How to quiet the COBB CBE exhaust boom... help

I've looked around here AND other sites regarding sound deadening, and I'm still not 100% clear on what exactly is bunk, and what's a viable option for reducing the boomy exhaust I'm getting from my COBB CBE.

 

I've looked at plenty of sites with pricing, claims and some of the sticky threads or links here that are years old now.

 

If I have more than 2 people in the car, and doing highway speed, the drone of the exhaust is pretty loud in the cabin. Hit an incline or hill, and forget it, you can't talk because of the boom.

 

I need to know what product to use, and WHERE to put it in the vehicle to stop this. Does it have to go under the entire floor? Is it just a trunk bottom liner? How thick?

 

Most of the threads I found here are from 2-5 years old, and I wonder if there are new techniques or products out.

 

Thanks

just add a resonator. or under the carpet will do with some sound mat.

just add a resonator. or under the carpet will do with some sound mat.

Or maybe a small high flow muffler at the end of the mid-pipe.

Like the others said, adding a large resonator or a secondary muffler is the way to go.

 

The latter will give you more volume control, particularly if you're a wagon, but I'm honestly not sure about how that may or may not affect flow, if you're "Stage II" or above.

 

A resonator typically takes the harshness - and some resonance - out of the exhaust note, but the ability of it to control volume will pale in comparison to that of having another muffler in the system.

 

Other than that, like quick4dr said, it'll be about sound-control matting in the cabin areas, as well as, obviously (and the very first thing that you should do), checking your exhaust-tract to be sure that there isn't any leaks caused by broken piping or blown gaskets.

I am fighting this same battle( autospeed cbe).

 

I ordered one big roll of b-quiet ultimate and two rolls of v-comp. Installed it all in the trunk and under the back seat. Cost: approx $280 plus five hours install.

 

FWIW I am having a Borla xr-1 sportsman series welded in place of the resonator tomorrow morning. I'll try and get some clips. The deadening just didn't do enough.Cost $110 plus install. I'm actually going to try and get the shop to fab a new mid pipe with the xr--1 so I can keep the autospeed intact.

Where exactly is the "boom" coming from? Does it come from the trunk area, or the midpipe, or even the downpipe?

 

From the passenger perspectives, it's noisy but quiet up front. From the back seat they say it sounds like you're at a racetrack the entire time. I had someone else drive my car while I sat in each seat of the car and confirmed this.

 

I would assume that this noise is coming from the Y pipe to axle back part (the actual cans)... which would tell me to put lining on the trunk bottom, back and possibly the back of the seats and under the back seat, and the console around the e-brake.

 

If what Code wrote, lining does minimal reduction, that the exhaust volume is more in the (lack of) a resonator.

 

I personally love my Cobb exhaust note. It's a biting 2-toned sound of awesome when you get on the gas. What I don't like is my entire house rattling while the car warms up, and that the "Drone" note is exactly where the accelerator is for cruising.

 

My exhaust has 4 parts. The Mid Pipe, the Y Pipe, 2 Mufflers. Without getting into it, I assume that the resonator takes the place of the midpipe? My exhaust is also 3" wide, does that effect it?

 

Part 2: OF all the brands out there, I keep seeing people using b-quiet. Is this a very good product?

Yes, the resonator goes into the mid-pipe portion. If you're the one who removed your factory system, you'll remember how gigantic that resonator was.

 

You should be able to get a resonator that accommodates 3" piping. My previous mid-pipe was a custom-made piece by Lachute, using a rather gigantic Magnaflow resonator in the mid, so I don't know what part number was used (I'd bought it new, as-is, from PLTek), but that does demonstrate that the part's available.

 

If the Cobb is non-resonated (and IIRC, it is not resonated), adding a resonator will help - but my view of things has always been "resonator = tone," and "canisters = actual noise control."

I have a Cobb turbo back and suffered the drone too.

 

For $80 installed, I got a 3" ID SS resonator in the mid. Same tone, about 50% quieter. It's still loud enough to turn heads in a parking lot. And sounds great in the cabin. If you go this route, spend a little extra dough to have a new mid fabbed with the rez. That way, you'll have the original mid-pipe to re-install if you want. I regret not doing that.

Where's the best place to buy the soundproofing materials?

 

Oh and a link to a quality stainless resonator for the OP: http://vibrantperformance.com/catalog/product_info.php?cPath=1021_1033_1054&products_id=293

ok so that resonator is 18" long... I imagine I would have to have a custom fab exhaust midpipe made with it? or hacksaw out 18" of my midpipe and weld it in myself, correct?

ok so that resonator is 18" long... I imagine I would have to have a custom fab exhaust midpipe made with it? or hacksaw out 18" of my midpipe and weld it in myself, correct?

Yes, i would just get the shop to cut a section out of your mid pipe and weld in the resonator and voila, instant noise reduction, I believe they sell a 12" long resonator as well.

^ That's certainly the fastest way to do it.

 

But I'm in agreement with Wang Lung from above - that if I had the extra cash and/or time, to get a custom mid-section fabricated to incorporate the aftermarket resonator.

 

That way, it'll keep the Cobb mid intact, for potential resale and/or when and if the fab'ed resonated mid fails.

 

There's really not much trick to the mid, in terms of pipe bends/runs. It shouldn't cost too much to get it done.

I was surprised at how quiet my exhaust was after the modifications. I have removed the CB resonator and both muffers have been replaced with pipe. I'm using the stock DP and Stock tips welded on the end of 2 small resonators where the muffers used to be.

The xr-1 is installed and is SWEET. Still very deep and rumbly but no more drone. Sounds mean at WOT. I tried to get some clips but my craptastic point'n'shoot doesn't do any justice.

^ Cool!

 

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T-56, that's most interesting!

The xr-1 is installed and is SWEET. Still very deep and rumbly but no more drone. Sounds mean at WOT. I tried to get some clips but my craptastic point'n'shoot doesn't do any justice.

 

What was the total cost for this fix?

The muffler was $115 from Summit and install was $50

The muffler was $115 from Summit and install was $50

 

Was there any midpipe fabrication or did you hacksaw the existing pipe?

Unfortunately the shop didn't have flanges that would mate to the autospeed y. They cut the resonator out and welded the new piece in. Wouldve been nice to have a new one fabbed but I didn't want to wait for them to order the stuff tuen make the hour drive back. Overall I am extremely happy. I no longer feel like some ricer when I pick up a date! :-)

So the drone in the cabin goes way down? That's cool. But you're saying WOT sounds good, does the exhaust outside still have that gritty 2-tone? I love my COBB exhaust, especially when I get on it. Does the boom come back in the cabin when you go WOT?

The (lack of a) resonator is usually the key factor in drone/boominess in the cabin... even moreso in a wagon.

 

I had removed the factory resonator at one point and ran with just a custom axleback Magnaflow muffler setup. It droned. I replaced the resonator and was happy to have it civilized again.

 

I've now installed a cxlighting resonated CBE (on my 2.5i) and it's quite a bit louder. No real drone however but it is louder than what I had. I'm putting down mass loaded vinyl (the active ingredient in the aforementioned VComp from B-Quiet) on as much of the floorpan as I can but particularly good coverage in the rear hatch area. I expect it should make quite a difference.

 

I still want the loud exhaust, but also want to be able to have it nice and quiet inside the car when I want too. I can always open my windows to hear the exhaust if I choose to

I've got a similar issue with my Perrin. I love the sound but it is loud in the cabin. I'm going to try some dynamat in the trunk first. If that doesn't work then xr-1 sounds like a great solution. I would definitely look to fab out a new mid pipe so that I could keep the perrin intact.

From the outside the exhaust is still deep and mean . You can definitely tell that it's not stock at any rpm above idle. I have no drone anymore. For comparison sake, at stock my radio lived at volume 6-8. Autospeed cbe in original form(w/ 4" dia resonator) volume was 11+,yes it was bad. Now w/ borla my radio Volume is 7-9.

 

The borla didn't change the tone at all, just cut volume. It's still deep and rumbly, jst not obnoxiously loud

Have you silenced the boom?

Pros and cons here. I went with the 18" straight-through design resinator in the mid-pipe of my Cobb. They took out the mid pipe, mounted it in a bracket, sawed out the section and welded in the resonator.

 

It went from sounding like a racecar (on the inside) to more of a muscle car. You can still hear the exhaust, especially WOT, but it's cut down probably to 40% of what it was. If I wanted to go further inside, I would probably go for liner, but it's not worth the cost at this point.

 

The "bite" of the exhaust isn't so sharp anymore from the "neighbors point of view". He's a young kid and he loved the way my exhaust sounded before, but now he says it's muffled a bit, almost like talking with your hand about 1" infront of your face.

 

Problem solved? Yes. Suggestions? I'd go for the shorter resonator if I had to do it again... there was a 12" one as well. Would have meant less cabin quiet, but a grittier tone.

 

Cost was about $200 for parts + labor at excelerate in Branford, CT. Resonator was the one depicted on page 1.