Making the rocket more palatable
FMF• F2 Racing• Dicks Racing
By Tom Webb
If there’s an issue with the new KTM 450XC it’s that it is simply too much bike. The sucker is supposed to be an off-road bike and it snarls, explodes and claws for traction with more bite than a motocrosser. I live for the off-road world of desert riding, exploring, hill climbing and speed and yet the 450XC has me wide-eyed and screeching for control. So I came up with a plan, maintain the killer instinct of the machine, but give it some manners during roll-on.
LIVING WITH THE BEAST
First off, I use Dicks Racing suspension. I actually stole the fork and shock right off of our 24-Hour race machine and have found that it feels stiffer, is actually plusher and lets me hit both the motocross track and the off-road world without changing a clicker. This stuff is flat excellent.
Here’s what was done and why: The shock was revalved so that it was plusher on square edges and rocks, yet would not blow through the stroke. The rebound valving was matched to a stiffer 7.4 spring. Dicks Racing had tested progressively wound springs and felt that they got better versatility in the dampers ability to retain tractability, bottoming resistance and good cush for the off-roader with the straight rate coil. When done, the rear of the bike stays higher in the stroke, is plusher in the hack and chop, gobbled the whoops, stayed planted, and doesn’t want to kick.
The fork has Dicks Racing machined pistons that flow more oil. Not just bigger holes, actually smaller, but more of them. These pistons also have a free bleed feature built in for added plushness. After a few different valving combos, the compression side of the equation was solved. The rebound valving was stiffened slightly for more control, and the mid valves were altered to provide smoother action. Spring pre-load was reduced, the bladders were recharged, and the proper amount of oil was installed.
Here’s what we’ve learned, changed and tested over the last two months.
• We knew it was a rocket on top, which was actually true. One day while we were testing the world’s fastest dirt bike, we strapped a GPS on it and went 98.5 miles an hour with stock gearing.
• One of the first things we noticed when we got the bike was that it didn’t want to roll very well. It ended up being mostly the chain. We replaced it with a D.I.D. 520VT T-ring chain that let the machine roll much easier than the stock one.
• Second on the list came when we rode the XC at elevation. At 7000 ft and above it ran stuttery and nasty off the idle. We got with the F2 Racing Boys and they dug into the carburetion trying to find a setup that made the machine breath cleaner over a wider span terrain heights. After doing a plug check they found a problem with the spark plug itself. First of all the ground and center electrodes were bent. Second, the stock spark plug was designed for longevity, not performance. This plug had dual ground electrodes and a fat center electrode. This is designed to go 100,000 miles in your truck, not stellar performance for you bike. F2 fit in the correct plug that was designed for performance, and just the installation of the plug made the bike much better on the bottom. Throttle response was cleaner and crisper right from zero throttle all the way up.
• Finally F2’s new exhaust outlet, known as “Scram” was installed. This is the exhaust outlet that is bolted to the cylinder head and that the header pipe fits onto. The “Scram” has a different internal shape, which really brings bottom end power and response out of the engine. It doesn’t hurt top end at all and while change is subtle, it truly makes for better bottom, especially when you start climbing up in elevation.
• Webb got with FMF Racing and had them build him an exhaust with more header pipe length since he needed the smoother out of the hole snap. Their Power Bomb system proved to be incredible and mated wonderfully to the F2 Powerback kit. Suddenly the machine was more tractable, stalled less and still has a gnarly wallop that’ll peel your eyeballs into watery orbs.
THE CURTAIN CALL