Mwahaha, I finally found an aftermarket part that does just that. Its a butterfly valve that you attach to your exhaust(as far back as possible for best efficiency) that opens and closes to adjust the PSI of backpressure(or exhaust pressure whatever) to keep the volume and rapsyness down in aftermarket exhausts. It doesnt say in the article but it seems to me that some low end torque amy be gained by kepping the velocity of the gasses up. Here it is, its in aussieland
http://www.autospeed.com/A_0883/viewarticle.html Its kinda expensive since its not mas produced, but I think I can make a mechanical version of it easy enough!

No one has anything to say about it?

sounds cool but a complete waste of money imho...he has a good idea there but a lot of exhausts arent too loud anyways.

makes sense to me, the thing that counts the most is exhuast velocity. That's where you get that "An engine should have backpressure and etc.... " stuff.. hehe THat'd help spool up time a bit for really low comp engine too :)

<Hears "Backpressure" and explodes> "VELOCITY!!!!!" <still beet red>
-=B-= :D

I don't think plugging the exhaust with a butterfly valve is going to help anything (except sound). Changing the diameter of the pipe can have a positive effect on the power curve. But that involves picking the right size piping for the application. Adding a restriction is not going to help. I've seen this item advertised in SCC and can't believe that anyone would buy it.


Corbin

'95 ESI-T
HRC+FMIC+ETC...



Gimme fuel...Gimme fire...Gimme that which I desire

Haha, I only used backpressure cause they did. Breathe! I wasnt sure if it would gain power or not, just seemed it would almost duplicate smaller piping. On a similar note, with my dual size and outlet exhaust idea if there is a Greddy header and high flow cat before lets say 1.8in piping, will it affect the way the 1.8in piping alters the power curve? (I cant really explain that better right now) Also are there 3 position selenoids? TIA

Thank you, it’s a good thing we have some intelligent people on this board. I hate hearing about this backpressure nonsense. It’s all about gas velocity. When I interned with Delphi many of the myths of performance where beaten out of my head rather quickly. There were some true automotive nuts working there. That thing will do nothing in terms of performance. It will quiet the car down though, but at the cost of performance. And why will it quiet the exhaust down? Not because of backpressure! What will happen is a pressure wave will be reflected off the butterfly valve that is 180 degrees out of phase and all you Audiophiles know what happens then. The waves cancel each other out.

And if anyone wants to pick up some serious books about automotive engineering and not some comic book about engines go to SAE.org and get anything off their bookstore