RobG

In 2019, the stock muffler on my 2005 finally rusted out. I replaced it with an MBRP system from one of the online shops. It was a bit louder, but otherwise it was fine.

In the Spring of 2022, I noticed my EGTs were higher than usual. I did some investigation and concluded the likely culprit was my Cat. A local shop was more than happy to "skin" it for me (get it? yeah, I know, stupid joke).

Ever since then, there has been a ridiculous, mind-numbing drone from 2000-2300 RPM whenever I'm under any load, such as hauling my camper or big enclosed trailer (or both). This happens to fall right in the middle of my powerband where I am when running 62-65 mph. Even up to 72, it's enough to be annoying. At 75 it mostly goes away, but so does any resemblance of MPG.

A few days ago, I had a whole new 5" system put on it (at the same shop that did the "skinning"). The system starts right after the 45-deg bend that sends the pipe aft, so it's not RIGHT at the turbo (or exhaust brake, in my case). The muffler is enormous, but still straight through. The new system is about 75% quieter (out the tailpipe) than before but still has a deep tone to it that sounds great. BUT... the drone was barely affected. It might be 10% quieter, but that's it. I had the system made because I'm getting ready to do Compound Turbos over the winter, which requires a 4" exhaust (and I'll be switching to a 5" inline exhaust brake, but that's another story entirely). I was hoping it'd help with the drone. But it didn't.

I got to thinking. The cat was pretty big. It wasn't very long... 12" maybe? But it was at least 8-10" in diameter if I remember right. Part of me wonders if this thing was acting as something of an "expansion chamber" like on a two-stroke exhaust. Or maybe it was just a good muffler.

Some people tell me the second turbo, with the full 5" pipe, will fix the problem. If I could be sure of it, I'd just deal with it until then. But I'm not convinced.

I see that MagnaFlow has an EPA-compliant 5" cat that is similar in shape to the old cat, but it's $400. And I'm not entirely sure where to have it installed in the system, if I were to get one. I have no problems running a cat as long as it doesn't ruin my EGTs.

So.. what do you guys think?

u2slow

Where does your exhaust end and exit?

On my '93... Once i got mine routed over the axle and aimed gently downward (not side exit), i got rid of all my droning. Also running no muffler.

RobG

Same as always.. out the right rear behind the wheel. I very seriously doubt pointing it downwards is going to fix the drone. The drone started after the removal of the cat.

u2slow

Direction matters. I used to have it straight-piped out the side, and it droned.

So you can either play with the outlet direction, or put more silencing on (cat or better muffler).

westcoaster

Do you have an exhaust tip? An oversized stainless blob that sits on the end of the pipe?

I had drone with my MPRB (With exhaust tip) but went away with a flo-pro exhaust system with no tip.

The difference between the two systems being the exhaust tip and the muffler in that the MPRB had cone shaped punch ins facing the flow of exhaust.
I can't recall if the muffler was tapered to the outlet or not.

The flo-pro was a true 4' muffler from tip to exit with holes drilled in the sides.

I would appreciate other's experiance/observations from aftermarket suppliers.

I see the flo-pro is getting rusty again.