2001 arctic cat zr 800

Arctic Cat engine guru Greg Spaulding must have put a small amount of gamma radiation in the Arctic Power Valve (APV) housings of the ZR 800 engine. You know, the stuff that turned Bruce Banner into the big green Incredible Hulk when he crossed that stress threshold. When the new 800 twin crosses its own rpm threshold, it turns into a raging green monster.

We got the initial pilot run of the hot, new 785cc Suzuki twin to put on our dyno bench. What we found was downright amazing. But first, let's look at how the engine works.

"Our dealers weren't interested in an engine that was going to shake, rattle and roll," said Cat's Sled Manager, Joey Hallstrom at the introduction. "We've worked hard at making it smooth and quiet. Also, it is very good on fuel."

The solution to all of those concerns seems to have been the APV system. The flat slide valve is operated by a small servo motor that slams opens at exactly 6950 rpm and closes when the engine speed falls down to 6850 rpm. "We opted to use a servo system so that the valves always operate at specific engine speeds," explained Spaulding.

"No matter what elevation the sled is at, it will always want the same thing at the same time." Competitive models that use air pressure to actuate their valves will open and close at different rpm, depending on ambient conditions.

An added bonus the APV system paid Arctic Cat is reduced sound emissions. The sled runs noticeably quieter when the valves are closed.

Of course, once they open up, every pony in the engine joins the chorus. But it is acceptable.

The final plus for the new engine is its fuel economy. When you have more horsepower than a 600 at only 6400 rpm, you're not going to have to open up the throttle too far to maintain sensible trail speeds.
You want to know how it performed don't you? Fine. 141.1 horsepower at 7400 rpm. 102.1 foot/pounds of torque at 7200 rpm. Happy? We were.

When you look at the power curve for the 800 APV engine, you'll notice that right about 6950 is where the valves pop open, shining that gamma radiation onto the Hulkster. At 6900 rpm, the engine is pleading "don't make me angry, you wouldn't like me if I'm angry!" Hell, for that 20 horsepower infusion, we'd make the boss' wife angry.

Let's look at the torque. There's a 400 rpm band where it's over 100 pounds! All our Dynoman, Rich Daly from Dynoport, said about the results was "Torque monster." We'd agree, and its name shall be "Hulk."