Whether you are riding dirt bikes for summer fun, for winter fitness prep or building a snowbike setup, we've found a winning recipe for getting 2-stroke dirt bikes as close to their EFI conterparts as possible.
We love a good FI four-stroke 450 for a snowbike, but that's not our first choice for summer singletrack. Everyone's entitled to their opinion, and we respect anyone who is out riding bikes. But our personal opinion is that modern 450cc dirt bikes are built to race, and that makes them difficult to turn into a singletrack machine with a big sweet spot. However, they definitely have the advantage when it comes to performing well at altitude.
Our favorite bikes are the tried-and-true 300cc two-stroke machines such as KTM 300 XC or XC-W, Husqvarna TE300 or TX 300, Beta RR 300 or Gas Gas XC300. These bikes have a nimble feel, broad powerband, strong bottom-end and are very hard to stall on technical trails.
But, they lose power as they gain altitude. To combat that, we run an RK Tek high-compression billet head on our 2017 KTM 300 XC-W and 2017 Husqvarna TE300 test bikes. We also added Lectron HV Mule carburetors and FMF Factory Fatty pipes. That trio of performance upgrades is what we consider the ultimate for altitude-compensation and maximum performance at high elevations.
But of those components, we feel that the RK Tek head is the first part that we'd add if we were staying on a budget, or recommending a place to start for other riders who want more out of their carbureted two-strokes.
The RK Tek head is a two-piece system with a water jacket and a dome that are both machined out of billet aluminum. What seems to make the difference in how this head performs compared to just milling the stock head is the patented dome shape that RK Tek designed. Milling the head works, but it's just not as good as running a dome like this.
On our two bikes, we saw a broader low-end pwoerband and more power at peak RPM at our normal riding areas that start at 5,000-feet elevation.
But where the heads really shined was when we hit the big mountains, unloading at 7,000 feet and getting up above 10,000 feet. The bikes seriously perform the same at that high altitude as they do down around 5,000 feet.
Last season, we ran a 300 all summer without changing the head out. That bike with the stock head would choke out and lose significant power at those high elevations around 9,000 and 10,000 feet. Running the 300s this year with RK Tek heads is a completely different experience as far as power is concerned.
RK Tek also touts improved cooling with its billet heads, plus improved fuel economy.
Heads are available anodized in orange, gold or black. Retail price is $325. Installation is fairly easy if you're mechanically apt. You just need to remove the fuel tank, drain the coolant, remove the stock head (we re-used the original o-ring from the stock head since our bikes were new, but RK Tek recommends installing with a new o-ring), install the RK Tek head and water jacket using the cylinder alignment pins to make sure it's positioned right, torque the head bolts to spek and replace the coolant.
More info: http://www.2strokeheads.com/KTMPERFORMANCE.htm