I have SLPs on mine. Yes they are louder than stock, but quieter than most other pipes, including SLP's mtn max pipes.
They work best at 8800-8900 rpms on my sled. The SLP jetting chart is very close. I'd start with their jetting specs first, then check your plugs, you might be able to go down one size, and maybe 1/2 position on the needle clip. The SLP jetting chart does skip some sizes ie; 152 to 150. You can buy the in between sizes from Yamaha, ie; 151.3s although they are more money.
They're clutching chart was off for me. Mine is a 02 Viper that I put a 136" track on, and ride the mountains. I found that the pipes just didn't like the 8Ek weights at higher elevations (4000'-7000'), they work fine down low. It would under-rev on the bottom end and over-rev on the top. I switched to 8CRs and instantly got a straight shift. Your Mtn Viper I believe comes with 8DN-10s. They have a force curve that is similiar to 8CRs and should work fine.
I do a wide range of riding, trail, boondocking, climbing and drag racing. The SLPs are working well for me, fuel mileage is pretty good as long as you dont ride all day long with it pinned to the bar!
