Mufflers for side pipes

[Cobra #3170]

Has anyone on CC tried the new Flowmaster mufflers (12114071) for Cobra side pipes? They are a relatively new product that is made at their R&D facility in Idaho. I am getting so many complaints about the noise level of my car that I am going to have to do something to reduce the sound levels. I cannot even run at most autox venues now because they have dB limits, much less Infineon or Luguna. They told me I would lose some power with these mufflers but that I should be able to pass Infineon sound limits. Are they a double pass design or something else? The drawing shows a 4.5" outer shell diameter with 3.5" inlet and outlet with an OAL of 35" and a muffler length of 30". The dimensions are almost identical to my Stainless specialty mufflers. I really wouldn't mind losing 75 to 100 Hp if I could get this thing to acceptable noise levels for some events.

[Gunner]

I don't think you'd need to lose that much power. Exactly what are you running right now? Are they straight-throughs (cherry bombs)? And what engine and general build?

[Larry Spillman]

You wont lose much power and the added back pressure will allow better tuning of the motor. You may lose about 15hp a dyno pull would tell you where your at do it before mufflers and after.

[Cobra #3170]

Originally Posted by Gunner

I don't think you'd need to lose that much power. Exactly what are you running right now? Are they straight-throughs (cherry bombs)? And what engine and general build?

Current mufflers are Stainless Specialties ,straight through large ID about 2.75 but am not sure.

Engine: Shelby Aluminum Block, 14.7 to 1, raised port Blue thunder heads w/offset TD rockers. 498 CID, roller cam 287/292@.050 .780 lift, 2 1/8 primaries 3 1/2" collector, peak power 7600, peak torque 5500. I think the cam and compression are responsible for a majority of the noise. Flowmaster said I would lose power but could not give me a %. I thought someone might have tried them since they were developed for this market.

[rustyBob]

Have you considered Supertrap mafflers that go on the end of the existing pipes????
you can cut the noise level and not loose a bunch of H.P.

[FUNFER2]

ALL I HAVE TO SAY,.....THAT'S ONE HELL OF A MOTOR !
I wouldn't want to cap that up.

[Gunner]

Originally Posted by Cobra #3170

Current mufflers are Stainless Specialties ,straight through large ID about 2.75 but am not sure.

Straight-throughs are always going to be somewhere between WOW! and TOO DAMN LOUD, I SAID, TOO DAMN LOUD! They'll kill all the really irritating high-frequency noise but not much else.

You need at least some baffling or foldback to hold in the lower-freq engine noise. As noted, a little backpressure is a good thing.

You might be able to have a good muffler shop insert new cores in your existing pipes for a lot less than a full replacement of the muffler sections. A simple glass-packed single fold/baffle will reduce even that monster mill's noise to something well into WOW range.

You will likely need to retune the carb after the change. The backpressure will change airflow a bit.

[Gunner]

Originally Posted by rustyBob

Have you considered Supertrap mafflers that go on the end of the existing pipes????
you can cut the noise level and not loose a bunch of H.P.

Supertrapps typically do what cherry bombs already do - cut the high-end noise that really makes people plug their ears (and cops reach for their citation book), but without dimming the lower-frequency noise. You need some baffling and tuning to bring the engine noise down all across.

'Trapps are useful on many setups because they are slimmer than most glass-packs.

[Wbulk]

What about putting in Dynatech cone inserts. They are stainless and go in the pipe. Summit has them. There is also another brand that I've seen, but can't find it right now.

[cdnus]

3170---You might want to have your existing mufflers checked with a bore scope first.
I had 2.5" S/S mufflers that had a manufacturing defect in them that caused the front baffle to crack. That allowed the packing to be sucked/blown out causing the mufflers to be unbearably loud.
S/S replaced mine N/C with the new design baffle & so far they are good while cruising & quite loud when on the pedal hard, just the way they should be.
If the bore scope has a 90deg. mirror attachment like mine, you will be able to look right into the holes in the baffle for packing. My Snap On scope is long enough to check all the way from the turnout to past the front baffle on my pipes.

Craig

[Cobra #3170]

Originally Posted by cdnus

3170---You might want to have your existing mufflers checked with a bore scope first.
I had 2.5" S/S mufflers that had a manufacturing defect in them that caused the front baffle to crack. That allowed the packing to be sucked/blown out causing the mufflers to be unbearably loud.
S/S replaced mine N/C with the new design baffle & so far they are good while cruising & quite loud when on the pedal hard, just the way they should be.
If the bore scope has a 90deg. mirror attachment like mine, you will be able to look right into the holes in the baffle for packing. My Snap On scope is long enough to check all the way from the turnout to past the front baffle on my pipes.

Craig

Thanks for the suggestions, I don't think it is the packing though because they were loud as hell the day I put them on. I have another set of pipes that have mufflers inside with a cone on the front face, they are fiberglass
and have a 2" ID. These are noticeably quieter than the stainless units
but are still pretty loud. I hadn't thought about removing these old mufflers and installing something else that would baffle the sound but it sounds like a good idea. The units on the car are a completely welded assembly but my old units look like they could be modified with a new insert. The mufflers from Flowmaster are also 1 piece units that I would need to weld a turn out on as well as mounting tab and a retaining tab to hold it to the collector. They sell for about $200 per side not including welding on the extra parts.
I need this thing to be no louder than a modded Z06 or Viper under heavy throttle but I am not sure if that will be possible.

[DanEC]

Originally Posted by Cobra #3170

I think the cam and compression are responsible for a majority of the noise.

You got that exactly right. Trying to quiet down that type of compression and a cam that peaks over 7000 rpm will be tough without strangling the motor to at least some degree.

[Stentor]

You might want to speak with Tom from Tom's Motorsports in Las Vegas regarding some of the pipes that he has fabricated for Cobras that are raced (reduce noise levels without losing too much power).

http://www.tomsmotorsportsinc.com/

[RICK LAKE]

Cobra #3170 You built an animal that will not like being contained. The high compression is a big part of the noise issue. you are about 150-175 pounds higher than motor with 10.0 compression. I only thing that might help is going to a under car exhaust system with 2 sets of mufflers on each side of the car. hemi mufflers where big in the old days, great flow but quiet to drive. I think it will be hard for you to find a side pipe setup to quiet El Monster down. If worst comes to worst, I would be happy to swap you a nice shelby motor for yours, with side pipes for the street. An Oval system will give you a little more ground clearance, just a thought. Rick L. Ps didn't you just take a cannon to a gun fight? That's the rumor, sound more like the truth.

[Ant]

I have seen multiple small diameter perf cores welded into a group fitted to race cars eg. if you have a 3" internal diameter muffler you can fit inside a group of 4 x 1.25" cores which run the length the muffler, a leading motorsport team claims this can reduce noise significantly and possibly up to 60% but I guess that varies and as mentioned in this post high compression is very hard to muffle!

I am going through a similar scenario with my 373 based cup engine and deciding on either 4 or 4.5" diameter outer case, and whether to use 3" or larger 3-1/2" internal perf core, I have the stainless screen material to make my own extra muffling cores. I notice on Vintage Motorsports cobras they use 3" turnouts which I think look better than the 3.5" drainpipes most people use, but I guess if you need a large core you dont need to restrict the end of the pipe.............!

[601HP]

I gotsda know; what are the HP and TQ numbers for that engine? I'd like to hear it bark!

David

[TripWalton]

I have a loose baffle in one of my side pipes. Any suggestions on how to secure it?

[FUNFER2]

Look at mine here.

Side Pipes

[joyridin']

You could try these:

Spiral Turbo Specialties:

Very very little HP loss and they give a deep throaty sound.

[FUNFER2]

Our's do not have tabs to break loose & rattle. Below is a photo of the muffler which has louvers for sound control. (some anyway)

Here's the sound with a FE.
(made it for the buyer of my engine)

YouTube - ‪For buyer of my engine #7‬‏