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Old 01-05-2011, 08:01 AM   #1
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exhaust / cutouts / variocam

hi folks, got a question. in all the reviews i've read, dynos i've seen, etc., i've come to the understanding that the stock porsche exhaust is tuned (unequal pipes, specific back pressure) for low rpm power (better driveability). most aftermarket exhausts (equal pipes, less restriction) are tuned for high rpm power (big hp #s sell cars, but dynos all show power LOSS in the 2500 rpm area).

i also note that the stock intake is designed for both low and high rpm power - the variocam switches over, as well the resonance flappers on the intake manifold and plenum, as rpm climbs. the control of these is a combination of vacuum and ecu/rpm.

would it be possible to design an exhaust cutout that was either ecu/rpm or vacuum controlled that would drop the second cats and mufflers and go to straight pipes at the same time that the intake switched over to 'high rpm' mode? would it be as simple as using the same vacuum lines that drive the intake resonance flappers to drive a vacuum-operated exhaust cutout valve?

that way no need for expensive mufflers, midpipes, headers; just a cut-out that installs between the headers and the mid-pipe?

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Old 01-05-2011, 02:13 PM   #2
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ok, answered my own question (kinda). capristo make a muffler that does the job. the capristo muffler attaches to the mid pipes and has a bypass valve actuated by exhaust backpressure. backpressure builds (ie, rpm climbs) and the valve opens and bypasses the muffler. very cool, keeps the cats in the system (unless you delete them too).

similarly, porsche makes a muffler (the pse system) that uses the resonance flap vacuum as well as ecu control.

but they're also $2300 (pse) or $3500 (capristo)!!! now they both come with lectronics that allow to to control bypass valve operation, but i'm still sure you could do it with two valves and a vacuum switch for a lot less ...

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Old 01-09-2011, 08:29 PM   #3
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I have a by-pass modified OEM muffler which physically limits flow into the muffler. As the flow rate increases more and more gas volume is force out the by-pass route as turbulence starts to block up the entry into the muffler. This is the theory anyway. I have also dropped my secondary cats(fabspeeds) but still have the stock headers. It is hard to tell but I think I have lossed low end torque and of course all hell breaks loose above 4K.

The sound is truly amazing but can give you a false sense of performance.... I often wonder if I have hurt the performance of the car. Perhaps I have too little back pressure for proper scavenging in certain regimes.

Also wonder what ECU flash would work best with this set-up.
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Old 01-26-2011, 04:59 PM   #4
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Are you driving a 987? You might want to hear a Capristo in person before dropping the hefty sum of cash that that they cost. When in their quiet mode, the Capristo doesn't flow as well as the stock system, and in the loud mode they sounds like straight pipes. I know for sure that I'd get black flagged with a Capristo at my home track of Lime Rock, where they have sound restrictions.

I've had 3 different aftermaket catback exhaust systems on my car. I've had the Borla, the AWE Tuning and the SpeeedART. All of them delivered a noticable power increase, but each had its own sound personality.
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Old 01-26-2011, 06:02 PM   #5
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Virtually every aspect of the oem exhaust system is in some way restrictive . When you refer to the term "tuned", I don't think Porsche had performance in mind as much as they did keeping things OBDII compliant and Uncle Sugar off their back as far as emissions were concerned .
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Old 01-26-2011, 06:38 PM   #6
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Quote:
Originally Posted by Johnny Danger
Virtually every aspect of the oem exhaust system is in some way restrictive . When you refer to the term "tuned", I don't think Porsche had performance in mind as much as they did keeping things OBDII compliant and Uncle Sugar off their back as far as emissions were concerned .
But you'd be amazed at how well they work.. even when adding up to 400ccs of displacement via big bore hotrodding.

Not a single engine of mine received any aftermarket exhaust system in 2010... The data supports my decisions.
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Old 01-26-2011, 07:40 PM   #7
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Jake,

Are you saying keeping the entire stock exhaust system on a 2000 S is the best choice ?

I was thinking of eliminating the main cats and keeping the stock header with the built in cat. Or... would it be better to get a set of tuned headers and keep the main cats ?

Is there a loss in low end torque with either of these mod concepts ?
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Old 01-27-2011, 02:25 AM   #8
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Quote:
Originally Posted by Jake Raby
But you'd be amazed at how well they work.. even when adding up to 400ccs of displacement via big bore hotrodding.

Not a single engine of mine received any aftermarket exhaust system in 2010... The data supports my decisions.
Jake,

With all due respect, I experienced a marked improvement in performance over the oem system after I upgraded to a set of custom headers that utilized equal length primaries, a merge style collector, along with a set of 200 cell HJS tri-metal cats, to include deleting the secondary cats and replacing the oem muffler with a custom cat back exhaust. This led to a significant increase in horsepower/torque throughout the entire power spectrum as evidenced through dyno testing. However, there was a substantial price tag attached to all of this, and it involved two very well respected "tuners" in Germany - M&M Exhaust and 9FF. Prior to this, I experimented with all sorts of configurations. For example, deleting the pre-cats and leaving the secondary cats in place, and vice versa . Or, going completely catless and alternating between the oem muffler and an aftermarket catback; so forth and so on. In most cases, my vehicle lost low end and mid range torque. Moreover, all of these approaches proved to be futile in terms of reliability (keeping the vehicle OBDII compliant and avoiding CEL's ect..) and making strides toward better performance. It wasn't until the latter was accomplished that I achieved positive results . In any case, I'll concede that unless someone is willing to commit the time and money necessary to improve the oem system, things are best left intact. Still, I can't help but emphasize the overall restrictive nature of the oem system. Especially, the superfluous function of the secondary cats and the equally inefficient design of the oem headers/pre-cats.
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Old 01-27-2011, 03:13 AM   #9
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Quote:
Originally Posted by Jake Raby
But you'd be amazed at how well they work.. even when adding up to 400ccs of displacement via big bore hotrodding.

Not a single engine of mine received any aftermarket exhaust system in 2010... The data supports my decisions.
Perhaps the variables are different on your 996 and 986. On my 987, I did dyno testing before and after each of the three exhaust systems I installed. Each of them delivered about 15+ RWHP.

I changed the system more than 8 times, putting the stock exhaust back on between each install, in an attempt to cleanse my sonic pallette so I could best compare the new system to stock. The difference between the stock 987 exhaust and any of the aftermarket systems I tried was absolutely undeniable. In my experience, I didn't feel any difference down low, but from 5,000 up, the stock system just holds the car back. It's most noticable when you go back to stock after having driven the aftermarket for a while.

Believe me when I tell you, I'm not one of those guys that's going to tell you that my car felt so much faster after desnorking or performance air filter installation. I've tried those things and felt absolutely no difference. I'm a pessimist and it shows in my butt dyno.
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Old 01-27-2011, 06:51 AM   #10
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Originally Posted by Gator Bite
Perhaps the variables are different on your 996 and 986. On my 987, I did dyno testing before and after each of the three exhaust systems I installed. Each of them delivered about 15+ RWHP.

I changed the system more than 8 times, putting the stock exhaust back on between each install, in an attempt to cleanse my sonic pallette so I could best compare the new system to stock. The difference between the stock 987 exhaust and any of the aftermarket systems I tried was absolutely undeniable. In my experience, I didn't feel any difference down low, but from 5,000 up, the stock system just holds the car back. It's most noticable when you go back to stock after having driven the aftermarket for a while.

Believe me when I tell you, I'm not one of those guys that's going to tell you that my car felt so much faster after desnorking or performance air filter installation. I've tried those things and felt absolutely no difference. I'm a pessimist and it shows in my butt dyno.
Gator Bite,

I concur with your assessment. However, in the case of my vehicle, there was marked improvement in low end torque "right out of the chaulks".
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