Factory Sports Exhaust - Help Please

Anyone have any experience of the factory sports exhaust? Great noise which cuts out at 25mph and then comes in at 50mph. My local dealer tells me it's connected to the speedo and it can't be adjusted. I'd prefer to keep it all normal until 50mph.

I'm not sure about a speedo connection but there is a vacuum operated valve that causes the change in sounds at certain rpm's. A very common way amongst auto manufacturers to make an exhaust louder at higher rpm's and keep the governments happy with in-city noise levels. I have heard the factory 996 sport exhaust and it is the best sounding of all. Don't expect any performance benefits, though.

The consensus from the reading I've done seems to indicate the factory sports exhaust can work one of two ways: 1) normal install, where the noise level is diminished between 25mph and 50mph via electronic controls of some sort. 2) "loud" all the time, because the sports exhaust actual exhaust plumbing (muffler, etc.) is installed, but the control connections are not made. I have no personal knowledge one way or the other, as I'm on the wait list to buy my 996. This is just a summary of what I've reading on mailing lists and web boards.

Chris is correct! By default (if you do not install the control stuff) the valves are open all the time. I do not find that offensive... but I also do not rev over 4000 in my neighborhood. I really like the sound... like the first Porsches I bought in the 70's. Frankly, I think you buy a Porsche as the ultimate sports car OR you buy it as a comfortable stylish sports car. I am in the ultimate sports car camp. Loren (99 996) [ 06-27-2001: Message edited by: Loren..99..996 ]

So does the install on the "control stuff" affect the airflow? Obviously if the airflows are affected then the back pressure is affected and thus the performance is affected. And I would imagine without the control stuff installed, where the flow is constantly "open" and "loud", then the car would have less back pressure and would accelerate slower (in low RPM's)...am I correct in saying that? I am not an expert, but by piecing together the advice and tips of others, I am arriving at this conclusion. Or does the exhaust affect performance at all? I've heard people say "no" and "yes", but honestly that may be subjective, and on top of that I don't know if these people have the "control stuff" installed.

the formal answer appears to be "no" the sport exhaust doesnt do anything measurable for performance, but those who have had experienced it say otherwise who knows!

An instructor at a PDE course once said that the sport exhaust does yield performance improvements. He had stock exhaust and sport exhaust 996s and the sport exhaust equipped cars had faster lap times. Porsche's official word is that it does not increase performance but some speculate that it is due to DOT/EPA certification.

OrisChrono , I think that your hypothesis that "the car would have less back pressure and would accelerate slower (in low RPM's)...", is very plausible. It makes a lot of sense. I know a lot of shops talk owners out of hooking up the valves. They tell them it takes another couple of hours (or more) labor. Many people have taken this advice without probably ever considering your point. Porsche definately went to a lot of work to add that system. Did they do it in order to give the bottom end a little more kick? I've seen devices similar in theory on karts. I bet the sport exhaust valves at PDE were hooked up. With this in mind, I could see how even though the sport exhaust may not provide any significant peak Hp gain, it may actually provide a gain lower in the powerband by mechanically restricting the exhaust. Of course this would make even more sense IF the valve was controlled by RPM and not by speed. That would be trick.

The vacuum actuated valve system exists solely because of European noise ordinances. Something about 25-40mph being the speed at which an exhaust can not exceed a certain sound level. It's the speed range of most residential areas.

BTW, you mentioned karts. The big factor there is whether or not the engine is a 2 stroke or a 4 stroke engine. A 2 stroke engine relies heavily on the design of the exhaust. You need to carefully design the exhaust to effect desired. High torque or high RPM. That's why they call them "tuned" pipes. The size, length and the rate at which it increases in size all affect performance on a 2 stroke pipe. The point where the pipe opens up and increases in diameter is the expansion chamber and helps to draw gases out of the motor while the narrowing portion of the pipe gives the motor the backpressure it needs. A 4 stroke engine of that size does not rely as much on the exhaust pipe design.