M42 Exhaust Help: Magnaflow Cat + Stromung = Drone

[RickInABox]

So I got in on the last Stromung group buy and when I got under the car to install it I remembered that I had the second resonator cut out out due to a leak. (broke and in college at the time)



So to get the Stromung all fitted up correctly since there was no falange anymore and to pass DC emissions (I did pass) I ordered a direct fit catalytic converter from ECS and installed it as well.




While the car was pretty loud before since the stock exhaust was cut and leaking, I wasn't expecting this for all the money I spent. On top of it, going back and forth between my e39 makes it seem unbearable. At highway speeds, 55-70mph and 2.5k-3K rpms, it's hard to have a conversation and by the hour mark it starts to get uncomfortable, I wouldn't be inclined to do a roadtrip in the car. For whatever it's worth, I tried a free decibel reader on my iphone was registering in the 85-95 range.





Does anyone have any experience with this or can anyone suggest an appropriate solution? I bought an additional magnaflow resonator to install in hopes that would quiet it down and help pick up the slack since the magnaflow cat is much less restrictive than the original and there is no post cat resonator like the stock one. I was also looking into a helmholtz resonator added before the cat which might help since it seems to be mostly a higher pitched sound.

[TobyB]

The age- old solution is a resonator midway between the collector and muffler.

Longer and narrower for 4- cyl cars, traditionally.

It's a common problem with aftermarket performance parts-
it's "dyno- tuned" for power, not quiet.

t

[RickInABox]

Well looks like I'm on the right path then since I have that additional resonator now.

Also got the photos working, so for reference I was looking to have the resonator installed after on the piece after the mid flange.

[roguetoaster]

Odd, my Stromung with stock cat section is not obnoxious, and only slightly louder than on OE back section with a small leak or two. That said, I think a 14-16" resonator would be nice, but I am half planning to go turbo, so I'm not worried.

Be sure you have the mid connection sealed, found out mine wasn't sealing well, and had to make a sealing gasket out of some lead sheet. Prior to doing that it was droning on the highway, and I have a 4.45 rear end in my car.

On another note, maybe bring your car to the College Park Friday meet and we can compare exhaust sound.

[RickInABox]

I was guessing that's because the OEM cat is more restrictive / inefficient than the magnaflow one. Yeah Im still hoping one day to get the funds together to do the JakeB kit haha.

Hmmm... I was wondering about that midsection doughnut, the Magnaflow kit didn't come with one like other guys were chatting about. Figured the magnaflow kit didn't need that but it's possible. I did a soapy water test and everything seems to be sealed, but who knows when its under load.

Yeah that'd be great! Is there a FB page or thread on here with the info?

[roguetoaster]

You can check this thread, although we don't post there much: https://www.r3vlimited.com/board/sho...d.php?t=145091 As to FB, no idea.

Officially, an M42 exhaust does not utilize a seal ring, but in my case the alignment between the two parts of the ball/socket seal was off for some reason, so I had to improvise or suffer a perpetual exhaust leak.

Good to know that you're sealed, guess you'll just have to add a resonator.

Also worth mentioning that Stromung uses a resonator on their E36 M42/44 application, but not on E30s, which makes little sense to me.

[robrez]

My M42 Stromung with aftermarket cat and no resonator was too loud too. So I installed a stock cat section and now it’s great.

[RickInABox]

You can check this thread, although we don't post there much: https://www.r3vlimited.com/board/sho...d.php?t=145091 As to FB, no idea.

Well I made it out to the meet, really nice group of people, so I figure I'll be out that way again. Let me know when your going out there so I can compare the exhaust with yours. Although with the nicer weather we've been having, I've had the windows down and it sounds like there is a bit of an exhaust leak, it kinda sounds like a pressure cooker.

I bought some exhaust seal paste so hopefully that will work.

[roguetoaster]

Well I made it out to the meet, really nice group of people, so I figure I'll be out that way again. Let me know when your going out there so I can compare the exhaust with yours. Although with the nicer weather we've been having it sounds like there is a bit of an exhaust leak, it kinda sounds like a pressure cooker.

I bought some exhaust seal paste so hopefully that will work.

Will do.

I also thought of exhaust paste, but decided against it as the set time is too long, and it's an iffy fix at best. Also of note, my lead sheet gasket might have too low of a melting point, so I might have to upgrade to copper.

[RickInABox]

Ah gotcha, do you have link for that?

I was looking at this https://www.summitracing.com/parts/mrg-5960

[roguetoaster]

Ah gotcha, do you have link for that?

I was looking at this https://www.summitracing.com/parts/mrg-5960

No P/N, I'm, just making them out of flat sheets and joining them together in an O shape.

If attempt 2 fails I'll try another option.

[Victell]

Well looks like I'm on the right path then since I have that additional resonator now.

Also got the photos working, so for reference I was looking to have the resonator installed after on the piece after the mid flange.

Did you ever get the resonator installed? How is your drone now?

Im dealing with the same drone. The longer the freeway drive, the more it feels like torture.

[RickInABox]

Alright so a long time coming on this. I did some more diagnosis (shout out to the ChrisFix exhaust leak method) and found that at pretty much every weld from the Magnaflow direct fit kit from ECS was leaking. Made them take that back for store credit.

So at that point I finally started taking it around to shops for them to look at it / offer a quote. Warrenton is a wonderful place of 'Murican muscle, so no one would touch it.

The guys up at Hi-Flow in Manassas were able to help me out and weld in a custom exhaust from the header to the mid-pipe with an additional muffler (looks like a baffle pack muffler). Alright job, but for $550 and cutting off the Strogmund flange and just welding it straight through wasn't exactly professional.

Finally though, the drone is gone and most of the noise is just wind noise now. Sound is still pretty good as far as the exhaust note goes.

TLDR; just skip to getting something custom made.