Well I assume you are talking about the standard 2000 Z 440...that was a bummer year for the Z 440. Arctic Cat discontinued its Jag 340 and 440 after the 1999 model year and replaced them with the Z 440 and the new 370 in the value/family trail segment in 2000. Unfortionately in this process, the Z 440 lost its hydrolic brake and one of its carburators and ALOT of horsepower compared to the 99 and older models. The first thing you want to do is to restore the second carb, that should up the HP right there.
There isnt anything in the way for pipes that I know of for this model (or any fan cooled really) but I agree with the HeartThrob clutch kit. Maybe a nice 1" or so track on it too, you dont want too big of a lug track on a lower-hp fan model such as yours.
If you are talking about the 2000 Z440Sno-Pro, well the performance is much higher from the get go then the std model, but Cat upgraded the '01s with a new head, ignition, and pipe and that boosted HP significantly. Maybe you could search for the upgraded parts and see if you could obtain them for a decent price. I think those changes boosted the 01 up to about 66 HP stock.
