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Flowmaster 40 Series Offset/Offset Oval Muffler; 2.50-Inch (Universal Fitment)

Item 18433
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Market Price $103.68 You Save 12% ($11.93)
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$91.75 (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
      • 2.5" Inlet/Outlet Diameter
      • 409s Stainless 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 409s stainless 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.

      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# 8042543

      CA Residents: WARNING: Cancer and Reproductive Harm -


      Customer Reviews (20)

      Write a Review

      Ratings Summary

      4.8 out of 5 overall rating from 20 customers

      Installation Time: Weekend

      Installation Cost: $100-$250

      • November 01, 2017

        5 1995 V6 - WayneT Installation Time: Afternoon

        FLOWMASTER 40's (Stainless)

        My last set of 40's, 12 years old still sounded pissah but internals became loose. However they certainly exeded my expectations and money's worth! You will never hear ANYONE say that they aren't a great choice for all Mustang's period.

        Helpful (8)
      • September 20, 2017

        5 1995 GT - WesD

        Perfect vintage sound

        Exactly what every "classic" 5.0 needs...two-chamber Flowmasters!

        Helpful (6)
      • July 31, 2017

        5 2000 V6 - WilliamS Installation Time: Shop Install Installation Cost: 0-$100

        Sounds great

        Replaced my old aftermarket mufflers with 2 of these great sound on my v6 mustang

        Helpful (9)
      • February 16, 2017

        5 2003 GT - JohnnyH Installation Time: Shop Install Installation Cost: 0-$100

        Best sounding Mufflers out there in my opinion

        Sounds great with h pipe nice well-built mufflers have had them on other cars in the past always a good sound

        Helpful (8)
      • October 30, 2016

        5 1994 GT - Rundown Installation Time: Less than 1 Hour


        Tell all mustang drivers to put this on the stang.

        Helpful (7)
      • July 17, 2016

        5 1994 GT - Sn95guy

        Just what i expected

        Combined these with just a off-road h pipe no cat oem headers oem cam. Sounds great. gets complements all the time. Shipped fast easy fit.

        Helpful (9)
      • May 28, 2016

        5 1993 GT - smldbowen Installation Time: Shop Install Installation Cost: $100-$250

        Flowmaster 40's on a 1993 Mustang GT

        Love these mufflers! Great aggressive tone. Installed these with the Flowmaster 2.5" exhaust pipes, Pypes 2.5" flow tubes, and BBK Catted H-Pipe (all purchased here from American Muscle) on our 1993 Mustang GT to replace the aging (and rusted) custom catted H-Pipe, MAC exhaust pipes, and Dynomax mufflers. At idle, these Flowmaster 40 mufflers sound more hollow and a little more aggressive than the Dynomax ones we had on there. Getting up to speed in 2nd and 3rd really makes this car sing now! Cruising in 5th sounds great but no major drone. Would highly recommend these! Not too raspy....perfect for that classic 5.0 Flowmaster sound!

        Helpful (8)
      • December 24, 2015

        4 1993 GT - MustangMain Installation Time: Less than 1 Hour

        Great Sounding Muffler

        If U want that Classic Mustang Sound Original 40 series Flowmasters are they way to go...I had the Super 44 and let me tell u don't waist your time on a Fox Body Original 40 series is the way to go...and they look great under the car!!

        Helpful (10)
      • October 22, 2015

        5 1994 GT - Foxracer5824 Installation Time: Afternoon

        Flowmaster exhaust kit

        Exactly what I wanted! My 1994 gt had a brand new exhaust on it when removed but it was all custom bent and looked TERRIBLE. This kit goes excellent with a bbk x pipe. I would recommend this to anyone and it bolt right in with no fabrication necessary. Looks more than professional when complete and sounds awesome! FANTASTIC PRODUCT! I would definitely buy this again if I bought another car

        Helpful (7)
      • August 27, 2015

        5 1992 GT - 92gt Installation Time: Afternoon

        Hard to beat the sound on a 5.0 !

        Great fit, quick shipping, and a great price for a classic muffler! These sound amazing on the foxbody mustang.

        Helpful (17)

      Questions & Answers (10 answers)

      5 Top Rated Questions

      Will this produce a raspier or a deeper sound on an '04 V6?

      • Flowmaster exhausts will generally provide a deeper exhaust sound.

      Helpful (0)

      Is it street legal I am really trying to avoid getting pulled over by the cops buy still have some great sound

      • The Flowmaster 40 Series Offset Muffler will pass sound code regulations in most areas, however the remainder of your cars modifications, as well as the local regulations will mean that there is no guarantee this will pass local sound code regulations.

      Helpful (0)

      How loud is it I am looking for 95 decibels cause I don't want to get pulled over by the cops I need 2 of this. How many decibels will it be if I buy this

      • Hello! The Flowmaster 40 Series Offset Muffler does not have a decibel rating because the sound level will vary greatly depending on the application.

      Helpful (0)

      How many decibels is it I live in California and the limit here is 95 Decibels so the police won't pull me over

      • Hello! The Flowmaster 40 Series Offset Muffler does not have a dB rating, as it is dependent on the vehicle it is being used with.

      Helpful (0)

      Can this fit on a stock exhaust, can I just take out the muffler and just put the flowmaster one in?

      • Depending on the length of your stock muffler and the location of the inlet and outlet, this could be a direct replacement with the correctly sized clamps. If your stock muffler is shorter than the Flowmaster 40 Series Offset Muffler, additional cutting would be required.

      Helpful (0)
      Post Your Question
      5 More Questions
      Will these fit my stock 02 V6 mustang? 1 answer
      does the muffler have a hanger bracket on the rear of it like the factory muffler does 1 answer
      I currently own a '94 Cobra and would like to utilize the Flowmaster 40 series mufflers. Flowmaster no longer offers this muffler (instead they offer the 44 series muffler) in a full cat back exhaust set up. If I purchase two 40 series mufflers in 2.5in, the 2.5in Stainless Tailpipes (Part #20114), and the the 2.5in Flow Tube kit (Part #20109), will my muffler shop be able to build me a complete catback with these parts? Thank you! 1 answer
      does this product come with the exhuast tips? 1 answer
      Want the stainless steel flowmaster 40's. Are both sides the same? Are the flowmaster 40 mufflers for my 1989 mustang gt the same for both sides or is there a left and right muffler? I need the stainless 2.5". Thanks, Bruce 1 answer

      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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