Carbone Active Bypass Muffler

[Samcox912]

Has anyone used the CarBone Active Bypass Muffler? I have a 2.8L MFI that needs a new muffler and I've previously used Scart, but I'm open for change. Anyone have any live use of the CarBone?

Here is the link: https://www.carbone.pl/en/products/carbone-active-bypass-muffler-5051

[David Inc.]

Don't really like that it's two separate mufflers and it goes full straight pipe when open. That won't be something you could really use on the street without earplugs and might have lower frequency harmonics with them being separate.

[JonT]

isn’t that the point of having an active bypass muffler?

I’m waiting for the 3.6 model to be available

[David Inc.]

I guess, but I wouldn't want anything that goes full straight pipe. Like street and sport, but not street and god damn it where did I put my ear plugs?

I've driven a straight piped 911 down the road and it sucks.

[Bill Verburg]

a buddy has a GT3 muffler on his Roth sport 993 4.0, sounds terrificc in bothe modes

[JonT]

Originally Posted by David Inc.

I guess, but I wouldn't want anything that goes full straight pipe. Like street and sport, but not street and god damn it where did I put my ear plugs?

I've driven a straight piped 911 down the road and it sucks.

Lol I don’t doubt that!

[SkunkWorks]

I feel the M&K active system is proven and a better value, no?

[Showdown]

I have an M&K active bypass 2 in-2 out setup- I swapped the vacuum valves with electric valves so I can control when they open and I have to say the options are loud and LOUD AF. kind a bummer that there really isn’t any mild option.

[David Inc.]

Originally Posted by Bill Verburg

a buddy has a GT3 muffler on his Roth sport 993 4.0, sounds terrificc in bothe modes

Exactly, you still have to have some muffler on the bypass portion or it's just obnoxious. I have a Dansk GT3 style 2-in-2-out for my SC and I think it's about where noise should be on the bypass side. Any louder and no thanks.

[RarlyL8]

We've had an active exhaust option muffler for a few years now. The muffler is based on our Street mufflers with bypass valves added resulting in a Sport sound level when the engine is under load. Our Street mufflers were designed to meet California and European sound ordinance levels with idle and cruise coming in at about 72dB and 78dB respectively. Full throttle (valves open) ramps up to around 97dB by redline.

[rswannabe]

I don’t like that the Carbone exhaust does not appear to have any crossover between the left and and right cylinder banks. My understanding is that 911 motors benefit from a crossover connection that results in increased midrange. You want that on a street motor.

[Bill Verburg]

Originally Posted by rswannabe

I don’t like that the Carbone exhaust does not appear to have any crossover between the left and and right cylinder banks. My understanding is that 911 motors benefit from a crossover connection that results in increased midrange. You want that on a street motor.

au contraire

9111 6 is an even fire engine, there is an exhaust pulse every 120° of crank rotation , a pulse to each collector every 240°, w/ a very nice vacuum between them sucking the next one along.

top all 4 cycle events
bottom just the exhaust


when the pipes are kept separate there is a natural suction and additional acoustics that enhance flow at a specific rpm when the pipes geometry is correct. Connect the sides and that all goes out the window. You can see it on a dyno, where the connected sides introduce a pulsation in the torque curve. The sole benefit and the reason it's often done is noise abate ment and amelioration.


The myth of benefit come from US 90° V8s w/ 90° crossline cranks which are odd fire.

Odd fire engines have 2 cylinders consecutively fire on each back, this overloads the collectors periodically and gives them their distinctive sound.



odd fire Chevrolet LS




Thats the big deal w/ the Ford Voodoo V8, while 90° block the crank is a flat plane or 180° , making it evn fire


or the old Ford Gt40s w/ bundle of snakes headers, that while 90/90 routed the offending cylinders pipes to the other side, making the exhaust even fire.

Porsche ran into similar issues when they ran flat 8s

here are 3 3 versions of that type 771 engine

[pampadori]

Yes, my midrange is much stronger when I have each bank going thru its own pipe. swapping back to the 2 in 1 out BBE muffler i immediately felt a drop in power below 4500 or so. However, less vibration and noise is worth it for me right now.
I'm sure i'll switch back when the mood strikes.

[tk32]

Bill: do you offer courses on 911 suspension, exhaust, and wheel / tire combinations?

If so: sign me up... my mind is blown every time you post a chart or graph I have not seen before. 1/2 the time I am not even sure how to properly interpret the data, hence the need to enter into some schooling

[David Inc.]

Man I think what I really want is a 6-1 header to make the screamiest 911 I can.

[rswannabe]

I stand corrected and better informed. “Thank you sir! May I have another!“

Bill, that was as thorough an educational beatdown as I could hope to endure. With graphs even! From you I could expect no less. Thank you for your continued great contributions.

[Bill Verburg]

Originally Posted by David Inc.

Man I think what I really want is a 6-1 header to make the screamiest 911 I can.

No Porsche factory race car has used 6 -1 but privateers have experimented. BMW typically run 3-2-1, aka tri Y setups but they have tons of real estate do it. The trick is getting all the lengths and diameters and merges right.

Here is a Cox 3-2-1





The benefit of the tri-y's is a broader torque curve at the expense of max hp over a narrower rev range.

The other thing to keep in mind is that with mufflers and smog cams it's almost all moot anyway.

[David Inc.]

Oh yeah I would expect a performance hit from a 6-1 collector, it would just be for the wild sound.

Well heck, looks like someone makes a set, I'd love to hear what they sound like.

https://celeritech.nl/portfolio-items/porsche-964-headers-only/

[fanaudical]

Thanks for that great explanation, Bill!

[Bill Verburg]

Originally Posted by David Inc.

Oh yeah I would expect a performance hit from a 6-1 collector, it would just be for the wild sound.

Well heck, looks like someone makes a set, I'd love to hear what they sound like.

https://celeritech.nl/portfolio-items/porsche-964-headers-only/

I don't know that the sound will be any different and as far as I know, No One! uses a 6-1 that I have ever seen. They all use a variation of the tri-Y

surprised to see that Swiss version