2024-2025
2015-2023
2010-2014
2005-2009
1999-2004
1994-1998
1979-1993
Installation Time
(approx) 2 Hours
Difficulty Level:
Light to Moderate mechanical skill required.
Installation Guides
No guide available for this part yet.
FREE 1 to 3-Day Delivery on Orders $119+ Details
Talk to a Mustang Sales Tech
1-877-887-1105
M-F 8:30A-11P, Sat-Sun 8:30A-9P
-
Add Details
- Change Vehicle
- Mustang Builds Gallery
Find Exhaust Accessories for your Mustang
Flowmaster Original 40 Series Offset/Offset Oval Muffler; 2.50-Inch Inlet/2.50-Inch Outlet (Universal; Some Adaptation May Be Required)Find parts that fit my vehicle
Item 18401
Mustang Sales Tech
Verify parts fit & get product recommendations
M-F 8:30A-11P, Sat-Sun 8:30A-9P
$0.00
65 Reviews
15 Answers
Our Price
$99.95 each
Ship to: Enter Zip
Please enter a valid US or CA postal code
We're sorry, zip can't be updated at this time.
Choose options to add to cart.
Saved - View your saved items
We're sorry. We couldn't save this product at this time.
or use
Frequently Bought Together
Product Information
Features, Description, Reviews, Q&A, Specs & Installation
Description
That Flowmaster Sound. Improve your Mustangs exhaust flow for an increase in horsepower and a deeper throatier exhaust note with a set of Flowmaster 40 Series Mufflers for a truly classic muscle car sound.
Superior Design. The Flowmaster 40 Series Mufflers are MIG welded from durable 16 gauge aluminized steel for durability and value. The 40 series mufflers use Flowmasters original two chamber design to increase power and sound. And each muffler is embossed with the "Flowmaster" name so you know it is the real article.
Modifications Required. This Muffler was designed to be used on mutliple applications, as it is not a direct fit replacement part. In order to install this Muffler properly on your vehicle, some modifications to the exhaust system will be required.
Application. The 40 Series Muffler's outer case measures 4" x 9.75" x 13", and features a 2.5" diameter inlet and outlet in an offset configuration. This is the perfect muffler for the 1979 to 2004 Mustangs. Excludes 1999-2004 SVT Cobra.
Superior Design. The Flowmaster 40 Series Mufflers are MIG welded from durable 16 gauge aluminized steel for durability and value. The 40 series mufflers use Flowmasters original two chamber design to increase power and sound. And each muffler is embossed with the "Flowmaster" name so you know it is the real article.
Modifications Required. This Muffler was designed to be used on mutliple applications, as it is not a direct fit replacement part. In order to install this Muffler properly on your vehicle, some modifications to the exhaust system will be required.
Application. The 40 Series Muffler's outer case measures 4" x 9.75" x 13", and features a 2.5" diameter inlet and outlet in an offset configuration. This is the perfect muffler for the 1979 to 2004 Mustangs. Excludes 1999-2004 SVT Cobra.
Flowmaster 42543
CA Residents: 
WARNING: Cancer and Reproductive Harm - www.P65Warnings.ca.gov
Installation & What's in the Box
Installation Info
What's in the Box
- (1) Muffler
4.8
Customer Reviews (65)
Review Summary
Installation Time: Afternoon
Installation Cost: $2.00
Mar 14, 2024
2007 GT - DBentley
Installation Time: Afternoon
Good sound
Sounds way more throaty and aggressive then the stock mufflers. Not to loud
Fit & Finish 5/5
Loudness (Volume) 4/5
Exhaust Note 5/5
Bang For Your Buck 5/5
Mar 14, 2024
1986 Other - Zo8
Installation Time: Afternoon
Sound clean on my 86 5.0
Sounds great, not too loud at idle. Running original cats and bbk headers.
Fit & Finish 5/5
Loudness (Volume) 3/5
Exhaust Note 4/5
Bang For Your Buck 5/5
Mar 27, 2023
1996 GT - BryonLough
Installation Time: Afternoon
Exhaust
Flowmaster mufflers have always been a good product well-built and sound great.
Fit & Finish 5/5
Loudness (Volume) 3/5
Exhaust Note 4/5
Bang For Your Buck 4/5
Aug 10, 2022
2002 GT - BenjaminA
Installation Cost: 120
Installation Time: Shop Install
Classic Muscle Roar
I love the sound of this muffler. It’s loud but not too loud where you wake up the whole neighborhood. I highly recommend this muffler for a V8 mustang!!
Fit & Finish 5/5
Loudness (Volume) 4/5
Exhaust Note 4/5
Bang For Your Buck 5/5
Oct 22, 2021
2000 V6 - StangLifeTN
Installation Time: Less than 1 Hour
Best sound I've heard with single exhaust
Did a cat delete Installed 40 series muffler Stayed with single exhaust Had a lot of compliments on the sound
Fit & Finish 4/5
Loudness (Volume) 3/5
Exhaust Note 4/5
Bang For Your Buck 4/5
Aug 12, 2021
1999 V6 - JaimeT
Installation Cost: 0-$100
Installation Time: Shop Install
40 original flow master
It’s good sound better that others I love it sounds like a v8
Fit & Finish 5/5
Loudness (Volume) 4/5
Exhaust Note 5/5
Bang For Your Buck 5/5
Jan 16, 2021
2001 GT - CAR3Y4
Installation Time: Afternoon
Flowmaster 40 series
Sounds amazing. I'd give it 6 stars if I could. I paired it with my BBK Off-road X Pipe and I got it installed at my local muffler shop.
Fit & Finish 5/5
Loudness (Volume) 4/5
Exhaust Note 5/5
Bang For Your Buck 4/5
Jun 23, 2020
2007 V6 - DBalf03
Installation Cost: $100-$250
Installation Time: Shop Install
Flowmaster original 40
Great rumble, smooth sound for a v6. Recommend to any 05-09 mustang
Fit & Finish 5/5
Loudness (Volume) 5/5
Exhaust Note 4/5
Bang For Your Buck 5/5
Apr 15, 2020
2002 GT - MustangKeys88
Good Classic Mustang Sound
What can I say, it's the perfect combo with a 4.6 2v. No droning at highway speeds either, not too loud, but loud enough
Fit & Finish 5/5
Loudness (Volume) 4/5
Exhaust Note 4/5
Bang For Your Buck 5/5
Apr 11, 2020
2000 V6 - T
Installation Time: Afternoon
Great. Sound
Flowmasters 40s look well made and heavy materials in this product.the sound is amazing with flowmasters hi flow cats offroad h pipe these 40s and 2.5 tailpipes .Thanks American Muscle.
Fit & Finish 5/5
Loudness (Volume) 4/5
Exhaust Note 4/5
Bang For Your Buck 5/5
Questions & Answers (15)
5 Top Rated Questions
Q: Which muffler is louder original 40 or super 44s?
A: Honestly, they are very very close in overall sound, but the super 44's are slightly louder, the original 40's are a little deeper.
Q: could i take off my stock muffler on my 04 mustang 3.9L v6. and put this on without any problems and would it sound better?
A: Yes, you would be able to install this on a 2004 3.9l V6 mustang. The sound being better would be personal preference, it would increase the sound of the car with this muffler.
Q: I have a 2012 Mustang GT. I took off the stock mufflers and ran straight pipe, axle back. I hate it, its WAY too loud. I want to put FLowmaster40s on, does anyone know how these sound on the 2012?
A: This Flowmaster Original 40 Series Offset Muffler - 2.5 in. is for a 1979-2004 Mustang GT and will not work on a 2012. I would recommend checking out our axle-back exhausts for your 2012 Mustang GT. I will put the link to our selection below. http://www.americanmuscle.com/2010-mustang-axleback-exhaust.html#shop-by3
Q: would these sound good on a stock exhaust 1999 mustang v6?
A: These will offer a more aggressive exhaust tone when compared to the factory. If that is what you're looking for, I would definitely recommend.
Q: Will these work on my 98 cobra?
A: The Flowmaster Original 40 Series Offset/Offset Oval Muffler will work with a 1998 Cobra.
10 More Questions
