the reason most folks run without a cover is to keep from blowing a belt. sure it keeps the clutches ambient temp rather than hold the heat.
what i tell everyone is...... why put a shit ton of blowers in the clutch cover to try and get the heat out to keep the belt cool, why not just make the clutches run cooler? the belt temp is purely because of the clutch calibrations. when you run a dune and the RPM bog down, its because the clutch is in too high of a gear ratio. your clutch is effectively in 4th gear and needs to downshift to 3rd gear. when the clutch is in too high of a gear ratio you bog down, AND you create belt heat.
when i am testing calibrations and especially on race machines i have a special belt that i use. i have holes drilled in it thru the center from top to bottom and side to side. small holes to fit a tiny thermocouple in so i can test the heat inside a belt. i use a laser gun to measure the outside belt temps as well. when the outsides of the belt is hot and the center is not, you have belt slip. when the outside and inside of the belt is the same temp, you dont have belt slip. its pretty simple.
on my test track i have a long uphill climb. its a super hard hill climb and we all call it killer hill. simply because it will kill a normal stock clutched car. for a perfect example i will give you this:
on this hill, its a fast 45mph straight away that has a hard left hander that is banked so you can take at speeds. this left hander is the beginning of a long uphill pull. the uphill pull is about 200-300ft and around 50 degrees. its a big pull. a bone stock xp1000 will bog down and loose around 1000-1300RPM on this hill. the reason is when you come down that straight away you are gaining gear ratio as the clutch upshifts. around 45mph the clutch will be near its maximim ratio (5th gear) and you hit this super fast banked turn and start climbing this huge hill. since you dont let off the throttle, you are entering and exiting this turn in 5th gear, and since the stock clutch is inadequately calibrated to backshift the clutch under full throttle, you end up bogging all the way up the hill as the clutch is stuck in 5th gear. as an XP1000 climbs this hill and bogs 1000RPM the belt temp will climb in that 10 second time over 75 degrees. not because the belt is slipping, but because the belt is under too much load from being in the wrong gear ratio. the whole belt thru and thru will spike from 225 degrees to as high as 315 i have seen before in that one uphill pull.
on that uphill pull i have been able to determine about how the belt will increase in temp as you bog down.
300RPM bog will give you around 25 or so degrees on that 10-15 second pull
500RPM bog will give you over 40 degrees.
1000RPM will spike as high as 75 degrees.
so what happens is when you are blasting the dunes at glamis or wherever rolling the bowls having a good ole time your belt temps are well over 225 and every time you pull another big dune and the RPM bog down you are creating belt heat. when you create belt heat from the clutch being in the wrong gear ratio you shorten the belt life. the belts dont like heat. there is no way around it. eventually it will blow. so folks taking the cover off are trying to make the clutches run cooler is a bandaid and not a real fix for the problem. the real fix for the problem is to fix the thing that causes the heat. you can make the clutch work efficiently and perfectly with different calibrations, or replacing the clutch with ones that are more efficient. on my test track which is set up like a GNCC cross country course thru the woods, i have some amazing hill climbs, jumps, banked corners and all together to make one of the fastest woods courses you can find. on my course a stock XP1000 will make about 3 laps before it blows a belt. i watched a guy on a maverick melt the belt in less than 2 laps. the hills i have will bog a machine down and kill a belt. the way i built this course allows me to accurately test a machine in some of the hardest possible situations known. after i am done with the clutches you can run for an hour straight and the belt temps never get above 195. as a matter of fact the lap record here right now is held by a pro trophy truck driver who brought his XP1000 here because he couldnt keep it from blowing belts. after a day here he not only set the lap record, but ran for a solid hour moto to simulate the cross country race series he races that have hour long races. we timed him and after the hour he ran, his belt temp was 195. the absolute fastest person to ever come here he ran 5 second faster lap time than anyone, and his belt temps were better than any of you can even get out of your cars with stock clutches, on a sunday cruise. on a normal rider, someone who comes and can be fast here, but is still quite a few seconds slower than the lap record, typically their belt temps after 10 laps is about 145-170 degrees. pulling the hills and muscling up the hills and jumping out the top of the hills rather than bogging down and struggling to make it up them will keep the belt temps smooth and cool and consistent. my track is about a mile long, takes about 1:40 on a stock XP1000. we have drivers come and spend the morning getting used to their machine, make 10-20 laps to learn the course and then try and set a fast lap to record a before time. doing the clutch calibrations we do, we consistently see 6-8 seconds a lap faster times after the work is done. plus belt temps drop over 100 degrees.
the same goes for sand. bogging up olds means you arent in the powerband, losing wheel speed cause the clutch is in too high of a gear ratio, and creating excessive belt temps. fix the reason the clutch gets hot, drop the belt temps with proper calibrations rather than pull the cover off and have a clutch that wears out in 250 miles of sand.
the reason Biff doesnt run a cover is beacuse they cant keep a belt on them if they run a cover. they order their clutches straight from STM and install them. i am sure STM helped them over the phone to get the calibrations close but i feel certain there is still plenty left on the table as far as power and reliability with those machines from having the clutch properly dialed in. i went out with the factory arctic cat cross country team testing once at stoney lonesome part. Greg had rented the park for testing for a week. i went and worked on one of the factory arctic cat wildcats and did my clutch work to it. gregs guys were there testing Donnie Coffeys wildcat build, the radical lime green one that was built for cross country racing. they were running Gregs carbon fiber cover and had two huge Nascar brake duct blowers blowing in it to keep the clutch cool. his machine i believe had 160whp at the time, and they were still having belt problems. i havent seen Donnie run that machine since that day two years ago. although they are STUPID fast in the dunes. i am sure there is no cover to try and help save the belt.
