No exhaust threads any more.

ghunt81

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Let's see I need a couple sheets of drywall...a few 2x4's...a pound of nails, oh and of course, a Borla axle back.

I have noticed more and more of these store websites are like Amazon now...if you can buy it online they list it on their website.
 

eighty6gt

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I've chosen the most difficult/interesting path. Stock Bullitt mufflers. Delete the resonators. Make my merge with 3" inlets and 2-1/2" outlets (headers have 3" collectors,) put a 3" 3 bolt flange on the side of the merge box, put an electric cutout on it, and make a constant cross section outlet that comes out in front of the right rear tire. When the cutout is fully open, the clutch switch for the wotbox will be enabled (relay.)

Quiet for sneaking out of the neighborhood on Sunday mornings, or ridiculous.

Example image chosen because I found it on a site for sale with the notes written on there, hehehehe

A7700127.jpg
 

dotskip

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Borla S Type sound great and are quiet while cruising and off the throttle :)
 

06 T-RED S/C GT

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Except when cruising between 60-70 MPH on the highway in 5th gear at 1800-2000 RPM, the S-Types have a terrible drone with the stock manifolds and stock catted mid-pipe. After nearly 2 years, I finally replaced the Borla S-Types with the Borla ATAK mufflers which made a noticeable improvement.
 

ghunt81

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So I put on my MBRP's with my little bitty resonators. Sounds pretty good, not too bad inside the car, but from the driver's seat it sounds like there is some serious trumpeting at WOT. Funny thing is I punched it on a narrow bridge with jersey barriers on both sides and didn't hear it? So i dunno.
 

eighty6gt

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I'm really enjoying my stock mufflers again LOL.

I think the cutout idea I'm building is going to be pretty ape as well. No resonators, not a god damn thing. Open headers. I'll post a sketch around here when I get the design started.
 

ghunt81

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I thought about reinstalling my stock mufflers to see how they were but don't really feel like wrestling them back on. I took them off 7 years ago and still remember what a bitch it was getting at those hanger bolts on the bottom of the frame.

I also thought about cutouts but a) they're technically illegal here and I'd hate to fail inspection for that, and b) knowing me I would never use them, unless I got electric cutouts but I don't want to pony up for the super expensive ones that won't leak.
 

RED09GT

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Pentalab

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eighty6gt

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The two step will make flames. You can open the cutout any amount you'd like. Get the "exhaust leak on a grain truck" effect all the way to "dodge slant 6 with zoomies in the staging lanes on friday night."
 

808muscle

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Pypes LTs, offroad H pipe, Dymomax midmounted resonators and Borla S Types. Deep and throaty no raspy notes at all. Not N/A either, m90, D rockers cams too.

 

06 T-RED S/C GT

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How bad is the drone with the Borla S Types? I replaced them with the Borla ATAK as I couldn't stand the dreaded drone from the S Types with stock exhaust.
 

808muscle

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How bad is the drone with the Borla S Types? I replaced them with the Borla ATAK as I couldn't stand the dreaded drone from the S Types with stock exhaust.


Longtubes, no cats, cams, its LOUD so you hear it but I wouldnt call it drone with the S types. I tried 5 different setups before the S types....by far the best sounding for what I wanted.
 

06 T-RED S/C GT

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My guess is your Dynomax midmounted resonators are dampening the amount of interior resonance drone produced by the Borla S-Types. Prior to making the switch to the Borla ATAK's, I actually considered looking into splicing in a pair of Vibrant 1792 resonators with the Borla S-Types, but was concerned that adding resonators to the stock cats would not only significantly reduce the overall sound volume, but also just dampen the amount of resonance drone as well. Therefore, I decided in the end to make the switch from the S-Types to Borla ATAK's along with splicing in the Pypes cut n clamp X pipe to the stock catted downpipes which so far have seemed to make a noticeable improvement :shrug:
 

Enfield

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Just got my '07, and it has serious drone problems, first at 12-1500 rpm and again just past 2000. Above 2800 the sound sweetens, but it's garbage down low. JLT3 up front.
Original owner installed BBK LT's - 1 5/8" to 2 1/2", followed by BBK catless x-pipe and Flowmaster Am Thunder - all 2 1/2". Somewhere along the way a PO added M-80's before the axle - no doubt to try to deal with the drone. They didn't work, and with 1" lowering springs they occasionally bottom on hard bumps at higher speeds.
This car is a cruiser, with no plan for track use, so I'm OK with running a lot quieter so long as the tune doesn't get messed up. It appears to be a Bama 93 that came with an old Diablo. Not crazy about the tune, but it gives good economy at cruising speeds. As an old hot rodder buddy put it, a lot of these canned tunes seem to feature hair-trigger throttle response off idle to make you think your car is a fire-breathing dragon.
At some point I'll want to add some grunt to the mid-range, but for now the priority is getting rid of the drone. It seems there are two choices for doing this: replace the Flowmaster AT's with stock-like mufflers, or add a Helmholtz setup. So far, this site's Search function hasn't returned any first-person accounts of a successful Helmholtz installation, but I'm willing to spend a little MIG wire on 2" and 4" pipes to fabricate a system.
The math is pretty simple, so long as you know the offending frequency - which by all accounts is around 80 Hz in the 12-1500 range. If anyone has a more specific number please let me know; I was using a freebie sound spectrum phone app that jumped back and forth between 60 and 120 as I droned along. A Youtube Helmholtz site featured a little chart that suggested a V8's problem frequency is right around 80 at the lower rpm range, so that looks like a good bet to plug into the equation.
The value I'm less sure about is the temperature of the exhaust gases within that 12-1500 range. I have no idea how to measure that within the area of the resonators - short of installing a set of old snowmobile EGT gauges that I used for tuning a road race car. After the 4.6 is warmed up, idling exhaust at the tailpipe is 175 degrees F, but I'm thinking that the critical vibration is coming from up around the M80's. I'm guessing it's 300 degrees F at 1350 rpm there, and have included the recognized speed of sound for 300 in my equation. If I install the EGT's, it will be through holes that can then be enlarged to weld in the J-pipes.
So, with 300 degrees and 80 Hz, the Helmholtz equation indicates that a 10.5" J of 2" pipe into a 4" can that's 8" long will effectively cancel the drone.
All suggestions, comments, criticism and so on are welcomed - including advice on moving this request to a different forum. Sure, you guys have beat the exhaust question to death for years, and every car is a little different with its tune and what-not, but S197forum does not seem to have much practical advice ion Helmholtz that I could find. Plenty of good ideas about exhaust and noise, though.
Enfield - 2007 GT convertible 4.6 5-spd with JLT3, BBK LT and catless X, M80's, and Flowmaster American Thunder axlebacks. Also lowered, and with 3.73's.
 

07gts197

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I’d get rid of those awful flowmasters. Don’t try to reinvent the wheel, it’s much easier to bolt on an axle back.


Sent from my iPhone using Tapatalk
 

eighty6gt

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I never did do the cutout, they are junk.

@Enfield
I may replace my mufflers with MBRP. Straight through design, not very loud. Not sure when as I'm still happy with stockers and just doing without using the 2 step. Look into it! They have two different sets, one aluminized one stainless.
 

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