In a recent 911 magazine article one of the writers mentioned that many after market exhaust systems increase sound levels, but often cause a *reduction* in power. His claim was that Porsche had developed their systems to the point of a maximum free flowing level and that many aftermarket systems actually reduced the efficiency of the exhaust despite sounding faster.

On the surface this makes sense to me only because Porsche has an engineering and development team specifically for dialing in their exhaust systems and quite a bit of resources at hand.......so with some of the best minds in the business designing their exhausts systems why would they leave power on the table?

I know I have read on this forum before that perhaps some low range torque can be reduced with aftermarket systems, but all of the aftermarket exhaust manufacturers post dyno's showing an increase in hp and torque across the entire rev range.

I have my eye on two different systems and have been trying to decide which way to go, but increasing the sound of the car is only, IMO, beneficial if it, at least, comes with no reduction in power.

Thoughts? And if you manufacture a system (FabSpeed, RennSport-1, Sharkwerks, etc......) please chime in.

Thanks all.....

 

Porsche does have bright minds on payroll but they are instructed to use them within limits. The limits are set by costs. At the end of the day, Porsche's number one priority and corporate goal is profitability. They are an enterprise that must make profit by keeping costs down to the very reasonable minimum.

Regardless, I will be getting an aftermarket exhaust system soon. I need those black round tips on my white car.

Cheers!

 

Could one of the more technically minded people explain to me how increasing flow rate, thereby decrease back-pressure, would cause a reduction in power? Wouldn't increased pressure cause the engine to do more work to achieve the same results?

 

I agree with Alex. Although there are bright minds at Porsche, they are all working to maximize performance within production & cost efficiencies. That said, assuming that cost & production limitations are relaxed (they will never be removed for any company or manufacture who needs to be profitable), exhausts designed with less limitations should in theory gain performance over stock systems....

with that in mind, i have to say that there must also be rubbish exhausts made by some companies that are only out to maximize profits and hence may produce a sub-par product, and market it solely based on aesthetics and sound versus performance...

my 2 cents...

 

I'll see and raise these comments...
No doubt that they are well funded and very bright engineers. But they are not only constrained by costs, but they have to target the center of the distribution of targeted buyers - with respect to durability, noise levels, and costs (above). Louder exhausts are doubtlessly appealing to many on this forum, but we're not the 'center' of their intended audience but rather one or two sigma out there (some would say 'lunatic fringe') re our preferences and tradeoffs.
The author is misinformed, but the conclusion that Porsche must choose to provide the highest-performing solutions would also be incorrect.

 

touche~

as mass market as porsche can be, i must agree with you here...

that said, one would have to assume & hope that a spirit of maximizing performance w/in alloted constraints is what makes a porsche the type of sports car we want it to be... else we'd be driving something else...

 

Please remember to consider that overall TQ and HP may not change, but the curve of where across the RPM range it comes on, may. So, yeah, some systems may reduce TQ or HP at 2,500 RPM's, but increase it at 6,500 RPM's.

It's all a trade off.

What I can tell you is that AWE Sport Cats most definitely increase power across the RPM spectrum. They also add sound.

If I had to to do all over again I'd do the AWE cats first, and if I still wanted more sound I'd change the mufflers. As is, I have AWE cats with AH mufflers, and it's as loud as a cup car- sort of over the top, actually.

My point is: if you want to add power and sound, go for the AWE cats first, and if you still want more sound, THEN add mufflers.
CATTMAN

 

BRANDX: where did you read this?

 

You may want to search the archives for something relating to exhaust and torque. I have read similar information that a great many after market products of all kinds, exhausts included, often add more noise, glitz or bragging rights but little in the way of usable HP and torque. And for my money HP way up the RPM range is of little use in real world driving. Short of super charging or adding NOS to a NA engine there isn't much you can do to significantly increase it's output without making major changes to it IE.. larger bore and stroke, bigger pistons, etc...Any bolt on claiming HP and torque increases across the RPM range is BS based on everything I've read on this and every other forum. Trust me. if it could be done Porsche would do it themselves and then charge everyone more than it was worth to buy it.

 

The best way to figure out if there's a gain is to do a before and after dyno at the same location at the day of the installation.

 

Interesting thread here and would love to chime in.
I don't understand all the physics of exhausts, but if you increase the flow efficiency it seems to have the biggest impact when the exhaust flows the most gasses, hence an increase in power at the top end of the band. To seek the most power and torque, you sacrafice low end power. Look at the peak of the sport - a Formula 1 engine. Horrible idle, no low end power, but peak power and torque at 19k RPM. It is VERY difficult to increase power across the whole band, but it is certainly possible. Indeed look at forced induction. But even turbos will often increase top end power and sacrafice the lower end.

On Porsche and exhausts - this is very simple. Just search for the pics of the stock 997 S headers and the factory X51. Very plain to see that costs were kept low to make the stock 997 S headers. Besides costs, the engineers need to "dial in" the final HP of every car. The 997 HP should be X, the 997 S HP should be Y and the 997 TT should be Z. So maybe the S doesn't have the most efficient headers. Look at the 997 headers - they are actually better designed than the 997S headers! Seems like depending on how the power is "dialed in", there are more or less gains to be had through modding.

 

Yes, but the point is an exhaust should NOT lose power at any RPM range - no exception.

 

I would agree with that. It is a crappy design if you actually LOSE power at some part of the range. However, gains are likely to occur only at certain parts of the band. And it wouldn't be that surprising if some designs provided max increase at redline, yet showed small power losses at the lower end.

 

Here's a great post on another forum that attempts to explain the physics behind backpressure and low end torque.

 

More on back pressure.