PROJECT ATV: YAMAHA YFZ545
Recently, we caught up with JSR Performance out of Wichita, Kansas, which is a performance company built on racing heritage. John Stallworth, owner of JSR, knows what it takes to win races. He has won Pikes Peak on machines he has built a staggering seven times, and even more of his motors have won races up the famed Colorado climb. To say JSR knows how to make power is an understatement.
BIG PARTS, BIG POWER
Starting off with what is arguably this generation’s best sport ATV, JSR pushed the envelope to the max with this YFZ-R. Not content with 40-something horsepower in a 430-pound ATV, they pulled the entire motor apart and built it from the ground up. Starting with a billet stroker crank from Falicon, they increased the YFZ’s stroke from 63.4mm to 73.4mm. Then, a custom 3mm-plus, big-bore custom Wiseco piston was attached to the top of the rod with a taller stroker cylinder that JSR custom builds. Custom Web camshafts and 1-plus titanium Xceldyne valves round out the ported and polished five-valve head complete with stiffer valve springs.
The engine breathes in clean air through a Fuel Customs intake, which we reviewed on a YFZ a couple months back. JSR’s full-exhaust system with a large-core silencer handles the spent gasses. JSR even added a larger, 46mm throttle body and larger injector, with an Edge Controller by Performance Electronics handling a custom-tailored fuel and ignition map. The machine is tuned to run on E85 corn fuel, which comes out of the pump at around 105 octane and is much cheaper than race gas. A Wiseco clutch basket and inner hub mate up to a Slingshot lockup clutch from GP Engineering to put the insane power to the ground, as JSR couldn’t get a normal clutch to hold up to the abuse. Finally, JSR disassembled the transmission and micro polished all the parts to increase shifting smoothness and decrease wear on the gears and moving parts.
With the high-compression motor tuned to run on E85, the YFZ545 dynos at just over 70 rear-wheel horsepower, nearly double the stock output. A lower-compresion piston can be had to run with premium pump gas, dropping horsepower to around 64–65. The YFZ ran Pikes Peak last year, coming in fourth overall in the Open ATV class, marking John’s first run since a bad crash had him hospitalized shortly before. For both man and machine, that’s thoroughly impressive.
UNLEASH THE BEAST
We threw a leg over the white-and-red YFZ in Little Sahara, Oklahoma, during Sandfest. The weather was perfect, with a little rain to keep the sand damp for extra traction. After John tuned the YFZ from his laptop to cure a cold-start problem the YFZ had in the cold, damp air, the CV4 lithium battery spun the big motor to life in a hurry. It idles just like a stock motor, and once it was warmed up, we headed out for a test run.
Cracking the throttle for the first time will wake you up out of a dead slumber (it sounds like thunder clapping through the hills). Any trained ear can tell this is no ordinary YFZ, and the smell of the E85’s exhaust fumes, while not as sweet as race gas, had our nostrils perked up as well. Rolling through the first three gears slowly showed no signs of hiccuping or hesitation, as the JSR team spent a lot of time tuning the YFZ to run as smooth as stock. The first full-throttle third-gear pull we did across the flats in the sand had us hooked, as the YFZ stretches your arms in a hurry! Even with the big ITP paddles throwing buckets of sand behind the YFZ, it struggled to keep traction in the damp sand as we ran it through the gears. The motor hadn’t been rebuilt since the Pikes Peak race, but it felt like a brand-new engine with no abnormal noise, vibration or flat spots. This YFZ flat-out hauls, and it’s too much power for novice riders, we must say. The front end will claw for the sky in just about any gear at almost any speed, and the torque from the 545 engine is phenomenal. After traversing a few dunes into the trails of Little Sahara, we had left our riding buddies behind, so we stopped to see how well it idled after being ridden hard. To our surprise, it just calmly burbled at normal idle speed without any sputtering or odd stalling.
The E85 tune did get a little cranky once when we flooded the engine trying to start it, but the lithium battery kept cranking the motor until it fired back to life in a little spurt of white smoke from all the unburnt fuel. The stock shocks were valved and sprung by Race Tech and provided a smooth ride with great bottoming resistance, which really helped while airing out the YFZ in the dunes. It’s just as controllable as a stock YFZ, albeit unspeakably quicker when you whack the throttle open.
Unlike some big-bore or stroker motors we have tested, the JSR engine felt like a thoroughly engineered piece, with the hard-starting in cold weather being the only downfall. JSR is working on the tune to fix the issue, but it’s not something we couldn’t live with in exchange for all this awesome power. What surprised us is that this motor already had some hard hours on it, and even after the thorough thrashing we gave it, it never had an issue. No overheating, no blown head gaskets and no big blowups—just a ton of power, instantaneous throttle response and numerous ear-to-ear grins.
BITS & PIECES
Streamline Brakes outfitted the YFZ with a host of upgrades, including upgraded rotors and stainless braided brake lines to haul it down from speed with grace and style. CV4 heat shielding keeps the fuel cool, and their silicone radiator hoses add a custom look. The Edge tuner from Performance Electronics is a standalone ECU that allows adjustment of fuel, timing, boost pressure for turbo applications, and even a launch-control function. Performance Electronics has tuning applications for a host of machines, so check out their site at www.pe-ltd.com. It is by far the most in-depth tuning application we have used, and it allows you to adjust every controllable aspect of the engine.
Here’s the “ouch” part of the equation: to play in this realm, you need big bucks. The YFZ545R build you see here totalled to a whopping $6800—that includes every piece that’s on the machine, minus the cost of the original YFZ. If you want power but can’t pay that kind of coin, JSR has much more budget-oriented kits and options, so call them at (316) 269-4465 and ask for the Dirt Wheels discount. With stock bore and stroke, JSR can have you running at around 54–55 wheel horsepower, up from the stock YFZ’s 38–39. A big-bore kit hits about 60 horsepower, and a pump gas stroker motor makes around 65 with their full kit.
After riding the JSR YFZ, we are believers in big-horsepower, single-cylinder engines. We have tested some big builds—some good, some bad—and the JSR kit is one of the best. If you’ve got a need for speed and want to leave all your friends in a flurry of roost, call up JSR for the star treatment.
PARTS AND PRICE LIST:
JSR 98mm-tall stroker cylinder
JSR Wiseco’s custom piston
JSR exhaust system w/ big-core silencer
Falicon 10mm billet stroker crank
+1 Titanium Xceldyne valves
Webcams custom grind
Ferrea valve springs
JSR/Rage ported head
Wiseco clutch basket and inner hub
Slingshot lockup clutch from GP Engineering
Micropolished transmission and all rotating engine components
46mm throttle body with larger custom injector
Modded to run E-85
Fuel customs intake
The edge controller made by Performance Electronics w/ custom mapping
CV4 gas tank heat shield
CV4 radiator hoses
CV4 lithium battery
Streamline brake rotors and brake lines
Stock shocks built by Race Tech (front and rear)
Hyper wheels and ITP Dune Star tires