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Flowmaster Original 40 Series Offset/Offset Oval Muffler; 2.25-Inch (Universal Fitment)

Item 18458
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Market Price $92.15 You Save 12% ($10.60)
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$81.55 (each)

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Ship to: Ashburn - 20149
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      Product Information

      Features, Description, Reviews, Q&A, Specs & Installation


      • Signature Flowmaster Sound
      • Original Two Chamber Technology
      • Offset Inlet and Outlet Design
      • 2.25" Inlet/Outlet Diameter
      • Aluminized Steel Construction
      • Sold Individually
      • Universal Fitment; Modifications Will Be Required


      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 2.25" diameter inlet and outlet in an offset configuration. This is the perfect muffler for the 1979 to 2004 Mustangs. Excludes 1999-2004 SVT Cobra.

      Fitment: 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 Details

      MPN# 42443

      CA Residents: WARNING: Cancer and Reproductive Harm -


      Customer Reviews (19)

      Write a Review

      Ratings Summary

      4.5 out of 5 overall rating from 19 customers

      Installation Time: Afternoon

      Installation Cost: 0-$100

      • July 24, 2019

        5 2003 GT - KingBenji Installation Time: Less than 1 Hour

        Love It

        The item is very Good... OG sound to my 03 Mustang GT I love it and the beautiful color sits just right

        Helpful (0)
      • May 31, 2019

        5 2004 V6 - mykb Installation Time: Afternoon

        Sounds good

        I installed this myself in a few hours. It sounds a lot nicer than the stock muffler.

        Helpful (0)
      • May 08, 2019

        4 2001 GT - buffuhlo Installation Time: Afternoon

        Stock Exhaust and new mufflers

        I wont lie, I was a little disappointed with these. I have an 01 GT with stock exhaust except these. Cold starts and down shift they sound great, lots of pops and crackles. Deep and pretty throaty, Problem is that there isnt enough. The tone drones around 2000 RPM (crusing rpm) and its not as loud as I would like. Accelerating from 1400-1800 rpm and from 2400-3000 they sound great. The drone in between there is a little annoying and you loose sound clarity/definition. It also looses volume the higher you go in the RPM range or if cruising around 2400 rpm. I may be changing these out or looking into a way to increase volume/tone.

        Helpful (1)
      • January 17, 2019

        3 2002 GT - Jfs1291 Installation Time: Afternoon

        Not the sound I expected

        I had something called “speed rex” for mufflers on my car. It was what the previous owner had installed. I wanted these as I have it on my truck and love the throaty sound I get. Unfortunately, the sound I get from these is the same as I had from the old ones. That low tone modern muscle sound. I was hoping it would be more of the old school sound. I am a fan of Flowmaster and their ventury style and I believe in the science. So overall I'm happy they're on.

        Helpful (5)
      • August 28, 2018

        1 2004 GT - WilliamT Installation Time: Shop Install

        Whisper instead of a rumble.

        Very disappointed in loudness. I was expecting them to deliver a rumbling, I got a murmur. I actually cannot tell any difference between after installation and the sound my OEM mufflers put out. Wasted over $400.I would not recommend if you wanted an impressive sound.

        Helpful (6)
      • March 21, 2018

        5 1999 GT - ChrisG Installation Time: Shop Install Installation Cost: 0-$100

        New Edge Must Have!!!!!!!!!!

        I had my Flowmaster 40 series installed over the weekend and I couldn't be happier!!!!!!!! Finally have that deep throaty drone my stock exhaust was missing. Super cheap price and the car sounds amazing now!

        Helpful (6)
      • February 15, 2018

        5 1995 GT - WilliamG Installation Time: Less than 1 Hour

        Sounds Good

        Just starting to restore my Pony. Replaced my 10 year old Flowmasters, that had holes in them that I had welded shut a few years back. My new ones sounds great!

        Helpful (6)
      • October 09, 2017

        5 1994 GT - JohnC


        Makes my car sound like a beast great exhaust I recommend this product

        Helpful (7)
      • September 08, 2017

        5 2002 V6 - JosephS Installation Time: Less than 1 Hour


        I couldn't afford a dual exhaust so I just replace the existing muffler and it sounds good for a single exhaust. I'm very happy with the end results.

        Helpful (12)
      • July 02, 2017

        5 2004 Mach 1 - Bryce Installation Time: Less than 1 Hour

        The perfect muffler!

        They sound absolutely amazing! Paired with pacesetters long tubes and x-pipe on the stock tail pipes, and look perfect. The fit could not be anymore perfect. For being about as loud a flowmaster as you can buy, aside from the outlaw race mufflers, they are definitely not too loud or annoying. The really do sound perfect, and do not drone at cruising speeds. Took 15 to cut stock mufflers out and welded these in place, lined up perfectly.

        Helpful (7)

      Questions & Answers (9 answers)

      5 Top Rated Questions

      how many inches is the chamber?

      Which muffler would be a bit quieter the Flowmaster 40 series or the magnaflow Performance series satin?

      • Sound would be something that is subjective and changes from each person. In our opinion, we feel like the Magnaflow Performance series is quieter.

      Helpful (0)

      Will this be a direct fit to cut out the old muffler and weld in place this one? 03 V6

      • This Muffler was designed to be used on multiple 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.

      Helpful (0)

      Will this be a direct fit on a 03 v6?

      • This Muffler was designed to be used on multiple 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.

      Helpful (0)

      Been 12 years since my last GT, so I recently purchased a 03' GT Convertible. The exhaust is bone stock from front to back. I want to replace the Ford factory mufflers with of course the original 40's. What size do I need for a DIRECT replacement for stock exhaust?? 2.25 inch OR the 2.50 inch?? I've read all the Q A's and I see people using both sizes for direct replacement. Thanks in advance for your help.

      • The stock 2003 GT's exhausts is a 2.25 inch in diameter. I would recommend going with that size.

      Helpful (0)
      Post Your Question
      4 More Questions
      Will these mock up to a 2008 Mustang gt? I'm looking for the original sound I had on my 89,90 and 91 mustangs 1 answer
      Do I get the 2.25 or the 2.50 for a bone stock 2004 mustang gt cause i thought the GT had 2.5? 2 answers
      How much hp does this add and is it more with dual exhaust? I have a 2000 v6 with a dual exhaust and i was wondering how much hp each of these add? and since i have a dual exhaust im going to buy two of them so how much hp would they add with two of them? 1 answer
      I want a flowmaster but I prefer a not too loud somebody can help me , is my first mustang and I don't have experience with the mustang 88 3 answers

      Installation & What's in the Box

      Installation Info

      What's in the Box

      • (1) Muffler

      Tech Specs

      40 Series Delta Flow versus 40 Series Original versus Super Flow 44 Series
      • Minimizes interior resonance
      • Aggressive exterior tone
      • Two Chambered Muffler
      • Made of Aluminized Steel
      • No minimization of interior resonance
      • Aggressive tone inside and out
      • Two Chambered Muffler
      • Made of Aluminized Steel
      • Delta Flow technology minimizes interior resonance
      • Aggressive deep powerful tone
      • Two Chambered Muffler
      • Made of Black Aluminized Steel

      Will It Fit My Mustang

      • Bullitt - 01
      • Cobra - 93, 94, 95, 96, 97, 98
      • Cobra R - 95
      • GT - 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 00, 01, 02, 03, 04
      • LX - 87, 88, 89, 90, 91, 92, 93
      • Mach 1 - 03, 04
      • Other - 79, 80, 81, 82, 83, 84, 85, 86
      • V6 - 94, 95, 96, 97, 98, 99, 00, 01, 02, 03, 04

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