Let's say you have identical exhaust systems except for one has a resonator in place of the test pipe. Is there a power loss with the resonated exhaust? It seems like the pulses would expand in the resonator, cool off, slow down, add turbulence, re-compress, and move slowly down the stream; Thus killing vacuum between pulses and their effects on subsequent pulses.

Maybe I'm thinking too much about it

 

Yeah I doubt you would see a difference, maybe .5-1hp difference with a resonated system. I think you would lose more power to heat soaking the intercooler than a resonator. Resonators make many exhaust systems sound much better and not raspy also eliminate some of the droning you get from resonance.

 

I've seen some HFC flow tests that rated at 85% of a test pipe. A resonator would obviously not be any worse than an HFC. Most of the estimates that I've seen suggest that a TBE is good for low 20's in hp. Is 2hp worth keeping the authorities off your back and eliminating some droning? Seems like a no-brainer to me.

I just ordered me the Okada plasma coils and a set of iridium plugs...supposedly good for 15hp on the high end and doesn't add any noise. When it comes to the stock exhaust the import thing is to get rid of the cat with *something*, beyond that there are many ways to get power without unpleasant side effects.

 

er...why would you lose power in a resonator, when it's just a straight pipe? perhaps you're mixing up resonator to a cat, since you're comparing it to a test pipe?

 

No...no mix up. A resonator is not just a straight pipe, or it wouldn't do anything more than a straight pipe would. It's an expanded section of pipe that has material to absorb the pressure waves that we don't want to hear. I just wonder how much hp this costs. And yes, I'm sure it's worth it no to hear the drone in a daily driver.

 

.5-1hp max hp lost... if any, probably would lose more via restrictive muffler.

 

technically it's a straight pipe. the holes are perforated, and the surrounding area utilizes frequencies to neutralize sound. plus pressure pushes the air out, not around (backpressure to be specific). it has nothing to do with air flow. a muffler could disturb flow, but not a resonator.

here's something that will help you: http://auto.howstuffworks.com/muffler4.htm

 

I think you're suggesting a resonator would cause the loss of the scavenging effect of the exhaust system and thus reduce power?

I could be mistaken, and someone correct me if I am, but I do not think that scavenging exists in a turbo system because the exhaust is "pressurized" as it leaves the engine when it pushes against the turbo's hotside turbine to spin it up anyway. Because of this, I think any scavenging effects are completely lost anyway.

Therefore, I think all you really want after the turbo hotside is as little restriction as possible. A straight 4" pipe right out the back (or side) is probably the best for getting every single last HP out of the car -- but it's NOT very livable for daily use nor legal.

I run a HFC, and Apexi catback with a resonator. It's very livable for daily use, doesn't attract any police, doesn't disturb the neighbors at night, sounds nice and aggressive without being annoying, and gives me plenty of power. I'm happy with it.

 

Yes, a resonator is just a straight pipe. It's a straight pipe that goes through the body of the resonator. When the exhaust enters the perforated tube, it doesn't expand into the resonator, it goes straight through the tube with zero restriction. You will lose zero horsepower and the exhaust will be quieter. It's like comparing a straight pipe to a straight pipe.

It's the same thing with any of the mufflers out there. Most of the exhaust systems available use straight through, perforated tube mufflers. This allows for maximum, unrestricted flow while allowing for a quiet tone. Resonators are just smaller versions to fit in where a full muffler wouldn't fit, so there's an additional muffler in the system to further quiet the tone.

 

A rather informative thread. I've found that an HFC & dual mufflers on my system are a nice compromise in sound level on the X's. The 8/9's are single-exit so I can see where an additional resonator might be desirable.