Don't know if Slimlines have changed in the last 5-8 years, but I know for a fact that the first ones were LOUD. I pulled out an OS.50 that was still new in the box to use on an ARF. Had a Slimline I'd bought with the engine. Both were purchased some years back, more than 15. I took the sucker out to the field and setup a breakin rig beyond the pits. Figured I'd get an hour or two running during the day's flying. WRONG.....

It was on a day all the retired guys hang out. We bring sandwiches and fly all day. First time I cranked that sucker up nobody could hear what anybody else was saying. OK, a number of the old boys don't hear too good to begin with, but for the same reason, most of they talk real loud to begin with. Dang the sucker was loud. It actually hurt your ears up close. Everybody was amazed. One guy did remember trying to use a slimline pitts years and years before and having to swap it out.

So old ones are different.

Right now I use a couple of Bissons and a couple of Slimlines. They're all on OS91s and all sound about the same. And would be described as mufflers that're definitely quiet. I've gotten a Q recently but not got it scheduled to go into anything yet. Maybe will retrofit it to see how it does. Sometimes mfg's improve stuff (like power) when they're upgrading, even when the purpose is different.