Cycle News - Archive Issues - 1990's

underneath the rear portion of the fuel tank). The computer that controls the exhaust valve is also called the enginemanagement system. Among other duties, this computei reads sensors that are located allover the engine, some of which monitor engine speed, throttle opening, heat and so on. Via these sensors, the computer knows exactly what's going on inside the EXP-2'smotor, and if the computer doesn't like what it reads, it can make the necessary corrections to keep the motor operating at maximum efficiency, as well as keeping it from selfdestructing. For example, there's a heat sensor located in the bike's spark plug, and if the engine management computer detects any overheating readings from this sensor, as a result of extreme detonation caused by bad gas, heavy engine loads, or whatever, the computer will take matters into its own hands. At first, it might tell the computer that runs the fuel-injection system to start running richer, and if that doesn't work, the engine management can decide to shut the motor down completely before disaster strikes. At the Nevada Rally, Ogilvie once saw overheating warning lights come on and decided to kill the motor and coast for a while until the bike cooled off enough to be restarted. Perhaps the most interesting aspect of the EXP-2 motor is that it is designed to "diesel" at certain engine speeds. The spark plug actually only fires to aid starting and doesn't function again until the engine spins at 4000 rpm or faster. Evidently, Honda has discovered that detonation, or pre-detonation, which usually results in skin-crawling pinging (something YZ490 owners are all too familiar with), isn't necessarily a bad thing as long as H is con trolled. They found, after studying the phenomenon of auto run-on (when your car keeps running long after you turn off the igrution), that by controlling detonation, you can ultimately improve fuel economy and reduce emissions, producing usable horsepower all the while. Honda was able to accomplish this controlled detonation primarily because of the computers and incorporating fuel-injection. Ogilvie says that at race speeds, such as at the Baja 1000, the EXP-2 averaged between 23-25 miles per gallon, burning nothing more than everyday pump gas Chevron Supreme, to be exact. The CD igrution system on the EXP-2 ,is the same type as that used on Honda's production models, except for the aformentioned detonation sensor which is located in the spark plug. A small battery, just like that used on the XL250, shares space with the computers inside the "airbox." Evidently, the motor is very reliable. The bike has competed in the '95 ParisGranada Rally, the Nevada Rally and the Baja 1000 and has finished all of them, not to mention placed welL At ParisGranada, the EXP-2 finished fifth; at the Nevada Rally the bike took eighth; and at the Baja 1000, Chuck Miller, Paul Ostbo and Greg Bringle rode the bike to seventh overall. Not bad for singlecylinder, 400cc two-stroke. No expense was spared when it came to keeping the EXP-2light. The frame and the huge 4.2-gallon fuel tank are constructed of lightweight aluminum, the engine cases are made out of magnesium, and many parts are titanium, including the footpegs and just about every nut and bolt. Ogilvie says that in material alone, the EXP-2 is worth at least $500,000. Even with the exotic metals, the bike still weighs in at a hefty 282 pounds dry. Racing is a big part in the development of the EXP-2's powerplant, and that's why Honda went to great lengths a After our short ride on the bike, we can definitely see that Hpnda is on the right track toward building a very ridable two-stroke engine that is "friendly to Man and earth." Definitely encouraging, to say the least. So what's the next step? Honda says, "... to mature these new technologies, to study their application to future production models at reasonable cost." 0 (Left) The EXP-2 runs Incredibly clean. After having been ridden all day, there was very little exhaust residue In the bike's tailpipe. Despite being environmentally friendly, the EXP-2 roosts. to make the bike light and race-worthy. However, Honda says, "It (the bike) was not designed to win, but as a running laboratory of new technologies." Honda invited us to the California high desert near Barstow to ride the EXP-2, and we really didn't know what to expect from the motorcycle - after all, it is designed to meet emission standards through the year 2000. So, how much fun could it be to ride? Also, the bike had jUst been raced at the Baja 1000, and to demonstrate the sturdiness of the EXP-2, Honda chose not to prep the bike before we rode it. Starting the EXP-2 was pretty much like starting any big-bore two-stroke, except for having to ~ on the battery with a toggle switch located behind the front cowling before giving a healthy kick on the right-side kickstart lever. With just a touch of throttle, the EXP-2 "fires" to life, and right away you know that something is different about the bike. First of all, at near idle, the engine is extremely quiet.- there's very little exhaust noise, and you can detect telltale signs of detonation, but not the scary kind of detonation or pinging that you would come to expect from a poorly jetted two-stroke. Instead, the EXP-2's engine runs smoothly, despite the fact the spark plug isn't sparking. Running through the gears for the first time, we were simply amazed by how much bottom-end power and torque the EXP-2 has, and then were completely surprised to find an equal amount of power on top. The EXP-2 pulls and pulls and just keeps pulling - a lot harder than we had expected. Ogilvie says the EXP-2 has been clocked at approximately 105 mph, and we have no reason to doubt it. On one particular wide, long and super-smooth dirt road, th.e EXP-2 went as fast as I wanted to go and had plenty of power left over. Cruising along at about 60-70 mph, you can grab a handful of throttle and get the rear tire to break loose. You would think that a bike that could go 105 mph on the high-speed roads would be "bog city" on the twisties, or while "trials-ing it" over loose rocks and boulders. You would think that the clutch would fry up in a matt~ of minutes, but not with the EXP2. The bike is just as potent over the slow-speed stuff as it is on flat ground. It's through the leg-paddling sections, when the going gets slow, where the EXP-2 definitely feels different. The bike always feels as though the engine is running hot or is on the verge of running out of gas - you know, when there's that slight pinging from the top end and the engine takes longer to rev down. Normally in these situations, you'd be afraid to open up the throttle, afraid that the (Allow) To ImproIIe fuel economy . end reduce emissions, the EXP-2's motor Is -.ally d8sigi i8d to "dIe8eI" at low rpm. It aI80 produces good boltDITHllld, whlIe topping out at1OS~ (Right) The fuel Injectton (on top) and the computer (black box) that runa It. piston will disintegrate and break into a million pieces. But on the EXP-2· that feeling never really gets that far. Instead, you just roll on the throttle, any detectable detonation instantly goes away, and the bike responds immediately with a healthy dose of power, able to pull you out of any tight situation. The motor truly is amazing, and the power it puts out is remarkable. The EXP-2 has a powerband like no other single-cylinder, two-stroke engine we've ever ridden. From 1 mph to 100 mph, the bike continually pulls in a very docile manner, and there's no hard hit anywhere in the ultra-wide powerband. Basically, the EXP-2 pulls off the bottom like a four-stroke, but screams on top like a traditional two-stroke. The only thing we really didn't care for about the EXP-2's motor was the sound it emits. While the motor is very quiet, it produces a kind of raspy sound similar to many other choked-up singlecylinder, two-stroke off-road bikes on the market. It certainly doesn't have that hearty, deep tone produced by bikes like the CR250 or 500 MXers. And since the exhaust is so quiet, you can hear a lot of activity going on insid,e the engine cases. Despite having just competed at the Baja 1000, the EXP-2 did not feel like a bike that had been flogged for over 1100 miles straight. Instead, the bike felt snappy an? ran crisp and clean. Honda EXP-2 ERs\IM Slnje-cyliIll'ler,1lqdd coded ~ CWIAdIr IncIRe .•.........•... .35 dll\J8IS !lip' ." ant BIns CIrIIII.llan A02cc .ao x80llm .ElectilfIic FlAIl ~ ...................................CD1 1l~1I1 .5speed lIntFIIDI •....•..••.•••.........~ ............................... .13Q111l:1' ....................... _ • 7. . CllllllfDlr Fall ClIP. II ,.8. .Dltt Ia. A.2p. 33

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