There is no question the 2018 Suzuki RM-Z250 is one of the best-handling machines in its class, but it’s also no secret that raw horsepower is not one of its strong points. All engine builders agree increasing engine performance on the RM-Z250 is possible but by no means easy or cheap, especially when playing by the rules. Luckily for us, rules don’t apply for this build.As we said before, the RM-Z250 does handle well, but, naturally, we weren’t satisfied with that and had to see if we could make it better. The unit comes off the showroom floor with a Kayaba PSF2 pneumatic spring front fork that uses air chambers in place of steel springs. This design features loads of adjustment but requires constant maintenance of air pressure and can be confusing.
The other major complaint is initial harshness in the stroke, especially on small chop. We turned to Paul Thede and his crew at Race Tech for some help. They have a full kit that turns the KYB PSF2 into a conventional single-spring fork setup that is similar to the Showa that came stock on the 2013–’16 RM-Z250 models or what is currently on the 2018 KX250F. This eliminates the use of air altogether. Race Tech removed damping and air on one side and replaced it with a spring. This meant Race Tech had to double the damping on the other side. The right side now has the spring, and the left now has the damping.
After the conversion was performed, compression was on the bottom of the right leg (only on the one damping leg). High- and low-speed rebound are on the top of the left leg—just like stock—but you only adjust one side. Race Tech also installed its Gold Valve to improve the initial plushness of the now SFF fork. The spring conversion kits can be purchased from Race Tech for around $900 or installed for about $1000. We recommend having a trained suspension technician handle the conversion. We also had Race Tech do some work on the shock. Race Tech changed the spring rate, added a Gold Valve and re-valved the shock internally for our specific application, but nothing as in-depth as what they did to the fork.
Suzuki-supported race teams like JGR will spend huge amounts of coin getting every last ounce of power from the engine legally, with head mods, crank balancing, valve jobs, ignitions and running race fuel. We didn’t do any of that! The rulebook doesn’t exist on this build, and the one almost surefire way to get more power is to go bigger, so that’s what we did. Cylinder Works makes a 3mm big-bore kit that includes the cylinder, forged Vertex piston and a top-end gasket kit from Cometic. This complete kit bolted right onto the OEM cases and head without any modifications.
Stage 2 Hot Cams were also installed. These cams are designed specifically for engines with modified and high-flow exhaust systems like the FMF 4.1 titanium we bolted on. The last major internal engine modification was a complete Hinson billetproof clutch with stiffer springs than stock for a more positive clutch engagement. A high-pressure CV4 radiator cap and silicone radiator hoses gave the cooling system a boost.
This build has a host of bolt-on items from companies like Works Connection, Motoseat, Motion Pro, Cycra, Supersprox, Uni Filter and Tusk Off-Road. They all either provide protection, enhance performance or just add to the overall bling factor, and it’s all topped off by a semi-custom graphics kit from Decal Works.
We learned two major lessons with this RM-Z build. First, it’s very difficult to make huge engine performance gains on the 2018 RM-Z250 no matter how much coin you have in the old bank account. All of the upgrades we made were with bolt-on items that could be easily removed. Mapping-wise, all we did was install the richer coupler that Suzuki provides with every machine.
The RM-Z270 has noticeable increases down low and in the mid-range, but nothing substantial on top. We do think more power can be gained with head porting and an ignition. Maybe that could be phase two down the road. When starting the RM-Z270, you must start at top dead center and kick all the way through; otherwise, you might have trouble getting it to fire.
Second, the RM-Z handles well, but there is always room for improvement. All the test riders agree that the Race Tech spring conversion has a plusher feel on small chop than the air fork and retains its good resistance to bottoming—although this particular Race Tech setup was a bit on the soft side for our larger or faster test riders. Eliminating the air pressure factor is a load off everyone’s mind, and we are pleased to see multiple manufacturers returning to spring-fork setups.
Overall, our RM-Z270 project was faster, handled better and certainly turned more heads than it did when it came off the assembly line.