OK, here is the deal. I'm a NYSC Small Engine Tech and studied under AMI for Yamaha when I lived in Florida.

On a 2-Stroke and this includes Glow the less back pressure the better. It improves power and a bit louder... the only downside is fuel consumption is increased.

On a 4-Stroke it needs the proper back pressure to run properly. Without it it weakens the horsepower by 10-20 % and damages the valves after a while from unheated air hitting the hot exaust valves. Also the 4-stroke will run on the rich side and it takes a bit to get it somewhat lean without custom jetting.

Sure it sounds great but but in the end it damages the engine. If you want to go straight pipe, you have to change the Jetting in the Carb. If it's fuel injected the computer has to be manipulated or switched. If you don't believe me ask anyone who straight pipes a Harley Davidson, they usually pay for a Top End much sooner than someone who keeps the baffels in.

I like loud glow engines and I'm not a Harely Davidson fan. The best answer I can give is call the engine manufacture or get after market mufflers that are designed for your engine to help increase preformance and loudness.

Hope you got the answer you're looking for.