Apexi PS exhaust

[Kracer427]

Just flipping through the April edition of SuperStreet and saw an ad for their new exhaust line, the PS. Thought it was some pretty inovative stuff. For those who haven't seen it, the muffler uses exhaust pressure to regulate a valve that will allow more/less flow. At low rpms, and low throttle the valve is shut and the exhaust gas must travel through a more restrictive and less noisey route. But when the valve senses high pressure, it opens to allow a straight through path for the gases to escape from. I don't know if this has been done before but i thought it was some pretty cool stuff, especially for the 95dB limit in cali. Props to Apexi

 

[whiteLS]

i think nissan uses sumthing like that in the spec-v

 

[Jeef]

I was actually thinking about this tonight. Tonight was the 3rd time I have driven the crx since I put the header on Sunday. I was thinking the lack of backpressure really sucks at low rpms. I used to be able to take corners in 3rd gear at slower speeds, and I had no problem accelerating afterwards. Now the car bogs a little. I was thinking it would be cool if there was some device that could adjust backpressure. Now someone has something out for it. I hope some people make it for domestics because I want to run a dual exhaust on my truck without losing any torque.

 

[JDMilan]

cool find.......news to me..

 

[E_SolSi]

BMW has been doing this for YEARS

 

[StyleTEG]

Originally posted by Jeef@Mar 18 2004, 09:25 PM
I was thinking the lack of backpressure really sucks at low rpms.  I used to be able to take corners in 3rd gear at slower speeds, and I had no problem accelerating afterwards.  Now the car bogs a little.  I was thinking it would be cool if there was some device that could adjust backpressure.

The necessity of backpressure is a very popular and common myth. Backpressure is always bad, it always reduces power.

Exhaust velocity is what is important. When you go to a larger pipe you lose backpressure and this is a good thing. However at lower rpms your engine does not create enough exhaust gases to keep at the velocity that it did with the smaller pipe. Think about a hose with water running through it, then pinch it off partially. The water comes out faster.

The problem with a smaller pipe of course, is at some point it becomes a bottleneck. So you end up with sacrificing low end power for more high end. A valve at the end of the muffler is not going to help this situation.

 

[v13tl2omeo408]

So i guess Japan is getting their ideas from Germany. Anyways, i think it is a great idea.

 

[xj0hnx]

Originally posted by StyleTEG+Mar 20 2004, 01:41 AM-->

Jeef

@Mar 18 2004, 09:25 PM
I was thinking the lack of backpressure really sucks at low rpms.  I used to be able to take corners in 3rd gear at slower speeds, and I had no problem accelerating afterwards.   Now the car bogs a little.  I was thinking it would be cool if there was some device that could adjust backpressure.

The necessity of backpressure is a very popular and common myth. Backpressure is always bad, it always reduces power.

Exhaust velocity is what is important. When you go to a larger pipe you lose backpressure and this is a good thing. However at lower rpms your engine does not create enough exhaust gases to keep at the velocity that it did with the smaller pipe. Think about a hose with water running through it, then pinch it off partially. The water comes out faster.

The problem with a smaller pipe of course, is at some point it becomes a bottleneck. So you end up with sacrificing low end power for more high end. A valve at the end of the muffler is not going to help this situation.

Back pressure bad, delta pressure good, but since delta pressure is the drop in pressure inbetween exhaust pulses (which cause backpressure as they try to get out) that helps pull spent exhaust out, you can't have one without the other. This all comes to the need for tuned headers with varing length/diameter runners and collectors that help use those pulses to get the exhaust out as fast and smoothly as possible.