Soul Performance

Hello Everyone,

My name is John Gaydos, and I’ve been an active Rennlist member and Porsche owner for many years while in the aftermarket performance industry. A few months ago I posted this thread in the 991 GT3 forum and it was very well received. As Porsche has been using the same center and side mufflers on the GT3 platform since the 997.1 generation (the only notable difference being the tip length/diameter), I've had a few requests from my 997 GT3 customers to post the information in the 997 GT3 forum as well.

I've seen a lot of threads weighing the differences between side muffler bypass pipes and center muffler bypasses exhausts and wanted to dive into the differences. Sound is very subjective - side muffler bypass pipes might meet your goals better than a center bypass, vice versa, or it just might be that a full header replacement would be a better match. Either way, an educated decision is the best decision so I’m going to get into the side muffler vs center muffler delete as that seems to be a popular topic.

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.
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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. Examples: " I LOVE" / "MY WIFE" or "MANUAL RULES" / "PDK DROOLS" or "PORSCHE" or "SMOKIES GT"



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.

Additional Weight and Heat Benefits: 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.
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LIFETIME WARRANTY: Enjoy your SOUL exhaust parts with confidence on both the street and track as they are covered by our Lifetime Warranty. Yes, we mean it...a full warranty for track use! Our team will quickly work with you to resolve any issues or answer any questions that you may have.
PACKING: We foam pack every product to ensure your components arrive in perfect condition.
CUSTOMER SERVICE: We are standing by to help in any way we can - pre sale and post sale, just let us know. No customer left behind, ever!

That all said, I invite any questions as an open/friendly discussion on this topic. We have some future GT3 products in the works and cars coming in for comparison videos. Until then I look forward to working with you!

Best Regards,

John Gaydos
Performance Specialist
PCA National Instructor

thxbuff2001

Do you recommend both together in a car your side valves bypass and center muffler bypass?

Hows the drone then

Jones3RS

This was a very informative write up. Thank you for sharing this!

Soul Performance

I'd run that setup all day long, though I'm also a track rat and accustomed to some cabin presence haha. The drone is present in cabin combining both the side and center muffler bypass pipes, and will be most prevalent in the low to mid 2000rpm range in high gear under load. Although this has the most "drone" factor of our exhaust combinations, I will say it is the most reasonable "straight pipe" system I've ever experienced on the GT3 platform across the 997-991 generation. This is due to our center muffler's expansion chamber design combined with the valves being able to route the exhaust through smaller diameter tubing diameter.

No problem, happy to spread a little education

Best regards,
John Gaydos

Steve Theodore

Extremely informative post, thank you John...it's great to see so much detail paid to what these modifications amount to. Although I bought a center exhaust bypass pipe from one of your competitors years ago, I've long wondered about the side mufflers and your post de-mystifies that very nicely. I appreciate it.

Soul Performance

I appreciate the kind words Steve, it was fun to finally do a deep dive and put my thoughts into a writeup haha. I see you are Sharky equipped, give Alex my best regards the next time you chat with him

-John Gaydos

Soul Performance

Does anyone have any questions about our GT3 components or mods in general?

-Mike

bovien

Do you have any sound volume measurements of the different combinations? CMB is an issue at many EU tracks, so I could be interested in testing out valved SMB at some point, depending on dB levels

adi_d

Do you guys made sports (200 CEL cats) or race headers (no cats) for the 997 platform or is that more or less a dead market at this stage?

Soul Performance

I do not have any volume measurements, nor would I want to take them either. There are way too many variables at play that we can't control to make a repeatable dB measurement. Most crucially the distance of the measurement, the surrounding area, and the load/rpm the car is being recorded at. The worst thing I can think of is taking a measurement and having a customer of mine buy something based off that measurement and it being completely different at their track. I can tell you that our SMB is less in overall sound level than the CMB, and I have made bolt on resonated turndown tips for that 991s that should also fit the 997s to couple with SMBs on sound restricted tracks in an effort to save weight and make sound.

We do not. It's not quite that it's a dead market but any time you put headers on these GT3's there is a very high likelihood the factory cetner muffler will blow out the backside from the increased pressure. So then you have to buy a center bypass as well which most find is too loud, or you have to buy a stronger center muffler which most find is then too expensive of a setup. And for another 20-30hp that most aren't going to take full advantage of anyway, the car has plenty of git from the getgo. So, we're sticking to the side and center muffler bypass pipes. If you're looking for a performance advantage, the side muffler bypass pipes rid the car of 35lbs and a notable amount of heat soak to the rear tires...that alone is worth the investment and the cherry on top is the sound enhancement. If you do want headers, I'd be happy to discuss a few options for you that I would consider quality replacements and source them for you as well.

Best regards,
John Gaydos

bovien

Good answer.
How do the turn down tips avoid scratching the black OEM tips when they bolt on?

Soul Performance

Our resonated turndown tips replace the entire factory tip assembly, which is only held on by three nuts (13mm I believe). Should only take a few minutes to swap them back and forth with the factory tips. Here are a couple photos to help visualize it. They're also made with v band clamps to allow for easy and quick adjustment away from the sound recording equipment, given you know what side of the track it is on and they allow you to do so.

bovien

Yeah, they are a piece of cake to remove.
Interesting product. I'll check it out on your website

Soul Performance

I appreciate the consideration

Modena 1

I have a question. I k ow you offer the side muffler deletes with and without the valves.

I imagine there is a reason why Porsche put the valves in there in the first place...torque at lower rpm. Am I wrong? I'm surprised this point doesn't come up more when people discuss deleting side pipes or simply unplugging the valve units.

Ty