IX XI

I follow this guy on YouTube as his videos are very informative. He recently posted a video regarding exhaust back pressure:

Doug H

It is more an issue of scavenging. Exhaust functions on pulses. Lower RMPs have larger gaps in the pulses and create pressure to pull the following pulse out the pipe like a drafting race car. The pulses get closer and almost instantaneous at high rpms. At low rpms or in the torque bands, you want a smaller diameter pipe to create more pressure and a larger pipe at high rpms to minimize pressure drop. Since you can only have only system, it is a compromise. You can go too free flowing to maximize peak hp, but it can reduce scavenging effect compromising lower end torque. Scavenging is comparable to creating vacuum pressure like race cars drafting off each other.

BillNye

Guy is kinda an idiot. He frequently over simplifies things to the point of being incorrect. And he's completely sold out to the clickbait titles and stuff (which is mostly a pet peeve).
Starting @2:40. Everything is compromises, some small amount of back pressure is a byproduct to improvements of other characteristics.

IX XI

Good replies, echoes how I understood it to work on these cars.

Doug H

The problem is terminology or semantics and efforts to over simplify. I did not watch the video, but he also may talking about cheaper cars where the exhaust systems are bunk and super restrictive. For the most part, exhaust systems on high end sports cars are pretty well tuned for all around performance so you can end up with trade-offs when trying to offer after market solutions.

Back in the day, I spent a whole lot of time on the dyno running cat bypasses, primary by passes, secondary bypasses and various combinations along with a stand alone fuel management system to try and optimize tune for each configuration. Learned a lot back then when tuning and setting up my various cars for street or track applications, but it has been a while.

Bruce In Philly

Some reads.......

https://motordyneengineering.com/exh...nd-scavenging/
http://www.hotrod.com/articles/engin...-inch-exhaust/

Peace
Bruce in Philly

ADias

The value of that video and this thread is to show that *****-nilly tinkering with exhausts may reduce performance.

IX XI

Bruce, thanks for the links. Very informative.

ADias, I tend to agree. Thus far the mods I've done are purely cosmetic (wheels, wheel spacers, exhaust tips), and all suspension related where I feel there is a real cost/performance benefit to be had (H&R springs, TPC DSC, GT3 sway bars and drop links, more aggressive alignment).

I've been thinking about getting an exhaust but not sure if there are improvements to be found that are worth the monetary investment or if I should stick with just mufflers for some sound improvement.

Frederic944

Petza914

This is one reason why the OEM PSE system when on Sport mode closes the valves when RPMs drop and then reopens them once they're higher again. Helps reduce one of the compromises with exhaust systems by supplying the higher back pressure at low RPMs for increased torque, and less restrictive at higher RPMs for increased flow and power, yet PSE owners continue to disconnect the vacuum actuator to prevent them from closing by themselves because they prefer the louder sound all of the time.

IX XI

Petza914

Fabspeed doesn't make their valvetronic exhaust for the 997.1 cars any longer (like what I have, and neither does Tubi), but I believe both FVD and cargraphic still offer a valved exhaust for the 997.1 that can be tied into the stock PSE controller or run from a remote (but then you probably lose the stock Porsche programming for the active open/close).

the_buch

Thanks all ... I learned a couple of things here I didn't know before.

Frederic944

For your information, the Porsche PSE has not benefits in term of performance, it has been designed and sold as just an enhancement for the sound, that's it.

And please, someone, please explain to us how back pressure can improve any torque at any RPM, more exhaust back pressure will just leave more burnt mixture in the cylinder, thus leading to decreasing the VE, how could it improve the performance? it just hurts performance! Now, if you talk about emissions, yes, having exhaust gas trapped in the cylinder will cool off the combustion and reduce Nox.

IX XI