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Flowmaster 40 Series Delta Flow Aluminum Performance Muffler 9425422

Product Information
Our Price: $97.26
Part #:9425422
Body Style:Aluminized Steel 13" Muffler | Center Inlet & Dual Outlet
Size:2.5" Inlet & 2.25" Outlet | 4" x 9.75" Body
Application: 2.5" Inlet / 2.25" Outlet (Center In - Dual Out)
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Ships Oct 25th - 26th


  • The "Original" Flowmaster: The 40 Series Delta Flow muffler is Flowmaster's original design. For over 25 years enthusiasts have relied on the 40 for cutting edge performance.
  • Deep, Powerful Tone: If you want to hear your car or truck's throaty sound, the 40 Series muffler is for you. It offers a very aggressive tone that sounds great on vintage and late model vehicles.
  • Increased Horsepower: The Original 40 muffler features a baffled internal chamber that increases horsepower and torque with unrestricted exhaust flow.
  • Reduced Interior Resonance: Flowmaster relies on a chambered internal design to tune your exhaust note and reduce interior drone and resonance.
  • Aluminized or Stainless Steel: Flowmaster offers the Original 40 series muffler in an aluminized steel finish or 409 stainless steel for enhanced corrosion resistance.
  • Made in the USA - Santa Rosa, CA


The 40 Series Delta Flow muffler utilizes Flowmaster's original design, developed over 25 years ago. It's chambered internal design offers a deep, powerful tone that screams performance for your car or sport truck. The 40 Series muffler's internal design tunes your vehicles exhaust tone for that unmistakable "Flowmaster" sound. It also allows for unrestricted exhaust flow increasing torque and horsepower numbers. The 40 Series Delta Flow muffler has a case dimension of 13"L x 9.75"W x 4"H, and and overall tip to tip length of 19". They are available for 2"-3" exhaust systems. Flowmaster offers the 40 Series mufflers in aluminized steel as well as 409 Stainless Steel for unmatched corrosion resistance.

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Frequently Asked Questions

What is Flowmaster's warranty?
All Flowmaster products built of aluminized steel have a 10 year limited warranty against defective materials and workmanship. All stainless steel mufflers have a 10 year limited warranty against defective materials and workmanship.

What is "Delta Flow" technology?
Flowmaster's "Delta Flow" technology has evolved from extensive Research & Development at race-tracks around the country. This new technology provides superior scavenging while reducing resonance inside the vehicle. What you can expect is improved performance while maintaining a pleasant tone, both inside and outside the vehicle.

What materials are used to build Flowmaster mufflers?
All Flowmaster products are fully mig welded and built from 16 gauge aluminized steel for durability and value. Specific part numbers of the 40 and 50 series are also offered in 409 stainless steel, while the Hushpower II mufflers are offered in either 409 stainless steel, or 304 stainless steel.

What pipe size should I use for a street application?
In general, the following guidelines should be applied for street applications.

2" tubing up to 100 hp per pipe
2.25" tubing up to 160 hp per pipe
2.5" tubing up to 200 hp per pipe
3" tubing up to 300 hp per pipe 
What is the difference between a 40 series and a 50 series muffler?
Both mufflers have the same sound outside the vehicle, but each has varying sound levels generated inside the vehicle. The 40 series (two chamber) will resonate inside the vehicle, generally around 1800-2000 rpms and also again around 2400-2600 rpms. The 50 series (three chamber) incorporates an H-chamber that helps eliminate this interior resonance in the cab area of your vehicle.

Will I lose power going from a 40 series to a 50 series, or to a 70 series?
No. Flowmaster engineers each series of mufflers for very low restriction with the main differences being varying sound levels both inside, and outside your vehicle. This way you can customize your vehicles sound levels to your vehicles needs and sound preference.

Do I need to install an "H" pipe to my dual exhaust?
Flowmaster strongly recommends using an "H" pipe, commonly known as a "balance tube" on all "true dual" exhaust systems. An "H" pipe equalizes the pressures between both banks of the engine giving a broader and flatter torque curve throughout the rpm range. It also eliminates "back-rap" common on deceleration, and creates a deeper mellower tone both inside and outside of the vehicle.

Is an "X" pipe better than and "H" pipe?
Over the years, Flowmaster's testing of all types of crossovers, including "X pipes", has revealed no substantial benefits over a properly installed "H" pipe on street driven applications. However, in race applications with small cubic inch engines and /or restricted (small bore) carburetors, will respond well to the addition of X pipes, tri-y styled collectors and/or properly designed single exhaust systems.

Will my late model vehicle run better if I replace the single inlet muffler with a true dual exhaust system?
Flowmaster does not recommend replacing factory single inlet exhaust systems with a "true dual" system on computer controlled vehicles. The computers in most late model vehicles will not be able to compensate with the fuel needed with an almost doubling of the exhaust flow. Flowmasters dual outlet kits will give you the look of a "true dual" system, while optimizing the vehicles performance.

Do I need to run tailpipes after the mufflers?
Yes, Flowmaster highly recommends running tailpipes out from under the vehicle. This directs the exhaust fumes away from the vehicle, while minimizing the sound transmitted into the cab area of the vehicle.

What kind of performance gains can I expect when installing Flowmasters on my vehicle?
Performance gains will vary dependent upon your application. The more power the vehicle makes, the bigger the gains will be. Generally, a 5-7% gain of power is fairly typical, while 1-2 mpg can be achieved. That is if you can keep your foot out of the gas to hear that Flowmaster sound.

How can I be sure that I'm buying a Flowmaster muffler?
The Flowmaster name is embossed in every muffler case that Flowmaster builds. If it doesn't say Flowmaster on the case, it's not a real Flowmaster muffler.


Flowmaster mufflers are designed to work with new or existing exhaust systems.  They offer slip on installation and can be welded or clamped into place.  Due to the use of heavier materials, Flowmaster recommends spot welding the joints when using clamps.  On some applications it will be necessary to cut or splice when adding Flowmaster mufflers to an existing exhaust system.

Lifetime Warranty SS / 3 Year Warranty Aluminum

Flowmaster is offering a lifetime limited warranty on their stainless steel 40 Series Delta Flow Mufflers and a 3 year limited warranty on the aluminum 40 Series Delta Flow Mufflers.