2001 cats zr 600 apv

OK, we'll admit it. We were surprised with the results of this month's dyno test. We had the pleasure of riding an early release version of the new ZR 600 with Cat's Arctic Power Valves modifying the exhaust port timing. When we rode it, it felt solid, strong and smooth. It felt as if it pulled harder than the 2000 ZR 600 EFI we had without the valves.

Just like with the ZR 800 engine, the APV system on the new 600 Suzuki twin is credited with boosting midrange and low end grunt as well as muffling engine sound and improving fuel efficiency. All of which it does. Our preview unit last winter was so quiet we could hear our 2000 Cat on the trail from the cockpit. Our sled used its gas much more frugally, boasting upwards of 13 miles per gallon. And it felt tough out of the hole.

But this new mill was also supposed to be a little stronger on the big end than its predecessor. Our run on the dyno bench of truth put an end to that rumor. Our best run on the 2001 600 APV twin achieved 105.7 horsepower with 67.8 foot pounds of torque. Last year, we tested a 2000 600 twin, without the valves, at 105.4 ponies with 67.3 pounds of torque. Not much of a difference. At least not enough that an untrained test pilot could appreciate. But why does it feel so much stronger? The answer is in the valves.

Cat has the APV's guillotine valves hooked up to a servo motor that automatically opens and shuts them at the prescribed engine speed. When the engine is spinning at 7100 rpm, it's cranking out 53 pounds of torque and 72 ponies. A mere 100 rpm later, the valves have popped open and the output leaps up to 60 pounds and 82 horsepower. If you're not ready for that kind of wallop, you could find yourself a bit surprised. It feels like the turbo kicks in and you're off and running.

The other benefit of the valves is that they broaden out the curves. On the 2000 version the torque curve peaks out in a 200 rpm band. On the 2001 engine, the torque stays above 67 pounds for a 400 rpm window. That makes it very tuner-friendly when you're trying to adjust the clutching.

This motor is moderately sensitive to jetting. In the course of our test session, Dynoport's Rich Daly noted that he tried many different setups before he hit the best run. "One jet size either way of our best run showed about a half of a horse," he said. "It shouldn't be too affected by changes in conditions over the course of a day."