The best way to go smaller is to think oversize
JULY 2014 / DIRT BIKE 37
Pete Murray is the perfect guy for a 250F with a big-bore kit.
The Senior class is 270 heaven.
A lesson from history: you don’t have to be that old to remember the 500 two- stroke. It was condemned by its own success. It became so powerful that
few riders could handle it, and fewer still wanted to handle it.
The 450 four-stroke isn’t there yet. We’ve seen it evolve in a more even-handed
way, with the chassis and suspension keeping pace with the power. But, there’s
a distinct anti-450 underground. You can see it in the popularity of the KTM 350s
and 250Fs appearing in Vet and Senior classes. Older riders in particular are
downsizing in a big way and still racing head to head with 450s. On some tracks,
slower bikes are quicker. So if you’re one of the rebels, how do you do it? As
much as we love the KTM 350, it still weighs as much as a 450, and a 250F gives
up so much on the starts, hills and straights.
THE OVERSIZE ANSWER
Not surprisingly, the best way to downsize from a 450 is to upsize a 250. That’s
why over-bore kits are so popular. They’re common in Vet classes where displacement isn’t a controlled substance, and even more popular in the 250 class,
where it is. For this project we started with our Suzuki RM-Z250 for one simple
reason: It didn’t win our 250 shootout. You need to understand how odd that is.
It won that shootout for the previous two years running with almost no changes.
This time around it was beat out by both the Yamaha and the Kawasaki for one
reason and one reason only—it was outpowered.
Our knee-jerk reaction with most projects is to make a multi-purpose racer that
can handle motocross, as well as fast off-road races like the WORCS and Big Six
races. That idea was derailed by the scarcity of aftermarket parts for the Suzuki.
For reasons we don’t quite understand, RM-Z numbers have always been low.
RM-Zs simply don’t sell well, and it has nothing to do with the bike itself. It might
be consumer financing, a street-oriented dealer network, an absence of advertising or a curse from an old gypsy woman—we can’t say. The bottom line is that
we couldn’t find an oversized fuel tank, and that limits the bike to motocross and
short trail rides. This bike is a Senior-class flier, made for 80 percent moto, 20
percent whatever. Casey Huntley at MXDreamBikes was the foreman for the project, with Jay Clark and Pete Murray getting in on the action as well.
Step one was the big-bore kit itself. The Cylinder Works 270 kit for the Suzuki
includes a new barrel, piston, rings and gaskets for $680. This isn’t the first time
we’ve been down this road, so we knew what to expect. Adding displacement to
a 250F can prompt the following four results: