I find that they (SLP LMs) are not that loud on the highway at least inside the car...they are loudest on a cold startup and at mid to wide open throttle.

 

Everything stock, the SLPs sound really good. I sold my set to a guy who put them on his stock GT and it sounded incredible. That was months ago, and he still has them on there. Regardless of setup, the SLPs will be louder than any muffler. When I had my MAC mufflers, I really liked them a lot. They were just not a good combo with an offroad midpipe, they get raspy.

 

I just took mine off last night. I loved them with stock everything. I just put headers and a Catted H pipe on and they were really loud. The problem with them is the trumpeting that they produce in numerous RPM ranges. If they didn't do that I would have left them on. Back to factory for now.

 

The trumpeting does not get any better when you take the cats off!

 

I didn't notice trumpeting with Hiflo cats

 

no cats, no trumpets here. i order a prochamber w/ highflow cats, and intentionally gutted them using that cat chamber
as a resinator. this setup make the prochamber sound awesome, w/ imco extreme axleback. did'nt want to hack factory h.

 

I was referring to the SLPs, the trumpets with those are terrible without cats

 

+1 , i've also had slps on... when you are new to the inital sound, you think its great.but they are not a good sound for the mustang