Exhaust to Meet SCCA Sound Requirements

[JDMac34]

I picked up my new [to me] car a few months ago and have been rocking the previous owner's crazy exhaust setup since then, but I think it's finally time to tame it down a little now that racing season is coming to an end here in NE Ohio. Unfortunately, the previous owner welded the axle-backs to the over-axle pipes, so I can't just swap them out.

Current Setup:
- Kooks long tube headers
- Offroad x-pipe
- OEM resonators
- Roush axle-back

As you can imagine, that setup is pretty loud. I think it sounds amazing when I want it to be, but there is no way that it passes SCCA's sound requirement of 100 dB. I know that most regional events, including all of mine, don't worry about that but I'd like to start attending divisional and maybe even national events. That and I'd like to be able to leave work or go down an onramp without everybody in a 1-mile radius hearing me. I want it to sound good, but I don't want to be "that guy". I really like the idle sound with this setup, and anything up to 3k rpm sounds really good, but it gets loud and raspy as hell as soon as I hit 3k.

For reference, here is a video from my last autocross event. Keep in mind that I'm not running an exhaust mic...

I think that my first step would be to swap the axle-back mufflers for something tamer. I've had my eyes on the Flowmaster FlowFX mufflers (larger square ones, not the round ones shaped like resonators), but open to other suggestions. I haven't found a video of these mufflers on a coyote without cats. I've seen a few videos of 2018+ coyotes without cats and stock mufflers and I'm not a fan - not deep enough.

What does everybody else use that meets sound-level requirements?

 

[JDee]

Stock exhaust with a resonator delete x pipe. Passes sound everywhere. Since it's a stock engine I see no need to do much else. As always, it's about the corners....

 

[DaveW]

As soon as I went to BBK long tubes and catted X pipe on my car, I went from a consistent 93-96db at SCCA events to 105+. I had the fairly small MPRP race mufflers so I switched out to the GT500 OEM mufflers and that got it to 96-100db depending on the conditions. This year, I cut the chrome tips off the mufflers and permanently installed turn downs pointed mostly towards each other that also have Vortex sound cones inside them. This has kept me below 100 and only a few warnings (98 IIRC). The turndowns are there solely to be easily removable to fill the sound cone up with pot scrubbers (tip from Bob Gosda) if I end up going over 100 and have to make an adjustment in between runs.

Honestly, if the long tubes weren't such a biznitch to install, I might have put the stock headers back on just to avoid all the sound issues. I hate messing with that stuff in between runs at National events.

DaveW

 

[JDMac34]

As soon as I went to BBK long tubes and catted X pipe on my car, I went from a consistent 93-96db at SCCA events to 105+. I had the fairly small MPRP race mufflers so I switched out to the GT500 OEM mufflers and that got it to 96-100db depending on the conditions. This year, I cut the chrome tips off the mufflers and permanently installed turn downs pointed mostly towards each other that also have Vortex sound cones inside them. This has kept me below 100 and only a few warnings (98 IIRC). The turndowns are there solely to be easily removable to fill the sound cone up with pot scrubbers (tip from Bob Gosda) if I end up going over 100 and have to make an adjustment in between runs.

Honestly, if the long tubes weren't such a biznitch to install, I might have put the stock headers back on just to avoid all the sound issues. I hate messing with that stuff in between runs at National events.

DaveW

GT500 mufflers were the other ones that I saw recommended a few times. I've seen a couple of cars with turndowns as exhaust tips and wondered what they were for. Can you post a picture of those on your car? Are these what you went with?

 

[DaveW]

I can't find a photo of the back of my car online. I purchased the dynatech turndowns and cones independently, IIRC the outlet on the muffler is 2.5 or 2.75 after you cut the chrome tip off. Also my cone is in the opposite direction as I wanted to be able to fill it up with the pot scrubbers/course steel wool easily. FYI, Bob Gosda, who gave me the idea, runs the scrubbers all the time. I think he said he runs one all the time. He might have louder mufflers than I do, his had a removable chrome tip that he put the cone and stuff inside of instead of the turndowns. Much less ugly than mine. Hopefully he sees this thread.

DaveW

 

[JDMac34]

I purchased a set of Ford Racing mufflers (M-5230 MGTLA). According to the research I did, they are similar to GT500 mufflers but "tuned for the NA 5.0L GT instead of the Supercharged 5.4L from the GT500". The only real difference that I see is that the tips are rolled instead of angle-cut - the sound seems the same based on all the videos that I've seen. I'll try these and hope for the best.

Like I mentioned earlier, the previous owner welded the axle-backs to the over-axle pipes. I took a better look at that last night and noticed an adaptor was welded between the pipes and the mufflers. I'm pretty sure that he used the V6 Roush axle-back kit instead of the GT... Because of that, the majority of the ball flange is still in good shape. I'm thinking about chopping it off just below the weld, cleaning up the mounting surface, and reusing the pipes. Has anybody had luck doing that? I've seen mixed reviews for the ball flange design.

 

[rgosda350]

Here is a picture of my setup, or at least a pic of when I was mocking it up. Just seeing the note Dave mentioned me in November.

The link you had of the turn downs is what I started with. I took the cones out and had them welded inside the removable muffler tips I had. Than as needed to knock sound down the tips can be removed and steel wool, or I used stainless steel pot scrubbers, can be inserted. The cone is really there to hold the pot scrubber in, does very little by itself. I always have one pot scrubber in there to know down the raspiness. Need two sometimes to get to mid 90s db.
Pot scrubber circled in red. I happened to point the cones in towards the muffler. Don't think it really matters.

Bob G.