Search  for anything...
Flowmaster

Flowmaster 17421 American Thunder Axle-Back Exhaust Kit 2.5 Inch Aluminized Steel 4 Inch Polished 304 Stainless Steel Tips Compatible with 2005-2009 Ford Mustang 4.0L V6 Coupe or Convertible

Based on 69 reviews
Condition: New
Checking for the best price...
$478.95

Buy Now, Pay Later

As low as / mo
  • – Up to 36-month term if approved
  • – No impact on credit to apply
  • – Instant approval decision
  • – Secure and straightforward checkout

Ready to go? Add this product to your cart and select a plan during checkout.

Payment plans are offered through our trusted finance partners Klarna, Affirm, Afterpay, Zip, Apple Pay, and Google Pay. No-credit-needed leasing options through Acima may also be available at checkout.

Learn more about financing & leasing here.

Free shipping on this product

30-day refund/replacement

To qualify for a full refund, items must be returned in their original, unused condition. If an item is returned in a used, damaged, or materially different state, you may be granted a partial refund.

To initiate a return, please visit our Returns Center.

View our full returns policy here.

Availability: Only 10 left in stock, order soon!
Fulfilled by Holley Performance Product
Arrives Wednesday, Nov 18
Order within 12 hours and 19 minutes

Available payment plans shown during checkout

Protect Your Purchase

Easy claims online, fast replacements, no fees

Checking for protection plans...

Recently Viewed

At a glance

Condition
New
Weight
19.6 lb
Color
Black
Material
Plastic
Vehicle Service Type
Car
Automotive Fit Type
Vehicle Specific Fit
In the box
Flowmaster 17421 Axle-back System - Single Rear Exit - American Thunder - Moderate Sound

Features 8

  • Includes Hangers and Hardware for an Easy Installation
  • Mandrel bent 16-gauge Aluminized Steel Tubing
  • Moderately Aggressive Exterior Exhaust Tone
  • Dyno Tuned for Maximum Performance

Specs 20

Color Black
Brand Flowmaster
Material Plastic
Vehicle Service Type Car
Automotive Fit Type Vehicle Specific Fit
Brand Name Flowmaster
Manufacturer Part Number 17421
Number of Items 1

Frequently asked questions

If you place your order now, the estimated arrival date for this product is: Wednesday, Nov 18

Yes, absolutely! You may return this product for a full refund within 30 days of receiving it.

To initiate a return, please visit our Returns Center.

View our full returns policy here.

  • Klarna Financing
  • Affirm Pay in 4
  • Affirm Financing
  • Afterpay Financing
  • Zip Pay in 4
  • Financing through Apple Pay
  • Financing through Google Pay
Leasing options through Acima may also be available during checkout.

Learn more about financing & leasing here.

Similar Products

Top Amazon Reviews

Absolutely A+. Breathed new life into my ride
Style: Base Product
Installation wasn't hard at all, getting the old muffler out was harder. Here's a quick guide, since I couldn't find any good videos on removing the factory. There are two hangers that support the factory muffler, as well as some sort of rubber band on the back. The hangers came out pretty easily (13mm bolts, ratchet worked with most of them but I needed a wrench for one just due to the position). The rubber band hanger thing wouldn't detach and wasn't really important anyway, so I just cut it off. Getting the muffler off of the car's exhaust pipe was the hardest part. There's a little nub that fits into a cut in the factory (and flowmaster) muffler. Douse the entire connection with as much WD-40 as you can find, then twist that sucker back and forth while pulling it forward and down. If all else fails, whack the connection with a hammer a couple times to loosen up the joint. Whack the ring on the connection a few times too, but mine was welded onto the factory muffler. Once the old rusty factory one is off, grab your shiny new Flowmaster, put the included clamp ring around the not-shiny end, and shove that thing over the factory pipe. Remember that nub- you'll have to fit the little cutout around it. Once it's all the way on, move the ring to right around the nub (Mine is maybe 5mm before the cutout for it) and tighten it down pretty much all the way. That's solid steel, so it'll hold up the muffler well enough so you dont have to hold up 15 pounds of steel while trying to bolt stuff on. Then slide the two muffler hangers around the pegs on the top (and just ignore the peg at the back, that's where the rubber thing would connect but it really doesnt matter) and start bolting it up. Make sure you've got the tip in the right spot before securing it down. Once everything is in place, get all that stuff nice and tight, start up your stang, and enjoy that beautiful sound. It'll smell like burning plastic for the next little while since there's some junk inside of it that might melt, no biggie. Review-wise, I absolutely love this muffler. Sounds amazing, but not loud. I honestly think it sounds better than a stock GT. It's not annoyingly loud, and at moderate radio volume I can't notice the exhaust at all, but when I hit the gas it sounds AWESOME. This is also the cheapest I can find it anywhere ($270 on AM and other sites, I got it for $220 on Amazon) so just buy this. The Pypes just makes a lawnmower sound, this is absolutely worth the extra money! ... show more
Reviewed in the United States on August 15, 2018 by Grant Fowler
nice but....
Style: Base Product
sounds great...install was super easy....waaaaay overpriced for what it is
Reviewed in the United States on May 21, 2025 by Kirt J.
Easy Install, Great Sound, Definite Performance Improvement
Style: Base Product
I bought this axel back system because I was never happy with the sound from my V6. I had previously tried a GT Take Off Muffler (an exhaust removed from a new GT) and while it sounded a little better than stock it was simply not good enough. I just fitted this Flowmaster in under 45 minutes and went for a 10 minute test drive. Yes it is that easy to install this on a 2007. The sound is great, much deeper than before, louder but not too obnoxious. No drone on the highway but a great sound everywhere else. I would highly recommend this exhaust. No it wont sound like a V8 but it certainly sounds more muscular as it should, and there is a definite performance improvement. Overall I am very happy with this purchase. I had considered going to true dual exhausts but in the end the cost just for an improved sound, didnt make sense. One last thing to mention, the exhaust has been on the car for a week and it sounds better than when it was first installed and there is a definite performance improvement. Flowmaster claim 10 HP and I can certainly believe that. ... show more
Reviewed in the United States on November 17, 2010 by David Moore
Rattle Rattle Rattle!! Terrible and NOT the quality I expected from Flowmaster!
Style: Base Product
Finally got this installed (on my sons 1st car) and there is a terrible rattle from INSIDE the muffler! We couldn't figure out what the sound was and started tapping around and it sounds like there are loose pieces of metal (like small balls) inside the muffler! We even ordered a 2nd one and OFF THE CAR, before even installing it, shake it and it rattles too, with small pieces rolling around inside! Flowmaster, if you read this, you should know that you are quickly loosing two young men (and their dad), and I'm sure EVERY friend they will ever talk too!! After recommending this to my son, and investing time and money... I am pissed that the experience. Opening the 2nd box, it was FUNNY and ironic to see a quality inspection sticker... which means either an 'inspector' should be fired, or 'quality inspection' is total BS!!! I almost went with the Pypes Performance Exhaust, but THIS was on prime... WHAT A MISTAKE to trust the Flowmaster brand!!! NEVER AGAIN! ... show more
Reviewed in the United States on August 20, 2020 by Christopher
Great upgrade for a V6
Style: Base Product
I have had this installed in my 2006 V6 mustang for a few years now and have been happy with it. The installation was pretty easy (took me less than an hour). I had no experience working on cars either, so you don't need to be an expert. The sound is definitely better than stock and well worth the money in my opinion. It does 'pop' a bit when cold, but this seems to disappear after the car has been running for a few minutes. ... show more
Reviewed in the United States on November 5, 2010 by Wormer
Bad design over priced
Style: Base Product
Review Image by rooster
Review Image by rooster
Came dented as in pic's, the hangers are to short banged against the frame, the pipe that came out was up against the plastic bumper melted the top and blistered the paint. no adjustment. Had to take it to a muffler shop to have longer hangers and add a piece of pipe to make it fit correct, Has a loud drone at lower speeds, you would think that flowmaster would build it right for as much as they charge. ... show more
Reviewed in the United States on January 16, 2020 by rooster
Here comes the Thunder
Style: Base Product
I installed this on my 05 convertible and what a difference over the stock muffler. The sound is very impressive on acceleration and has a nice deep growl to it when idling. The install took about 2 hours only because the previous owner had the bolt connecting the stock muffler to the pipe welded on. A sawzall took care of that pretty quickly. After that it was just a matter of removing a few hangers and getting the old muffler off. I had considered converting the system to a dual exhaust but this worked out just fine with much less hassle. Very good value for the money. ... show more
Reviewed in the United States on June 28, 2017 by Chuck B.
EEHHH!
Style: Base Product
Sounded pretty darn good for the first couple months......Now it sounds like a FART BOX!!!
Reviewed in the United States on January 12, 2016 by Hunter
How it works
Checking for best price...