TECH TALK: 911 GT3 Side Muffler Bypass vs Center Muffler Bypass

The GT3 exhaust design consists of three components (headers, side mufflers, center muffler) – the last two are often compared and considered as the best return on investment when it comes to mod time and cost – but which is the best solution for you?

You can see how much of a difference there is in sound restriction between valves open and valves closed. The distance the exhaust travels, the piping diameter, and the number/size of chambers and baffling it goes through all contribute to a restriction in sound level and cabin presence with valves closed, or a lack thereof in the valves open condition.

With valves closed, the factory side mufflers have a larger volume area, longer distance to travel, and a smaller 50mm tubing diameter in which to do it than the factory center muffler. With valves open, the factory side mufflers have a shorter distance to travel (air gap) between the 63mm entry pipe and exit pipe than the factory center muffler. This helps explain the differing sound characteristics between the side and center muffler deletes below. Most aftermarket CMB will forgo the factory chambered design for a straight through flow path, yielding the more aggressive exhaust note – like our design below.

Weight savings: 11 lbs
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Center Muffler Bypass exhausts (CMB) have a more raw, deep, aggressive exhaust note than side muffler bypass pipes. Regarding the cabin presence and overall sound level, they are typically quieter with valves closed, and louder with valves open. This also causes them to have a much more intense transition from the valves closed to open position. Some people do not like that aspect of the center muffler bypass. You can run a CMB and disable vacuum or control the factory valves with a valve controller to have the valves open at all times. Some CMB’s will allow you to change the tips as well.

Our CMB is a cost effective solution for a more aggressive sound with customizable tips for a unique look.Each system is made from mandrel-bent T304L stainless steel tubing. Mikalor Supra Heavy-Duty W4 Clamps are included to mount the system to the vehicle (also included to mount Single Wall tips). Projection welding spots, swinging bridge, high-strength stainless steel bolt and the exclusive design of the captive nut and trunnion offer superior clamping forces and longevity. AccuSeal clamps are included to connect the exhaust to the side mufflers. We offer a variety of exhaust tip options ranging from double wall tips to attractive single wall stainless steel tips. For 991 GT3 exhaust applications, we recommend 4″ tips to fill out the bumper, but 3.5″ tips are available by request. 991.2 GT3 tips are slightly longer as a result of the change in the bumper.

Yes, we do customization! For an additional cost, we have the ability to PVD coat these tips black AND if you want to support your business, if you want to support a cause, if you want to stand out….given there is space we have the ability to apply custom lettering/logos to the single wall tips.

Side Muffler Bypass pipes (SMB) are smoother and more exotic in pitch, akin to the factory exhaust note but uncorked and much livelier with a better tone. It is not quite as loud as a center muffler with valves open, and with valves closed it is not quite as quiet. However, it still has minimal drone characteristics due to routing the exhaust through the more restrictive top entry of the factory center muffler with valves closed. SMB’s also have a much smoother and less notable transition from valves closed to open vs a CMB. Also for reference, our non-valved SMB’s offer essentially the exact same sound as our valved SMB’s in the valves open position. Eliminating the valves saves an additional 3lbs which is ideal for more dedicated track cars that don’t need PSE functionality.

We utilize a dual inlet design for our side muffler bypass pipes that utilizes both the upper and lower entry to the center muffler. This bleeds off pressure into the top of the center muffler, more evenly distributing the pressure and promoting the life of the factory center muffler. We also utilize a flex pipe in the upper pipe to prevent fatigue and to allow for easier installation. We have yet to experience a factory center muffler fail when used with a dual entry side muffler bypass and factory headers, including dozens of GT3’s with thousands of track miles at Sebring during John Gaydos’ time building GT cars in Florida.


MSRP: $1,395
Weight savings: 35.4 lbs / 16 kg (44.9 lbs vs 9.5 lbs)
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Additional Weight and Heat Benefits of Side Muffler Bypass Pipes

Side muffler bypass pipes are an underrated modification, especially for track enthusiasts. Side muffler bypass pipes have two distinct advantages over a center muffler bypass from a performance perspective – weight and heat. A center muffler bypass saves around 10lbs of weight off the rear of the car while dual entry side muffler bypass pipes save about 35-38lbs depending on whether or not they contain valves. Side muffler bypass pipes also rid the car of a notable amount of heat soak just inches off the rear tires. This helps with more consistent / cooler tire temps at the track, especially if idling or warming up the car in the pits / paddock prior to going out for a session.


MSRP: $945
Weight savings: 38.3 lbs / 17.3 kg (44.9 lbs vs 6.6 lbs)
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If you have any questions about modding your GT3 – contact our experienced team and we’ll help you get the performance and sound you are looking for in your GT3.

Best Regards,

John Gaydos / Performance Specialist  –   Mike Spock / Marketing Manager