tron1

What can be the negative result of reducing exhaust backparessure? Can a high performance muffler which reduces backpressure 50-75% be detrimental to the engine? valve train? intake system or....? I would be very interested in comments regarding the S2000. Thanks in advance.

Road Rage

Nothing. No. No.

Exhaust backpressure is one of the most misunderstood concepts on the Internet. When i have some time I will post a full physical analysis. While running with a broken exhaust manifold could damage a valve, I no one no aftermarket exhaust which could cause a problem.

Besides, the stock system is excellent - people replace it for weight savings and a sportier note, but large HP gains simply are not to be found in this car from exhaust mods - even a header and CB produce only 1 or 2 handfuls.

SSS2k

Backpressure is always bad. The less BP the better, but what you dont want is crappy exhaust flow consistency. You must walk to fine line of having a large enough pipe to reduce BP to a minimum, but not large enough that you lose the harmonic flow of exhaust that the engine needs.

mikecl713

backpressure increases torque right? u need a lil back pressure

svatne

I replaced the stock S2000 mufflers on my '03 Suzuka Blue with straight through Magnaflow Racing series polished stainless steal mufflers of the same length and internal pipe diameter (as stock). THey are much lighter, smaller external diameter, look nice, and sound great - very, very deep sound. Rather amazing for a four cylinder in fact. Feels like a little snappier throttle response, too, although that maybe placebo. Maybe Tron1 can post a picture or two, since I cant.

Uncle Fester

No, backpressure does not increase torque.

The function of the exhaust is to simply route exhaust gases where they can be safely emitted from the vehicle. The exhaust must route the flow of gasses whether the car is at idle, or if the engine is running at redline. Obviously, the exhaust must accomodate a larger volume of gas when an engine is redlining vs. an engine just idling.

Exhaust leaves the engine in pulses travelling nearly at the speed of sound! Keeping these pulses going as fast as they can is ideally what you want (gas flow velocity). However, exhaust piping has a fixed diameter, and can therefore flow a certain amount of gas volume up to a point.

Imagine placing an exhaust with a 1" I.D. on an S2000. You might actually see a little bump in torque down low, but only because the amount of exhaust flow at that particular part of the rev band flows very well through 1" piping (even better than the stock piping). But at 8000 RPM, the 1" pipe would be quickly overwhelmed and you will lose a lot of power.

SSS2k hit the nail right on the head with his post. You have to select the right size piping according to the engine's characteristics. The F20C will produce a large volume of exhaust gas when revving to 9000 RPM, so the Honda engineers sized the piping according to this. If you go with too large of a pipe diameter, then you never achieve optimum exhaust gas velocity, and you will lose power. Going too small will give you the scenario I mentioned above.

Now exhaust tuning is more than just pipe diameter. You have to consider thermal effects, and like SSS2k said, even harmonics play a part. Hopefully this helps.

l8brakr

Since our motors have charateristics similar to the two wheeled variety has anybody experimented with variable exhaust flow? If your not familiar most of the openclass sportbikes now have some kind of valve or sylenoid that regulates exhaust gasses at different rpm's. I haven't had my car for long but am planning on having a custom exhaust fabricated. It wouldn't be all that difficult to develop an insert near the Y at the rear axle that could open and shut at predetermined rpm windows sending exhaust through a single pipe or through both thus varying the flow charateristics to match the optimal scenario. Does this sound like it could be benefitial? Or does anybody know of someone that has already attempted something similar? Any ideas are welcome!!

Road Rage

I have to say, the responses in this thread have been some of the most thoughtful and accurate I have ever seen on a web Forum. I think it speaks well of the posters, and this Forum. Nice job, gentlemen!

Some BMW's have an electrically controlled exhaust valve in the muffler. Euro laws on pass-by noise are very strict, and I thnik the BMW system opens the exhaust at WOT to regain some ponies lost to the sound police.

I think the motorcycle comparison may be hard to hold, since they rev so much higher, and the flow dynamics likely get more complicated at those engine speeds - I will have to ponder that one.

I wonder if they allow this in F1?

KaNgArOo

Sooooooo....what is a good size pipe to give our cars the best performance.....I know single exhaust are better...but i have a dual.
I currently have Tanabe racing medallion...i think it is 60mm piping all the way to the cat...and dual 4 inch cannons..
yea there big but i like the looks..

SSS2k

The tip size doesnt really effect the flow of the gases, not sure what 60mm translates to but for the S Im guessing that 2.75 inch piping would be pretty good.