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Discussion Starter · #1 ·
Hi guys,
I will be ordering an axle back exhaust kit at the end of November and just want to get some opinions from you all. I cannot decide between the Pypes Muffler Delete Kit or the Flowmaster 40's kit. I know the Flow's will give me that deep, throaty sound and a little bit more volume (soundwise) while the delete kit is going to be much, much louder. My question is this ... Does either kit give enough of gain at the rear wheels to be a considering factor or no? I am a bit afraid that the police where I live will be all over a muffler delete kit and I have also read a lot of reviews which seem to steer towards hiring an exhaust shop to install the delete kit due to the hangers not lining up right, while the Flow's reviews seem a pretty easy self install. Opinions/experiences greatly appreciated!
 

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The bolt-on FM axle back will provide around 5 - 7 HP (not noticeable while driving), while removing the mufflers entirely will be neutral there. The downside to muffler removal is the loss of low-end torque (very noticeable while driving), and the fact that it's illegal everywhere. Doesn't really matter how loud it is, just removing the mufflers is against the law in every state.

Not only would the car be loud with no mufflers, in my opinion it'll sound terrible, too, with lots of popping. The car will sound like a 50-year-old farm truck. The Flows will be pretty loud, and will have a quality sound.
 

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Discussion Starter · #3 ·
Thank you for the reply and I think you are right. I found some sound clips with both systems compared to stock and like the FMs better. I was not aware of the torque loss so that is a major factor ... Flows it is! Thanks again!amer.gif
 

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Muffler deletes sound awful on these things, I've heard a few in person.
 

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I added FM 40 clones and frankly they are not loud enough. I am adding an X-Pipe to increase the sound. In fact I wish I had installed FM single chamber 10's which I am told are much louder but far more quiet than muffler delete. You can find the clones on EBay for a fraction of the cost of real Flowmasters and they are basically the same product. The only problem with both product is the drone. The only solution is the Ford Muffler which is very expensive. You may have luck on the forum finding a drone free muffler of another brand but you will have it with most if not all except Ford. I cannot tell any HP gain, but love the sound, just want more of it but totally fear a straight pipe. Good luck.
 

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I have the flowmaster outlaws installed and they're awesome. They have a nice deep rumple at idle, and aren't too loud driving (unless you want to hear them, lol). Only took me about an hour to install with a jack and two stands. And this is with stock manifolds and catted H pipe
 

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If you get the deletes and don't like them i have an American Thunder kit I'll trade you :)
 

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I've heard the muffler deletes on these cars and they sounded terrible. I've got Flowmaster 40s on my car now, and I don't really care for them. They're quieter than my Borlas were but louder inside the car with more drone. They have this raspy trumpet when shifting at high rpms, and it isn't the deep tone I'd like. It sounds good, but it's not the best by any means, and I personally wouldn't purchase them. I've also had quality issues with Flowmaster on every set I've ever owned. Two sets on my last truck had the baffles break loose within a year and one on my last car broke loose in 5.

Axle back mufflers will not add power. If anything, a set of chambered mufflers like will lose power compared to stock, but they're still better than open exhaust. Top tier FRPP axle backs may add 1-2 horses at best, so mufflers are not a performance mod, only aesthetic.

I'm currently on my 4th axle back set on my second GT, and I'd have bought the FR500S axle back set from the get go if I could go back. The sound is irreplaceable and there's NO drone. Get Flowmasters or MAC axle backs, and you'll want to drill your ears out on a 4 hour drive because of the drone.
 

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I am sorry to hear that you have experienced issues with Flowmaster products in the past. If anyone on the forum has an issue with one of our products, please message me or give us a call at (707) 544-4761.

In terms of quality, the Flowmaster American Thunder Axle-Back kit for the 2005 to 2010 Ford Mustang GT is made of 409S stainless steel and, like all of Flowmaster's stainless steel mufflers and systems, has a lifetime warranty to the original purchaser that extends for the life of the original vehicle that the product was installed on. Essentially, this means that this kit will be the last exhaust system that you will ever have to buy for your car. Flowmaster's aluminized mufflers and kits carry a 3 year warranty.

Here is a link to the Dyno sheet demonstrating the power gains provided by this Flowmaster Axle-back system. The 40 Series Classic muffler that was used in this kit is not to be confused with the Original 40 Series muffler. The 40 Series Classic muffler is essentially a square-case with Super 44 Series muffler internals that was specially designed for this kit.

Here is a video clip featuring the Flowmaster Axle-Back kit that the OP is considering. Put on some headphones and you will be able to get a pretty good idea of the sound produced by this kit.

 
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