Flowmaster Mustang Original 40 Series Offset/Offset Oval Muffler

Flowmaster Original 40 Series Offset/Offset Oval Muffler - 2.5 in. (Universal Fitment)

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50 Reviews 18 Answers

Features & Details

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

Product Resources

Customer Photos (8) Customer Reviews (50) Questions (15) & Answers (18)

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.

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# 42543

CA Residents: WARNING: Cancer and Reproductive Harm - www.P65Warnings.ca.gov

What's in the Box

(1) Muffler

Installation Info

Installation Time: (approx) 2 Hours

Difficulty Level:Light to Moderate mechanical skill required.

Installation Guides:

No guide available for this part yet. Find out how to get up to $200 for writing an install guide.

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

Tech Guides:

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

Questions & Answers (15)

5 Top Rated Questions

Which muffler is louder original 40 or super 44s?

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.

Helpful (1)

I have a 1994 Mustang gt. I want it to sound deeper. What do you recommend? The 40's or the 44's? The X-pipe, or the H-pipe?

The Flowmaster Original 40 Series Offset Muffler - 2.5 in. (79-04 All, Excludes 99-04 Cobra) will give you a throaty exhaust tone whereas the Flowmaster Super Flow 44 Series Offset Muffler - 2.5 in. (79-04 All, Excludes 99-04 Cobra) item #18400 will give you a deeper and throatier sound since it uses Flowmasters Gen II Delta Flow Technology. To answer your second question, an X-Pipe will give you a more raspy sound since the exhaust will flow into the same channel whereas the H-Pipe will give you a more mellow sound.

Helpful (1)

would these sound good on a stock exhaust 1999 mustang v6?

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.

Helpful (0)

Will I have to add any extra pipe when installing these mufflers.Also will it hurt to use clamps is there any mods needed to the engine or not.

As this would be a universal fit there may be some modifications to the pipes needed. There would not be any modifications required to the engine.

Helpful (0)

Will these work on my 98 cobra?

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

Helpful (0)

Not finding an answer? Ask your question! Post Your Question

10 More Questions

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? 1 answer

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

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? 1 answer

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.

Helpful (0)

Do they still offer a cat back with original 40's? 1 answer

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

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 1 answer

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.

Helpful (0)

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? 1 answer

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

Helpful (0)

Will this fit a 98 Cobra SVT? Thanks 1 answer

Hi, This Flowmaster Original 40 Series 2.5 in. Offset Muffler will fit your 98 Cobra.

Helpful (0)

I have a 1997 Mustang Cobra and i noticed these flowmasters come in 2.5 IN and 2.25 IN which ones do i need? 1 answer

Hi, This Flowmaster Original 40 Series Offset Muffler - 2.5 in.is a perfect fit for a 1997 cobra that has a upgraded exhaust system, If your exhaust system is stock the Flowmaster Original 40 Series Offset Muffler - 2.25 in Item #18458 will be a better fit. Here is the link http://www.americanmuscle.com/flowmaster-40series-muffler-225in.html

Helpful (0)

2001 v6 Mustang So if I replaced my Muffler with the Flowmaster 40s, Would my exhaust have a deeper tone? I still have all stock underneath the car. I do have CAI though. Pretty much Stock shorties, stock y pipe and so fourth. Thanks! 2 answers

Yes all flowmaster 40 ' s or other flowmaster all have a deep tone but if you want more volume with the deep tone go with the 10 series
Yes. Changing the mufflers will change the cars exhaust note.

Helpful (0) Show 1 more answer

2? Im new to the whole muffler system my cobra has one and it sounds nice. My fiance has an 04 gt and im going to get her this one but do i need to buy 2? or just 1 all help appreciated 2 answers

You will need two as the car has two mufflers.
buy 2

Helpful (0) Show 1 more answer

install when installing these do the existing short pipe piece on the muffler go over the stock pipes on the car? And can you use exhaust clamps instead of welding as a temp job? 2 answers

yes most auto shops put it over the pipes on the mufflers. and yes but wouldnt leave it that way for long welding would be the best and strongest thing.
I actually welded these on my car 3.5 years ago, and unfortunately do not remember for sure, but I think welding them is the only option.

Helpful (0) Show 1 more answer

Recommended For You

Customer Reviews (50) Write a Review

Overall Rating

4.8

out of 5 stars

Installation Time:Full Day

Installation Cost:$100-$250

Loudness / Volume 4.068965 4.1
Exhaust Note 4.586207 4.6
Fit & Finish 4.758621 4.8
Bang For Your Buck 4.758621 4.8

no one in the world ever gets what they want, and that is beautiful

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5/5

Installation Time: Shop Install

Installation Cost: $100-$250

February 28, 2019

Fox Muffler Swap

I had them professionally installed and welded they look and sound great!!

JeffreyB

Year: 1984 Submodel: Other

Helpful (0) Thanks for your input!
- Loudness (Volume) 5
  5
- Exhaust Note 5
  5
- Fit & Finish 5
  5
- Bang for your Buck 5
  5
5/5

Installation Time: Shop Install

Installation Cost: $100-$250

February 06, 2019

Awesome!

Not quite but not super loud either. Perfect middle ground! Love this and I recommend.

JaredH

Year: 1991 Submodel: LX

Helpful (2) Thanks for your input!
- Loudness (Volume) 5
  5
- Exhaust Note 5
  5
- Fit & Finish 5
  5
- Bang for your Buck 5
  5
1/5
January 30, 2019

did not use

did not use, returned for credit, reordered super 10

SamR

Year: 2004 Submodel: GT

Helpful (3) Thanks for your input!
- Loudness (Volume) 5
  5
- Exhaust Note 5
  5
- Fit & Finish 5
  5
- Bang for your Buck 5
  5
5/5

Installation Time: Afternoon

November 09, 2018

Nice sound

Very nice tone I got with these mufflers my V6 doesn't sound like a rice box anymore and sounds a bit more like a V8 overall very satisfied with this product video on @jairo.mustangv6 Instagram

Sixbangerstang

Year: 2002 Submodel: V6

Helpful (4) Thanks for your input!
- Loudness (Volume) 3
  3
- Exhaust Note 5
  5
- Fit & Finish 5
  5
- Bang for your Buck 5
  5
5/5

Installation Time: Less than 1 Hour

October 15, 2018

Super 44s

I originally used the original 40s and those had finally gone bad (corroded) so I figured I up to the 44s and I 100 love my purchase. Can really hear the cam more at idle and in combination with my BBK shortys and o/r xpipe the sound is just complete to me

DeonK

Year: 1992 Submodel: GT

Helpful (4) Thanks for your input!
- Loudness (Volume) 4
  4
- Exhaust Note 5
  5
- Fit & Finish 5
  5
- Bang for your Buck 5
  5
5/5

Installation Time: Shop Install

Installation Cost: 0-$100

May 19, 2018

Proper Sound

This flowmaster gives your mustang a loud, but not Stupid loud exhaust that in my experience cops don't mind. It's a really nice and deep tone that screams don't mess with me.

Ericd227

Year: 2003 Submodel: GT

Helpful (5) Thanks for your input!
- Loudness (Volume) 4
  4
- Exhaust Note 5
  5
- Fit & Finish 5
  5
- Bang for your Buck 5
  5
5/5

Installation Time: Less than 1 Hour

March 23, 2018

Flowmaster 40 original two chamber mufflers

These mufflers are great give your mustang that original flowmaster sound , you really can't beat the price too

TonyL

Year: 1989 Submodel: GT

Helpful (5) Thanks for your input!
- Loudness (Volume) 4
  4
- Exhaust Note 4
  4
- Fit & Finish 5
  5
- Bang for your Buck 5
  5
5/5
March 04, 2018

Flowmasters

Car had off brand mufflers on it when I bought it went straight to American muscle and ordered flowmasters great product great service

TheresaH

Year: 1989 Submodel: GT

Helpful (4) Thanks for your input!
- Loudness (Volume) 4
  4
- Exhaust Note 5
  5
- Fit & Finish 5
  5
- Bang for your Buck 5
  5
5/5

Installation Time: Shop Install

March 02, 2018

Flowmaster 40 series

Sounds great !!!worth the money !!! Easy to install less than a hour

Peter

Year: 1998 Submodel: Cobra

Helpful (6) Thanks for your input!
- Loudness (Volume) 5
  5
- Exhaust Note 5
  5
- Fit & Finish 5
  5
- Bang for your Buck 5
  5
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 (9) Thanks for your input!
- Loudness (Volume) 5
  5
- Exhaust Note 5
  5
- Fit & Finish 5
  5
- Bang for your Buck 5
  5
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 (8) Thanks for your input!
- Loudness (Volume) 3
  3
- Exhaust Note 4
  4
- Fit & Finish 5
  5
- Bang for your Buck 5
  5
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 (6) Thanks for your input!
- Loudness (Volume) 5
  5
- Exhaust Note 5
  5
- Fit & Finish 5
  5
- Bang for your Buck 5
  5
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 (7) Thanks for your input!
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 (7) Thanks for your input!
- Loudness (Volume) 4
  4
- Exhaust Note 4
  4
- Fit & Finish 4
  4
- Bang for your Buck 4
  4
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 (6) Thanks for your input!
- Loudness (Volume) 4
  4
- Exhaust Note 5
  5
- Fit & Finish 5
  5
- Bang for your Buck 5
  5
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 (9) Thanks for your input!
- Loudness (Volume) 5
  5
- Exhaust Note 5
  5
- Fit & Finish 5
  5
- Bang for your Buck 5
  5
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 (7) Thanks for your input!
- Loudness (Volume) 4
  4
- Exhaust Note 5
  5
- Fit & Finish 3
  3
- Bang for your Buck 5
  5
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 (6) Thanks for your input!
- Loudness (Volume) 4
  4
- Exhaust Note 5
  5
- Fit & Finish 5
  5
- Bang for your Buck 5
  5
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 (9) Thanks for your input!
- Loudness (Volume) 4
  4
- Exhaust Note 5
  5
- Fit & Finish 5
  5
- Bang for your Buck 5
  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 (7) Thanks for your input!
- Loudness (Volume) 4
  4
- Exhaust Note 5
  5
- Fit & Finish 5
  5
- Bang for your Buck 5
  5

Flowmaster Original 40 Series Offset/Offset Oval Muffler - 2.5 in. (Universal Fitment)