[gliding_serpent]

Q: What is this post?
A: The intent is to generate a community compiled resource on exhaust options and information (header/heat exchanger/muffler/cat bypass/etc) for the 911 3.2

How much does my exhaust weigh?

Power is a good thing, but weight loss can be just as valuable. Feel free to add any weight info you have on your exhaust components. If your numbers are different from posted, speak up, I will post a range of weights.

Stock HE's with cross-over: 46 lbs
Stock muffler: 25 lbs
SSIs: 31-32 lbs (thick flange, pair)
Gen 4 M&K 2 in 1 out: 16.5 lbs
Gen 5 M&K 2 in 1 out: ~15 lbs
M&K 1 in 1 out: 10 lbs
993 heat exchanger (Gillet): 12 lbs (11.91) ea. Total ~24 lbs

***Please contribute/correct and I will add to the list***

What does ____ exhaust sound like?

Check out the 17 pages and growing of exhaust videos until your heart is content. A word of reminder than an exhaust only sounds as good as the microphone recording it.
The ultimate exhaust sound clip thread!

How loud is ____ exhaust?

Here is a new thread with some subjective comparisons of exhaust combo volumes.
Is your exhaust too loud or too lame?

As you might realize, some people's idea of "loud" may differ based on opinion or hearing loss. I thought my exhaust was too loud at first, now I think it is just right. Mind you, I am sure may hearing is now irreversibly damaged from 1000miles of ownership.

"Decibel 10th" is a decent free app for measuring how loud your exhaust is. Do not worry, I am not affiliated. https://itunes.apple.com/ca/app/decibel-10th/id448155923?mt=8
I think readings like idle and 6K rpm while standing 3-5 feet from rear of the car would be most practical valuable.

- 1984 3.2 with cat bypass and custom bursch 944 sport muffler and stock interior and engine pad, iphone/app above to record: 90db idle and 101db 6k rpm at drivers seat. 100db idle standing a few feet from rear of car.
- 78 3.2 with SSI and M&K 2 to 1: At idle 800rpm (cold engine) average 84db peak 86db, at 3000rpm average drops a little to 82db peak 90db.
- 83 sc w SSI and M&K 2 to 1 and above app: idle dB was 91 dB and max stationery volume at about 6,000 RPM is 104 dB. (Note, a stock 3.0 will be quieter and not as deep as the 3.2)
- 3.2, Bursch 1 5/8 headers, M&K 2 into 1 out, Autothority chip: ~5feet away averaging 70dB at idle, +/-3 depending on what side of the car.

How much power can I expect form my exhaust upgrade?

This answer is not as straight forward as one might think.

Originally Posted by Bill Verburg

The header directs the flow of the exhaust gases, it's function is:
1. to contain the heat, hotter gas expands and flows faster
2. to direct the flow and keep the flow velocity as high as possible
3. to collect the flow from the separate cylinders in a way that doesn't introduce turbulence
4. to enhance acoustic reverberation that can be used to enhance cylinder filling and exhaustion

these functions are highly dependent on the geometry of the pipes and collectors, too big a pipe slows flow and allows the gas to cool too quickly, too small a pipe causes pressures to rise also inhibiting flow, too sharp a bend or poorly constructed transition introduces turbulence that slows flow, the length of the pipe and transition designs need to be correct to set up the standing waves used in acoustic tuning to enhance cylinder fill and evacuation.

a muffler on the other hand is designed to slow flow and absorb heat and acoustic energy, this is done by expansion, you want the largest/coolest volume to expand into(atmosphere is the best) and by absorption w/ packing material and by internal reflection.

A muffler can be designed for flow at the expense of acoustic modulation or vice versa, the bigger(editor's note: heavier) it is the better it can be at both, There are internal designs that can enhance one or the other property but rarely both.

Originally Posted by kach22i

Several examples and discussion in this old thread:
Custom Exhaust (Editor's note: this thread if full of great info on exhaust theory)

In general, dual cats and or dual mufflers are said to enhance top end rpm peak performance, while longer header pipe runs and combined exhaust via muffler mixing chamber increases low end torque and street-ability.

In that link someone managed to combine long headers with dual mufflers, then mixed the flows near the end, one of my favorites.

In fact if I recall correctly, there is even an example with electric by-pass baffles for top end performance, which close up and take a longer path to enhance low end performance.

Furthermore, gains (or losses) can be had with a simple bolt-on, but maximum gains come with a performance chip that is tuned to the the specific design aspects of the exhaust.

Originally Posted by Steve W

I've compiled a spreadsheet of expected power output values based on a internally stock 3.2 Carrera motor based on dyno tuning data that I've accumulated from many cars over the years. The output values are given in engine flywheel hp assuming a Superflow engine dyno such as at Jerry Woods. You results may vary, based on the flow quality of your muffler, but for a healthy 3.2 motor, I estimate these values to be accurate to within 2-3 hp of each other.

Editor's Note: Your car may vary. The above (stock power) figures appear to be for 1987-1989 US 3.2's. 84-86 vs 87-89 cars get the same end hp gains from chip/exhaust upgrades, even though the earlier cars start with less hp. Remember, the early cars had less hp due to chip programming only, so there is more to gain from an aftermarket performance chip.

ROW cars: less restrictive cat, 10.8:1 compression pistons, presumed different stock chip.
- 1984-89: 231hp. Their cat was less restrictive and is a popular upgrade for US cars.

US cars: 9.5:1 compression pistons. Stricter emissions also resulted in more conservative chip programming, and a more restrictive cat for US cars. The result = less power.
- 1984-86 California: 200hp. There is an extra "emissions brain" box under the drivers seat. Disconnect the brown wire for free 7hp.
- 1984-86 US: 207hp.
- 1987-89 California: ???
- 1987-89 US: 217hp. The 10hp gained was from revised chip programming. More power, same emissions.

Which exhaust setup?

For information on "Cat bypass/sport muffler" or SSI/sport muffler or "Headers/sport muffler" options, go here.

Originally Posted by JJ 911SC