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Flowmaster Original 40 Series Offset/Offset Oval Muffler - 2.5 in. (79-04 All, Excluding 99-04 Cobra)

Market Price $98.99 You Save 13% ($13.13)
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$85.86 (each)

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  • Item 18401
  • MPN# 42543

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Quoted installation from $125

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    Features & Details

    • Signature Flowmaster Sound
    • Original Two Chamber Technology
    • Offset Inlet and Outlet Design
    • 2.5" Inlet/Outlet Diameter
    • Aluminized Steel Construction
    • Sold Individually
    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.

    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

    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

    Customer Photos (7) Submit Your Photo

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    13 Questions / 6 Answers

    Ask a Question

    Which muffler is louder original 40 or super 44s?

    JorgeB

    • 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.

      AMKody

    Helpful (1)

    Will these work on my 98 cobra?

    Trini

    • The Flowmaster Original 40 Series Offset/Offset Oval Muffler will work with a 1998 Cobra.

      AshleyK

    Helpful (0)

    I already have an X pipe on my 03 GT and cold air intake but would this make my car a lot louder or just a little? could you hear me coming down the street with these?

    JordanL

    • The Flowmaster Original 40 Series Offset Muffler will increase the sound of your mustang and give it that classic muscle car sound.

      AM MikeW

    Helpful (0)

    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?

    RandyM

    • 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.

      AMjordan

    Helpful (0)

    Do they still offer a cat back with original 40's?

    BaldTiresMurphy

    • Hey Murphy, The 40 series mufflers are utilized in the Flowmaster American Thunder Catbacks that we carry.

      Cobra_Machine04

    Helpful (0)

    I have a 2002 mustang gt with stock exhaust. Do I need a 2.25 or 2.5 flowmaster muffler. And do they need to be welded or just clamped

    CG

    • The 2.5 inch one is what will line up with your stock exhaust. However, this 40 Series Muffler's outer case measures 4" x 9.75" x 13", so not only will you have to pick the correct diameter but you need to choose something as close to your current size in order for the least amount of modification to make it work.

      JeffAM

    Helpful (0)

    Customer Reviews (41) Write a Review

    Overall Rating 4.8

    out of 5 stars

    Installation Time:Full Day

    Installation Cost:$100-$250

    • Loudness / Volume 3.95 4.0
    • Exhaust Note 4.45 4.5
    • Fit & Finish 4.65 4.7
    • Bang For Your Buck 4.65 4.7



    • 5/5

      Installation Time: Less than 1 Hour

      August 28, 2017

      Awesome

      This muffler made my Mustang sound like it should have from the factory.

      Howard

      Year: 1994 Submodel: Cobra

      Helpful (1)

    • 5/5

      Installation Time: Afternoon

      February 15, 2017

      Flowmasters

      The flowmasters help my SR performance air intake. You can feel the difference in horsepower

      Dexflex

      Year: 2004 Submodel: V6

      Helpful (1)

    • 5/5

      Installation Time: Shop Install

      Installation Cost: $250-$500

      November 24, 2016

      flowmaster the master of exhaust

      Love these flows, they hum, roar, deep and sound sends a message of....DONT MESS WITH ME!

      pumasixtynine

      Year: 1998 Submodel: GT

      Helpful (1)

    • 5/5

      July 25, 2016

      Flowmaster 40

      If you're like me who owns a v6, you are always looking for ways to look and sound like the big boys. Well, these plus Mac long tube headers = OMG. I've never thought that my little 3.8 could sound good. Deep rumble at idle and tons of neck breaking when driving down the road. I would recommend these two products for anyone who has a v6 and want the v8 burbly sound. Hands down the mid I've ever done to my car!

      Stabgfan99

      Year: 1999 Submodel: V6

      Helpful (3)

    • 4/5

      Installation Time: Afternoon

      June 02, 2016

      40 series original

      The 40 series muffler is awesome ! Sounds amazing well worth it ! Really happy. ..

      Grumpy82

      Year: 2004 Submodel: V6

      Helpful (3)

    • 5/5

      Installation Time: Shop Install

      Installation Cost: $100-$250

      December 06, 2015

      meaty sound

      Had this installed at a discount muffler shop. They bent the midpipe and tailpipe, and welded everything together for $150.00. I was in and out in 30-40 minutes. I wasn't about to get on the ground and do it myself, plus I can't weld. Great sound and it arrived in 3 days, so everything worked out great. The price was right and I would definitely use American Muscle again.

      RD

      Year: 1998 Submodel: V6 Cleveland, OH

      Helpful (0)

    • 5/5

      Installation Time: Shop Install

      Installation Cost: $100-$250

      November 05, 2014

      GET THIS MUFFLER

      If you're like me and you're looking for the classic muscle car sound. Well this is the muffler to go with. I spent months looking for the right muffler to go with. I finally pulled the trigger with the Original 40s and couldn't be happier. My 2001 Mustang GT sounds like a true muscle car now. 100% recommend these mufflers over any other style.

      Kane302

      Year: 2001 Submodel: GT

      Helpful (1)

    • 5/5

      Installation Time: Less than 1 Hour

      October 15, 2014

      A modest muffler

      This is a great muffler for anyone who wants a deeper idle rumble and more aggressive exhaust sound when stepping on the gas. At the same time it is a modest amount of noise so if your like me, who lives in the city and neighborhoods. The mufflers will not wake the dead and your not going to get pulled over by a cop for being too loud.

      Revan903PH

      Year: 2003 Submodel: GT Indianapolis, IN, USA

      Helpful (3)

    • 5/5

      Installation Time: Shop Install

      Installation Cost: $100-$250

      September 16, 2014

      Great classic sound, goes well with my O/R X

      My exhaust setup before buying these was O/R X with muffler deletes so I was used to straight up race car exhaust. I had my mechanic throw these on in 2 hours for $200 and I can't stress how amazing they sound with O/R X. Sounds just like my friends '67. Inside the car, very quiet but loud as heck on the outside. Great buy.

      Ryancopester

      Year: 1998 Submodel: GT Bay Area, CA

      Helpful (0)

    • 5/5

      Installation Time: Less than 1 Hour

      January 01, 2014

      Can't beat the classic note of these 40 series mufflers

      I bought these to replace a set of awful sounding mufflers the original owner of my cobra installed. I'm very happy with the classic note of these mufflers. I am very happy to see the quality of flowmaster remains the same it was back in the 90's! I also commend American Muscle for their customer service. There was a small issue over shipping but customer service was quick to communicate and solved the problem fairly and swiftly.

      Jeremy88

      Year: 1997 Submodel: Cobra Florida

      Helpful (5)

    • 5/5

      Installation Time: Shop Install

      Installation Cost: 0-$100

      June 10, 2013

      Flowmaster 40s on divorced dual v6

      Had a full custom exhaust made for my 94 v6 (divorced duals). I started with magnaflows and they were too quiet so i swapped them out for these and they are much better.They have a nice muscle car rumble to them at low rpm and don`t get too raspy at high rpm. Overall a great product I`d recommend these to anyone with a dual setup on a v6 who wants a deep sound.

      Shirk57

      Year: 1994 Submodel: V6 Ohio, USA

      Helpful (1)

    • 5/5

      Installation Time: Shop Install

      Installation Cost: $250-$500

      May 13, 2013

      go all out

      I have 40s on every muscle car I have and to make sure my 02 gt could compare with the sound of the 60's muscle since its legal where im at I completely changed the exhaust removed the cats and did straight pipe back with the 40's and even the tiny v8 in the new edge mustang can keep the sound of a big block

      borocamo

      Year: 2002 Submodel: GT Fruita, CO, USA

      Helpful (2)

    • 4/5

      Installation Time: Shop Install

      Installation Cost: 0-$100

      October 08, 2012

      v6 single exhaust

      It sounds real good in my opinion. I only have CAI and rest is stock. You can hear a difference from 40s and stock muffler. After you break in the 40s then it starts to rumble. Worth the upgrade.

      XSlashDashX

      Year: 2001 Submodel: V6 Texas

      Helpful (1)

    • 3/5

      Installation Time: Less than 1 Hour

      October 04, 2012

      Nice tone

      Sounds good. The inlet and outlet were a little bigger than the measurements on line said they would be, but it wasn't nothing a little extra welding couldn't fix.

      04terminator

      Year: 2001 Submodel: GT Hebron, IN 46341, USA

      Helpful (1)

    • 4/5

      Installation Time: Afternoon

      September 29, 2012

      Good sound

      its a great part if u cant aford the biggest and best package i would recommen it.

      ZachH

      Year: 1995 Submodel: GT New Jersey, USA

      Helpful (1)

    • 5/5

      Installation Time: Afternoon

      July 26, 2012

      Best mufflers you can buy for sound

      I got these installed on my v6 mustang with the "divorced dual" exhaust and compared to what I had before was a Y-pipe with magnaflows, the flowmasters are SO much louder, people don't believe I have a v6... :D

      MiniHorse

      Year: 2001 Submodel: V6 SC

      Helpful (1)

    • 4/5

      Installation Time: Shop Install

      January 27, 2012

      flowmaster 40s

      the 40s sound amazeing i have stock cats with true duel y converter with two and a half inch pipes into 3in stainless tips $60 . its been 6 mounths since the shop instail they still look excellent ive had outher mufflers but nothing has come close to the clasic flow 40s sound and overall performance i have a 2000 3.8 mustang base with a lot of mods so i was looking for a louder meaner non ricer sound with the 40s my 6er sounds mean and ive noticed a mild gain in performace much like adding a cold air intake thanks flowmaster and thanks am

      mustangmax232

      Year: 2000 Submodel: V6 colorado springs co

      Helpful (1)

    • 5/5

      Installation Time: Shop Install

      January 16, 2012

      Sounds awesome!

      Sounds very good. Deep, throaty sound. Went from stock. Would have liked it to be a bit louder, but very happy with it.

      Ken702

      Year: 1994 Submodel: GT Las Vegas, NV

      Helpful (4)

    • 5/5

      Installation Time: Less than 1 Hour

      November 23, 2011

      Classic sound, great build quality

      It's a great product. The sound of a flowmaster is classic. It fit correctly. It was not as loud as I thought it was going to be but, you have to balance volume/exhaust note. This muffler will easily out last my car.

      Brian

      Year: 1997 Submodel: V6 Green Lane, PA

      Helpful (1)

    • 4/5

      Installation Time: Afternoon

      November 02, 2011

      Nice

      Welded these on six months ago and have been pleased ever since. Only problem with install was the factory exhaust tubing is 2.25 inch and the mufflers have 2.5 inch outlets. Just picked up a couple transition tubes from autozone to make it work. Very price effective way to get a very muscular sound out of your car.

      MineralGreyGT

      Year: 2002 Submodel: GT Wilmington, NC

      Helpful (0)

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