Slavens Suspension), that normally gave me white knuckles, like it wasn’t even there. I  kind of forgot about the suspension and just rode and didn’t want to stop. It was the most fun I’ve had on a bike in a long time, maybe ever”.

Like most forks used for rocky rooty conditions, they just don’t flow fluid quick enough to respond to sharp square edged hits. This slow response gives that harsh, deflective, hacky feedback that makes us puss out and turn the throttle in the wrong direction. Addressing those issues is always my number one concern on all off-road forks and the WP closed chamber bladder forks have an additional issue that needs attention. Because of unwanted fluid migration from the outer chamber to the inner chamber, hydraulic pressure builds in the inner chamber and makes the fork become stiffer as you ride. The inner chamber has a check valve to release the pressure but as pressure builds in the outer chamber it overrides the pressure relief valve and the harshness increases. I developed a series of machining processes that greatly reduce the pressure called the Pressure Balance System (PBS). I combined the PBS with my high flow Next Level compression pistons that we design in house that are machined with a CNC water-jet machine to get the ports shaped for maximum flow. The mid-valve compression and rebound shim stacks and pistons along with the base valve compression stacks are all modified to increase performance and stability and spring rates are adjusted to match the rider weight. Other details; Italian made SKF seals are installed to reduce stiction and increase service life, Shock Sox are installed to increase seal life, the cartridge fluid is vacuum bled to remove excess oil gas (air) and the bladder pressure is increased to improve sealing to reduce oil migration. The final detail is installing STR Speed Bleeders and Clean Speed aluminum compression adjusters because the stock plastic adjusters crack and fail. The end result is a fork that stays up in the travel, has a firm and precise feel yet plush enough to track straight through gnarly rocks and roots.

The shock is much easier to correct than the forks. The new linkage system gives the shock the ability to handle a wider variety of terrain whereas the linkless PDS system is more sensitive about set-up and is more job specific. When correctly re-valved the linkage system soaks up square edge hits that would cause a PDS shock to kick. I make major changes to the dual compression control adjuster to alleviate harshness, add low speed valving to the compression shim stack to increase bottoming resistance and prevent wallowing , lighten up the high speed compression to make it more responsive to rocks and roots, reshape the rebound valving stack to increase overall stability and make the shock slightly more responsive to increase traction. A big mistake that most professional and home tuners make is bleeding the oil gas from the system by hand. A correctly valved and assembled shock will perform poorly if the fluid is aerated. The only way to properly bleed the system is with a WP vacuum bleeding machine. We have one of the few in this country and have been using it with great results for a long time. The final touch is a spring thrust bearing and high quality Slavens spring that is made in Holland and has correct dimensions that allow full shock travel. Many U.S tuners are using aftermarket springs that are designed for Japanese shocks and the springs will coil bind before reaching full travel.

The engine was my primary concern and very few performance parts are available. First I geared it down 1 tooth on the countershaft (13T) because first gear was way too tall for goat trails and the factory riders use a 13 for their GNCC mounts. Next I bolted on a FMF MegaBomb and Q4 to quiet the bike and give a mild boost to the low-end grunt. In Colorado spark arrestors are required and as of July 1, 2010 we have a new sound law and ALL off-road bikes must be 96db or less using the SAE J1287 testing method. The FMF system helped but I still wanted a lot more bottom-end pull.

Most of my trail riding is from 7000’ – 12,000’ and the thin high mountain air kills the power, especially the low-end. I called Dave “The Bitch” Simon at Simon Smart Body and he asked me to bring the bike to Phoenix so that he could develop a Smart Body for the 350. Dave builds bitchin billet machined throttle bodies that utilize a carburetor slide that flows much better than the stock cast body with the restrictive butterfly valve design like used on lawn mowers. He makes the bore diameter slightly smaller and that combined with the less restrictive slide and his own unique bore shape, the turbulence is greatly reduced and the velocity is dramatically improved. The end result is a huge boost from bottom to top. It’s a monster motor now that will out goat a mountain goat.

Dave also combines his Smart Body with a custom programmed Bazzaz FI tuner that is set up to match his throttle body. It is an extensive wiring harness and electronic box that piggybacks on to the stock Electronic Control Unit (ECU) and has a port to connect it via a USB cable to a computer. From there you can easily tweak the fuel injection for different elevations, air temperatures, mufflers, etc. When connected to a computer the included software provides an excellent format with fuel information for variable throttle settings and rpm levels. The multitude of grid fields can be changed individually or in groups. It sounds difficult but even a caveman could do it.

OTHER GOODIES
Wheels/tires:
• TUbliss system to improve traction, reduce weight, improve handling and eliminate pinch flats
• 18” rear rim from a ’11 XC was laced for additional tire choices
• Dunlop MX71 up front. Chosen for versatility. Pressure = 12lbs
• Mitas radial trials 400-18. I consider the Dunlop 803 the top performer but the Mitas is a close 2nd and last longer, won’t chunk on pavement sections, and has a more durable carcass that is more
resistant to cuts and has much less flex on high speed sections. Pressure = 6lbs
• Slime

Controls:
• Scotts top mount damper
• Flexx 10 degree enduro handlebars with Cycra handguards, BRP handguard mounts, Rigid bar end mounts , and Renthal Kevlar grips
• Prototype Pivot Pegz – they have stiffer springs that will soon be available to the public.

Other:
• KTM Hard Parts Tall gel seat
• Renthal o-ring chain
• Turntech 5amp battery – spins the engine quicker and reduces weight by 3lbs.
• Bullet Proof Designs – rear disc guard and radiator guards (the absolute best)
• Flatland skid plate – great protection, fair price
• PG GRIPZ graphics – very durable and look good
• BRP chain guide – more durable and longer service life
• STR rear brake pedal plate and rear brake caliper cooler (a must for brake draggers)

FYI: Everything on this bike is available at Slavens Racing.com

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