I had always been under the impression that backpressure was vital to engines, especially mildy tuned ones. In fact, all the data i have ever read suggests it is required at least on car engines and proven to add power in dyno tests. That is on car engines. This is certainly not a car engine. Why then, when my muffler (a hollow one at that) blew off at the head pipe on my HT motor during a ride, did the bike take off like a rocket? Well, you know what I mean. Talk about poor welding/inferior metal. Substantial power gain with NO backpressure . I dont get it. All of a sudden the bike picked up a few MPH or so and got louder, although it wasnt too much louder than the hollow muffler. Actually it took me about 15 seconds of riding before I noticed it was gone, no BS. It seems like I read a similar thread a while back but I cant find it now. Does anyone have a plausible explanation for this, because I am at a loss.