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Flowmonster Performance Muffler 3 inch dual inlet & outlet 12599-FM 409 Stainles

Flowmonster Performance Muffler 3 inch dual inlet & outlet 12599-FM 409 Stainles

SKU: 12599-FM
Regular price $86.14 USD
Regular price Sale price $86.14 USD
Sale Sold out

Unleash your Monster with Flowmonster 409 Stainless Steel performance mufflers! The Flowmonster series of absorption style mufflers deliver a moderate tone for the enthusiast looking for a deeper, more aggressive exhaust note than most OE (Original Equipment) mufflers, unlike the racey exhaust note associated with "chambered" style mufflers. Interior construction features 3.50 inch "straight-through" perforated 409 stainless steel tube surrounded by high-temperature sound absorption packing material which helps to deliver a deeper, mellower exhaust note. The internal design is reversible allowing the flexibility to be installed in either direction to best accommodate fitment with the intended vehicle. The fully MIG-welded 409 Stainless Steel material is embossed with the "FLOWMONSTER" logo on the case.
  • 409 Stainless Steel construction for superior corrosion resistance and good looks
  • Interior construction features high-temp interior sound absorption material delivering a deeper, mellow exhaust tone
  • Perforated High-Flow straight-through tube design for increased exhaust flow
  • Moderate increase in interior tone over most OE mufflers
  • A stainless steel performance muffler at an economical price
  • Internal Design is reversible allowing flexibility to be installed in either direction
  • Sold Individually
Automotive Item Grade High Performance
Brand Flowmonster
Color Stainless Steel
Emission Code 5
Finish Natural
Inlet Connection Type Clamp
Inlet Diameter (in) 3
Inlet Position Dual
Inlet Qty 2
Material Stainless Steel
Muffler Body Height/Thickness 5
Muffler Body Length (in) 22
Muffler Body Shape Oval
Muffler Body Width (in) 11
Muffler Inlet Diameter (in) 3
Muffler Outlet Diameter (in) 3
Muffler Series Flowmonster
Muffler Type Absorption
Outlet Connection Type Clamp
Outlet Diameter (in) 3
Outlet Position Dual
Outlet Qty 2
Product Type Muffler
Sound Level Moderate Sound
Type of Muffler Absorption
California Proposition 65 Required Yes
Part Number 12599-FM
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Policies and FAQs

Return Policy

We offer 30 days return of 100% purchase price for defective items. Return shipping and handling charges are the customers responsibility unless it is our mistake. (If shipping was included it will be deducted from the return)  If the part is wrong or defective please advise us if you would like an exchange, replacement or refund. We suggest our buyers keep tracking number delivery confirmation, and pack item securely to protect the return. If the part is lost we are unable to offer a refund. The part(s) must be returned in its original condition. Returns over 30 days may be accepted at a discounted price & offered store credit. Our return address is 774 Broad St Wadsworth, Oh 44281.


This is the line that runs from the front of the vehicle to the rear. On most vehicles it connects to a junction then you will have rear axle lines. On a few cars the intermediate lines will connect to the rear wheels. It is recommended to change the axle lines if you are replacing the intermediate lines.

Our kits include all of the solid metal lines for that section of the vehicle.

We are happy to help! Please help us to help you by going to our return form and filling out the form as best as you can in order to request a return.

  • Modern Day stands by our parts and is happy to accept returns within 30 days of purchase. Parts must be in new condition.
  • If a part arrives damaged, or is defective, Please report it to us immediately. So we can handle it for your promptly.

Yes but you will need to order in advance. All of our items are not stocked at our location. So please place your order online and we will notify you when it is ready for pick up.

Unfortunately we cannot offer single lines outside of kits

Yes, all are covered by the manufacturer's standard warranty. Most warranties cover the cost of parts. Any installation or other fees are non-refundable.

Online we accept PayPal and all major Credit Cards. If your are picking an item up we gladly accept cash.

We can only ship to your confirmed address in PayPal or your billing address if you pay with a credit card.

Orders typically Arrive within 3 to 10 days depending if it is a stocked item or something we have manufactured at time of sale.

Yes please send us a message through our custom orders page.

Yes, but items sent out of the continental U.S. may incur additional charges based on their destination

The left and right sides on a vehicle are determined as though you were sitting in the driver's seat. The left is the driver's side, and the right is the passenger's side.

Check it again tomorrow. It takes up to 1 day for the carrier to give status and a delivery date. UPS and FedEx provide delivery dates, USPS usually does not but they take no longer than 5 business days.

Yes! Thank you for your military service!

Still have a question or concern?  Please contact use our contact us form!

Yes! Thank you for your military service!

Warranty Information

Customer service is our top priority and because we value your time and energy we ask you to visit our Contact Us page and reach out so that we may assist you in finding the correct warranty for your product. Please include your name, the name on the order, the order number, and the SKU of the product to ensure the quickest and most accurate response to your inquiry.

Product Notices

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Customer Reviews

Based on 1 review
Auric.R Bischoff
Monster muffler

After a lot of asking , finally got a invoice that can be used for customs ,wished that they understood me earlier,but i finally got it thru customs and had to pay 111.50 dollar for shipping overseas so it was not cheap to get it , but super happy has an awesome sound and hope this will last a while before all the fiber cloth burns out in the exhaust , time will tell