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Flowmaster Original 40 Series Offset/Offset Oval Muffler - 2.25 in. (Universal Fitment)

Market Price $91.99 You Save 13% ($12.04)
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$79.95 (each)

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  • Item 18458

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    Features & Details

    • 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 -

    What's in the Box
    • (1) Muffler
    Installation Info
    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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    Questions & Answers (7)

    5 Top Rated Questions

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

    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)

    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

    • The Flowmaster Original 40 Series Offset Muffler - 2.25 in. is designed to be a direct fit replacement for 79-04 Mustangs. It will likely require some modification to fit on your 08 GT

    Helpful (0)

    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?

    • I owned a 04 40th GT and had the 2.5 in and out and custom made the h pipe at a local exhaust shop, took out old h pipe, built a 2.5 new with the cross section brought more toward the engine, made it more throatier, then went 2.5 all the way the the rear. If I could submit a pic for I'd show ya, hope this helped

    Helpful (0) Show 1 more answer
    Post Your Question
    2 More Questions
    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

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    Customer Reviews (16) Write a Review

    Overall Rating 4.5

    out of 5 stars

    Installation Time:Afternoon

    Installation Cost:0-$100

    • Loudness / Volume 4.125 4.1
    • Exhaust Note 4.3125 4.3
    • Fit & Finish 4.8125 4.8
    • Bang For Your Buck 4.375 4.4

    • 3/5

      Installation Time: Afternoon

      January 17, 2019

      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.


      Year: 2002 Submodel: GT

      Helpful (2)

    • 1/5

      Installation Time: Shop Install

      August 28, 2018

      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.


      Year: 2004 Submodel: GT

      Helpful (2)

    • 5/5

      Installation Time: Shop Install

      Installation Cost: 0-$100

      March 21, 2018

      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!


      Year: 1999 Submodel: GT

      Helpful (4)

    • 5/5

      Installation Time: Less than 1 Hour

      February 15, 2018

      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!


      Year: 1995 Submodel: GT

      Helpful (4)

    • 5/5

      October 09, 2017


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


      Year: 1994 Submodel: GT

      Helpful (5)

    • 5/5

      Installation Time: Less than 1 Hour

      September 08, 2017


      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.


      Year: 2002 Submodel: V6

      Helpful (6)

    • 5/5

      Installation Time: Less than 1 Hour

      July 02, 2017

      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.


      Year: 2004 Submodel: Mach 1

      Helpful (5)

    • 5/5

      Installation Time: Less than 1 Hour

      March 04, 2017


      Just had dual Flowmaster Original 40 installed on my 03 Mustang GT. Totally satisfied with performance! Amazing sound! Look out Cobras!


      Year: 2003 Submodel: GT

      Helpful (5)

    • 5/5

      Installation Time: Shop Install

      Installation Cost: $100-$250

      February 06, 2017

      2003 mustang v6

      Sounds great for a v6! Almost like a classic v8 sound! A little raspy at higher rpms but I enjoy it! Mufflers seem to be very high quality and would recommend to anyone!


      Year: 2003 Submodel: V6

      Helpful (6)

    • 4/5

      Installation Time: Afternoon

      November 04, 2016

      1995 V6

      This muffler is pretty nice. I have a 95 v6 that I put this on, it gave it a pretty good rumble by just leaving the stock Y pipe setup I just took the old (single) muffler out and replaced it with this one. I took it to a local muffler shop and for about 40-50 bucks and 30 to 45min my car was sounding a bit meaner. I mean it still doesn't purr like a v8 but overall great part, cheap and relatively easy to install.


      Year: 1995 Submodel: V6

      Helpful (7)

    • 5/5

      Installation Time: Less than 1 Hour

      May 30, 2015


      Sounds great. Best purchase yet. Love it highly reccomend this product. Makin heads turn left and right.


      Year: 2000 Submodel: V6 Winslow, ME

      Helpful (7)

    • 5/5

      Installation Time: Less than 1 Hour

      December 18, 2013

      Amazing Rumble 93 Mustang LX 5.0

      The quality of the product far surpasses that of what i expected. theres no doubt i made the right choice when choosing flowmasters.


      Year: 1993 Submodel: Other Los Angeles, CA, USA

      Helpful (8)

    • 5/5

      Installation Time: Less than 1 Hour

      November 11, 2013

      01 gt automatic

      These mufflers sound really good with o/r x and mac longtubes ecpecally goin threw tunnels real deep and throaty


      Year: 2001 Submodel: GT Jasper, AL, USA

      Helpful (5)

    • 5/5

      Installation Time: Shop Install

      Installation Cost: 0-$100

      June 12, 2013

      Definite bang for the buck.

      I can't afford to fully upgrade to a true duel exhaust, so I kept my single exhaust. I bought this muffler and grabbed an exhaust tip that didn't look like the rusty stock tip, had a local guy install it, and for the money this muffler really delivers on a single exhaust V6. It isn't obnoxiously loud, but it's definitely less subtle than the stock muffler, mainly under acceleration of any sort. I paid around $200 total for this upgrade, and it was worth it. I don't think I'm going to be keeping my mustang for much longer, but this is going to make the remaining time with it more enjoyable.


      Year: 2004 Submodel: V6 Warrenton, VA, USA

      Helpful (8)

    • 4/5

      Installation Time: Less than 1 Hour

      April 20, 2013

      Great sound, not too loud!

      I had these mufflers installed to my stock pipes for $80 at a local shop. They have a great sound! Deep, throaty, aggressive, not too loud. Already gotten compliments on the road. These mufflers gave my GT the classic muscle car sound I was looking for. Thanks AM!


      Year: 2000 Submodel: GT Greensboro, NC, USA

      Helpful (5)

    • 5/5

      Installation Time: Afternoon

      February 14, 2013

      Great sound!

      These flowmaster 40's gave me the perfect sound for my mustang. I was dealing with to much drone and these cleared it up nicely.


      Year: 2001 Submodel: V6 King of Prussia, PA, USA

      Helpful (7)

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