The ultimate exhaust resource for the 3.2 (under construction)

[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

[cashman]

This has a lot of information
The ultimate exhaust sound clip thread!

[TheSt|G]

I knew the SSI mistress photo was going to make its way in here.

[KTL]

I think this thread is going to be very difficult to maintain a truly accurate listing of what results are gained (or lost) from the exhaust swap. Reason I say that is because the vast majority of these people make the switch to a non-stock exhaust setup and don't properly re-tune the engine to account for the swap. So there should be two collections of samples- those who re-mapped the DME chip and those who didn't

[trader220]

Originally Posted by KTL

I think this thread is going to be very difficult to maintain a truly accurate listing of what results are gained (or lost) from the exhaust swap. Reason I say that is because the vast majority of these people make the switch to a non-stock exhaust setup and don't properly re-tune the engine to account for the swap. So there should be two collections of samples- those who re-mapped the DME chip and those who didn't

Just arrived yesterday is my brand new M&K GT3 Style 1 in 2 out muffler, M&K premuffler, Steve Wong 93 octian chip, set up for pre muffler and exhaust.

My assumption is that this is a straight bolt up chip in set up. Am I missing something that needs to be tuned to the new set up? 88 Carrera 3.2 bone stock otherwise.

Thanks

[gliding_serpent]

There are three main recipes when trying to maximize the power of an internally stock 3.2 engine. Your choice depends on your goals, and your budget.

In concept you are increasing the power output of the engine by allowing it to "breath" better. In stock internal form, the 3.2 is not felt to be intake limited (some claim a 1hp gain from intake drilling or aftermarket intakes... I argue that is the realm of error). Where the engine is limited is in gas exhaust. Design compromises were engineered into the exhaust system to meet strict noise and emissions regulations in the US. All exhaust "performance" upgrades center around the idea of optimizing exhaust gas exit velocity, back-pressure, and thus power. Another way to look at it, the faster your can channel away exhaust gasses, the more efficiently the engine can take in air and make power. This is a simplistic view, but will do for now.

Stock heat exchangers + cat bypass + "1 in" sport muffler+ performance chip

This is the most budget minded upgrade and is thus quite popular. Many call it the "low hanging fruit" and is good bang for the buck. It also keeps the stock heat exchangers which makes for less labor and keeps the car closer to original if that is your thing. It is generally felt that the stock heat exchangers are not the limiting factor in the exhaust. This combo sees most of it's power gains in the high rpm regions but gives the power-band an overall nudge in the right direction. The stock "1 in" exhaust design is maintained which is felt by some to have internal design flaws that limit full performance potential. Others will say it is an excellent (but heavy) design that can be easily modified for increased flow/power at a cost to noise.

SSI heat exchangers + "2 in" sports muffler + performance chip

SSI's are basically a reproduction of early 911 steel header/heat exchanger design, but made out of stainless steel for better durability. As of 2013 they are made by Dansk. They are 1 3/8 internal diameter (35mm) equal length 3:1 headers with heat exchangers. The exhaust route for each bank of 3 cylinders is kept separate (which is good for single phase motors) but will require a "2 in" muffler. For the 3.2 they have thicker exhaust flanges for proper clearance.

Although the internal diameter is said to be slightly "suboptimal" for a 3.2 engine (1.5 inches or 38mm is said to be ideal), performance gains are seen across the power band compared to stock (and catbypass/sport exhaust), and gains presumably come from equal length primaries, and separate cylinder bank routes (i.e. higher exhaust velocity). The strength of the SSI design is maximized in low/mid range rpm street driving where the smaller diameter primaries are ideal for keeping exhaust velocities optimal , adding hp, torque and drive-ability. SSIs give you a flatter torque curve, which gives you more initial grunt, but the high rpm power band gets less of a gain compared to larger headers. Smaller primaries shift the torque curve into the fill out the "lower" rpm, at a cost to the high rpm (reverse for larger primaries).

The high end rpm band is where SSIs seem to be more controversial in their benefits. The concept here is that as HP increases with high RPM, you have more exhaust gasses and more heat. This should produce faster exhaust velocity, but the issue is that the smaller primaries begin to be overloaded and back-pressure becomes excessive, effectively choking out the true potential of the engine. When someone says that "SSIs don't breathe well at high rpm," this is what they are referring to, if they understand the physics or not. If you look at Steve Wongs chart above, you can see that the SSI's still add top end power from stock, and even a touch more compared to a cat bypass/sport muffler, but they lack the high end power potential of the larger diameter headers. Power dips off pretty quickly above 6k rpm which is not really an issue if you keep stock redline. Larger diameter headers are still the high rpm power king and the choice for track cars. In a perfect world, as rpm increases the diameter of primaries would increase also, allowing perfect exhaust velocity at all times. In the intake side of things, that is how varioram operates.

So the SSI (with sport exhaust and matched performance chip) is a good match for a street focused driver that wants more power across the board, but additionally more usable midrange power.

Down sides include high cost (parts, instillation), minimal power gains over the cat bypass/sport muffler setup, and the hassle of fitting (risk of broken exhaust studs when removing the old heat exchangers. You must replace a couple oil pipes to accommodate the SSI's and risk ruining the thread on the thermostat. You need to modify or backdate your heating system). Finally, if you have a 915 gearbox you have to "massage" the edge of left SSI to clear the clutch helper spring.

Headers + "2in" sport muffler + performance chip

This is the clear choice for the track folks. They are generally designed to isolate right and left exhaust gas pathways (good for single phase engines) as long as possible, thus necessitating a "2 in" muffler similar to SSI setups. A well designed header system is light, and often has a larger internal diameter than stock (38mm or 1 1/2 to 1 5/8ths is felt to be ideal but opinions vary). Verify the internal diameters, as external diameters are often reported and the thickness of materials varies by manufacturer. As mentioned prior, a well designed header will have equal length primaries that minimize exhaust turbulence and maximize exhaust velocity. The best ones are also tuned to the resonance of the exhaust pulses. There is more to it than that, but further details can be left to others.

Dogma is that well designed longer primaries should promote mid range torque by optimizing back-pressure (porsche later switched to longer exhausts in the 3.6 cars for this reason). Keeping the left and right side exhaust separate helps high rpm power, at a cost to low/mid rpm power. A properly designed cross-over after the primaries (accomplished by a well designed "2 in" muffler) is also said to promote more ideal back-pressure and mid range performance. X-pipes are a point of debate that I will not get into.

The gains seen from SSI's are similar to those with larger headers, except that with smaller primaries, SSI's favor mid range power. As the diameter of primaries increase, the ideal power band gets shifted "right" to optimize high rpm gains. Where the smaller SSI's eventually get overloaded by the high volume of exhaust gas produced at high rpm, the larger diameter headers are just starting to stretch their legs. So bigger primaries are better right? Not really, or "it depends".

As exhaust gasses enter a larger chamber they cool, pressures drop, and the gas velocity decreases. This is a bad thing for low and mid rpm torque where the diameter of the primaries is not a limiting factor. In a way, the larger primaries become sub-ideal by reducing exhaust velocity at these low rpm's. There is a reason cars with an aggressive race exhaust can feel/run poorly at idle or low rpm. As rpm's increase, and the volume of exhaust gas increases (more combustion and more power) the larger primaries are better able to cope with the increased exhaust volume, and exhaust velocity is optimized. The engine is better able to "breath" at high rpm and the and the full power of the otherwise stock engine can be realized. Thus, if you look at Steve Wong's chart of expected performance gains (see post #1), you will see the larger header match-ups give the highest max hp. In theory, the larger the header diameter, the more power potential, and the higher the rpm you get this power. As a trade off, the mid-range power takes an increasingly large hit (and the exhaust becomes increasingly loud). Eventually, the power band becomes too high in the rpm range for an otherwise internally stock engine to reliably make use of. Thus, to make full use of the most aggressive exhaust systems you really need your redline increased, requiring internal work to make it reliable. To get the most out of the car you need to have it at or near 10/10th all the time. I like to call that a race car.

That being said, it you are doing internal upgrades to the engine (increasing power and exhaust flow needs) you can effectively make better use of the larger primary and "shift the power curve back to the right" into a more useful range. The more powerful the engine, the larger the exhaust you will need.

Final Thoughts:

1. Tuning is everything. Your performance chip needs to be programmed for your specific exhaust setup to full realize the gains. Also, not all headers/mufflers were created equal, and some combinations will work better for your needs.
2. Bigger primaries (and to a lesser degree louder free flowing exhausts) are not better, but they do enhance high rpm power at a cost to power down low. If your car lives near redline than your choice is obvious. If your car is concourse, your choice is obvious, and you laugh at folks like me who debate these "upgrades." If you want more useable power in "real world" situations, the SSI might be best. If you have a budget, the cat bypass system is the way to go.
3. The ideal exhaust system has primaries that increase in diameter as the power/rpm of the engine increases, and vice versa. If you can find this unicorn of an exhaust, please let me know. If it exists, I bet it costs a lot.
4. This is not gospel, and is open for debate/amendment.

[911pcars]

How much does my exhaust weigh?

We all know power is a good thing, but weight loss can be just as valuable. Feel free to add any weight info you may 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 lbs
Gen 4 M&K 2in/1out: 16.5 lbs

I posted this on yet another exhaust thread last week:

SSI (thick flange): 16 lbs each. Total: 32 lbs
993 heat exchanger (Gillet), 12 lbs (11.91) ea. Total ~24 lbs

Cost comparison
Note: The effort/cost to adapt either one depends can be a wash depending on the parts and fabrication skills/sublet labor required.

SSI on a '74-on 911:
Removal and sale of stock system; factor in potential damage to exist. cyl. head exh. studs
Fit early or aftermarket oil line: engine>oil tank
Adapt/backdate hot air components for cabin air
2 in/2out muffler
O2 Sensor harness extension

993 HE on 3.2 or earlier engine:
Removal and sale of stock system; factor in potential damage to exist. cyl. head exh.studs
"Flip"/Rotate (3) HE inlet flanges to match pass. side cyl. head exh. outlets
Adapt/fabricate/backdate hot air components for cabin air
Fabricate tubes and support mounts: HE > muffler > tailpipe
2 in/2out muffler
O2 Sensor harness extension

Sherwood

[Quicksilver]

The referenced chart of 3.2 performance should address the different performance levels of the early (84-86) and later Carreras (87-89).

--------------------------
I'm putting my B&B's back on the car this weekend so now would be a good time to weigh them...
But I don't have an accurate scale.

[KTL]

Anybody who's chosen to get a 911Chips replacement chip is on the right path. The ones i'm referring to are those that just change the exhaust because they want better breathing and nicer sound, but then don't see any gains in actual performance.

Ideally the best way to do it is to perform the modifications and then have the car dyno tuned. Then you have concrete evidence that the exhaust change was accommodated reasonably well by the ECU chip re-mapping. Given that Steve Wong has done just that with a lot of these cars, his "ballpark" tune that he puts in the chip is going to be good enough for most people.

[JJ 911SC]

Originally Posted by TheSt|G

I knew the SSI mistress photo was going to make its way in here.

I was surprise too when I saw it this morning. Wife still laughing at that one

[911pcars]

Originally Posted by KTL

Anybody who's chosen to get a 911Chips replacement chip is on the right path. The ones i'm referring to are those that just change the exhaust because they want better breathing and nicer sound, but then don't see any gains in actual performance.

Ideally the best way to do it is to perform the modifications and then have the car dyno tuned. Then you have concrete evidence that the exhaust change was accommodated reasonably well by the ECU chip re-mapping. Given that Steve Wong has done just that with a lot of these cars, his "ballpark" tune that he puts in the chip is going to be good enough for most people.

Yeah. the difficulty is in isolating and maximizing a single "upgrade" in order to determine its sole effect on engine performance. Steve W's chart describes a +6 gain using SSI over a stock factory exh. system. That's not exactly no gain, but it's not as dramatic an improvement as many would hope. However, like other upgrades, results improve when performed in concert with related upgrades (re-mapped chip, improved muffler, etc.).

Sherwood

[Pstallo]

trader220,

I would love to hear your opinion of the GT3 1-in 2-out muffler. I have the M&K premuffler and Wong chip and am considering the 2 out gt muffler (Brian at RarlyL8 lives a few miles from me).

How is the sound? I have the standard muffler and found the premuffler to be not much louder, but a bit 'growlier', a bit deeper. I love the look of the 2-out, but am worried that it may be TOO loud for the neighbors.

[michael lang]

This is really an interesting thread as I'm about to start putting my engine back together and am going with SSIs and sport muffler (not sure which one to go with but will find something that compliments everything I am doing with the rebuild) & 964 cams. Once I'm finished going back together then I'll chip the ECU to compliment everything that I've done. The chart above above only confirms in my mind that the plan I laid out for my rebuild will work in theory. Now it's just a matter of completing the reassembly.

[trader220]

Originally Posted by Pstallo

trader220,

I would love to hear your opinion of the GT3 1-in 2-out muffler. I have the M&K premuffler and Wong chip and am considering the 2 out gt muffler (Brian at RarlyL8 lives a few miles from me).

How is the sound? I have the standard muffler and found the premuffler to be not much louder, but a bit 'growlier', a bit deeper. I love the look of the 2-out, but am worried that it may be TOO loud for the neighbors.

I hope to get to the install on Sunday but odds are I wont be done until sometime next week. I'll keep you posted.

[gliding_serpent]

Originally Posted by 911pcars

Yeah. the difficulty is in isolating and maximizing a single "upgrade" in order to determine its sole effect on engine performance. Steve W's chart describes a +6 gain using SSI over a stock factory exh. system. That's not exactly no gain, but it's not as dramatic an improvement as many would hope. However, like other upgrades, results improve when performed in concert with related upgrades (re-mapped chip, improved muffler, etc.).

Sherwood

Not a huge jump for sure. What the chart lacks however is torque, which would add to the value of his chart further.

Looking at the data, when to comes to bolt-ons, most power comes from the re-mapped chip. Exhaust factors in a bit when you allow it to breath, however the high HP gains come at a cost to mid range torque, so after a point it becomes less of an overall gain, and more of a trade-off. Sound becomes a huge factor in that trade-off also.

[gliding_serpent]

some very good discussions on exhaust and header theory. This site is full of great info.

Mufflers - "one size fits all"?

[trader220]

The M&K GT3 1 in 2 out along with pre muffler is installed. I still have to trim and paint the new rear valance. Steve Wong Chip in too. My thanks to Kevin over at The Porsche Specialist in Broomall PA.

Its not nearly as loud as I had figured. Does have the baffles in. Its got a nice deep sound at idle and it opens up but not obnoxious over 3500/4000 revs.

I was hoping for a bit more seat of the pants power. The sound is clearly different and better but its not all that noticeable in performance on the first drive. Its supposed to be nice this weekend I'll get some more time behind the wheel and try and get a sound clip.

Here is a picture or two:

[gliding_serpent]

Looks great. If the steve wong chart is to be learned from, the muffler itself has a smaller influence on power than the header design, which has less benefit than the chip itself.

[RarlyL8]

When you change out the cat and muffler on a 3.2L you need to change the chip as well to re-tune the fuel system so the exhaust can be optimized. Because of this it is hard to say how much effect one or the other has as they work best together. A proper baseline would be to chip the bone stock engine then change the exhaust and re-chip. I'm sure Steve has that information.

[gliding_serpent]

a couple more good threads

Sneak Peek of New Stainless Steel Headers

The ssi vs 1 5/8 header dyno comparo is interesting, especially Steve Wong's views on page 2.

3.2 Headers

opinions on header sizes. 1 1/2 internal diameter seems to be the sweet spot. Exhaust/Header Size 3.2 Carrera