I run mine closed with 10 disks, its loud as hell. The one problem with the stock warrior engine I noticed is the valve float at high rpm, the stock springs suck, since I did the engine mine pulls to the top real quick with no valve float. At the very least, and it was mentioned in Dirt Wheels buy a set of valve springs, there cheap and easy to put in. This will end that weird rev limiter sound you get when you rev it all the way up. Also when I ran the pipe with just the open cap on the back it felt like I lost torque, remember most engines do need some kind of back pressure to help with cylinder scavaging, this might explain the torque loss.
