RE: Can you run a gas motor with no muffler?
Some intake charge may be lost without backpressure and no muffler. The spent exhaust charge may exit more quickly without a muffler though. My experience has been tons of noise but a small rpm increase with no muffler compared to a stock, non tuned muffler. I thought engines were great before they had mufflers or throttles..... but that's when my hearing started to go.
Running a 4-stroke without a muffler or header pipe I've heard can lead to a warped exhaust valve when cold air hits it right after a shut down.