I have a 91 5.0 LX Hatch with an AOD. It has BBK shorties, catco h-pipe (with cats) and a MAC catback. It drones something awful at 2K RPM. I have to replace the mid-pipe, which off road mid-pipe will reduce the drone.
H-pipe/x-pipe, any particular brand?
with an O/R h-pipe/X-pipe it would probably just get louder. try going to a 3 chamber muffler. the 40 series or 2 chamber flowmasters do the same thing as you describe the mac doing. fine for driving around town nasty for a few hour trip. I solved the problem with a new stereo system including 2 12 inch subs. they seem to drone out the drone.
I just installed a mangaflow x pipe with cats on my gt. I had dynomax bullets welded in and dumped. It has more drone than my last setup which was the stock h pipe and 40 series flows. But it sounds awesome, it has a nice rumble at idle and then screams at WOT. At full throttle it has a slight whislte type noise, which people refer to as the raspy sound of an xpipe, it took some getting use to. It kinda sounds like ive got a supercharger under the hood. Either way it turns heads, and it feels like i gained some power down low and up high. I think the x pipe also gives it a sound different than most mustangs. Ive already pissed off some neighbors with the noise, i could imagine how loud an off road would be. But i know some mustang owners who have gotten pulled over and fined for not having cats, so it also depends on where you live. Other than that i was thining about just doing an off road then changing it when smog times comes around. But theres always that chance ill get pulled over by a cop who decides to see if my car has cats. Besides, the off road would probably be way too loud, which isnt always a bad thing. The basic rule is if you use a x pipe, get a straight through muffler like magnapacks or bullets. If you use an h get a chambered muffler. However, i wonder how loud a h pipe would be with bullets, i bet it would sound nice still. With a straight through muffler though, you will either have to get rid of the catback or get a muffler shop to weld up something for you, because your catback is designed for a muffler with a offset inlet and outlet. I might try getting tail pipes back on but for now im happy with the dumps off the bullets. Let me know what you decide on and how it sounds.
Update! Replaced the catco midpipe with a Mac offroad and the drone is signficantly reduced. Before it filled my ears like a fog horn, now its 75% quieter.
i replaced my mac O/R H pipe with a flowtech ( i think ) X pipe and not only did it make my car quieter at idle it reduced the drone from my flowmasters, plus sounded sooooo much better, less old school muscle car sound and more wailing F1 sound
i replaced my mac O/R H pipe with a flowtech ( i think ) X pipe and not only did it make my car quieter at idle it reduced the drone from my flowmasters, plus sounded sooooo much better, less old school muscle car sound and more wailing F1 sound