Silencers are totally unnecessary for power production. "Back in the Day", no four stroke race bike ever had one. Having said that, a lot has been learned since 1975. And I'm not talking about suspension. Did you know that a stone stock '04 YZ250F Makes more horsepower than all but one of the 250 2 strokes in the '85 Dirt Rider 250 shootout? Designers like Doug Dubach and others have found innovative ways of pulling power out of modern four strokes and keeping the noise down at the same time. Lower noise levels reduce rider fatigue, and better silencer designs mean you don't have be loud to sound good, either. So, which do you want, loud, or powerful? I can send you proper dimensions for a megaphone that any shop student could roll up for you and would be THUNDEROUS on a 426, but it very well might not make as much power as a Dr.D or an FMF T4.