Dimka.m

Hey!

Was reading Autoweek and had a few questions about the butterfly valve in the exhaust (closed for more low end, open for more topend). g.smurf in clubrsx.com said that possible that Maxima SE has same type of deal?

Is that true? Has anyone shown actual gains from it?

Thread at www.clubrsx.com

Thread at bimmerfest.com

Norm02SE

Yes the 02's have them.Gains would be hard to say due to the car comes with it stock.Would have to take it out to tell the difference.Doubt it does anything except create more and less backpressure through the RPM.

Tanman

The 2K-2K1 Maximas have this feature. Not sure about the 2K2. I think it's main purpose is to cut down on noise. If you think about it, when both flaps are open, you have freer flowing exhaust, which helps. But if you actually take a look at a diagram of the Maxima exhaust, you'll see that exhaust has to run through a maze before it makes it out of the second pipe of the muffler, so it really isn't that much freer flowing.

Dimka.m

Do you know if anyone actually have removed them to check? Probably not though... :)

See that's the problem: it creates more or less backpressure throughout the RPMs... but WHY? Why would the engineers put something that's fairly sophisticated in there? :confused:

That's my goal in life right now to figure out why. :)

If you read the posts at clubrsxt then you know that ferrari has that same setup, I was thinking of sending an email over there but I doubt there will be a response. :)

y2kse

iTrader: (1)

Well you're partially correct and partially incorrect, Tanmann9. You are correct when you say that the main purpose of the valve is to cut down on noise. But you are not correct in saying that the muffler is very restrictive when both valves are open. If it was, do you think Nissan would use the same design on a Skyline?

When I switched from a Magnaflow back to my OEM rear section, I didn't notice any decrease in performance. Of course, I've only got my butt dyno to rely on. But that's good enough for me.

Tanman

I seem to be 50/50 on everything I post

If you've seen a cross-section of the muffler, you'd see what I was talking about. There's like 3 chambers, and if there's enough exhaust in the primary chamber, the pressure will open a flap that lets the exhaust into a second chamber, then down a tube into a third chamber where it flow out of the second muffler pipe. I can't find the image, but I'm searching for it.

y2kse

iTrader: (1)

Right. I have a diagram of the muffler here. Granted it's not as free flowing as a straight-through muffler . . . no chambered muffler is . . . but the chambered design allows the muffler to be relatively quiet while maintaining sufficient flow to keep backpressure to a minimum. And that's what counts.

Tanman

Can you post the diagram?

y2kse

iTrader: (1)

Nope. But I can e-mail it to you and you can post it if you have a web site. Send me an e-mail at bld522@yahoo.com and I'll return it to you as an attachment.

97GLE

Demonstration Video - QuickTime

There ya go

Dimka.m

Interesting, they said that variable-flow muffler is designed to improve power at high RPMs and reduce noise at low rpms. Nothing about power at low RPMs

y2kse

iTrader: (1)

I'd say that explains it, all right. Thanks 97GLE.

y2kse

iTrader: (1)

Well let's think about it for a minute. The valve opens when exhaust pressure builds up in the muffler, thereby allowing exhaust gases to escape from both outlets. If I understand the operation of the muffler correctly, sufficient pressure can build up at both low rpm and high rpm to open the valve. The valve is normally closed only at idle or when the vehicle is coasting.

Does that make sense?

Tanman

Thanks, that's where I saw the design. The stock muffler seems a bit over-engineered, but has a decent sound around 2100 RPM.

Dimka.m

Hmm... I understand what you're saying. But that would mean that this valve is open under any hint of acceleration. This is probably not what I'm looking for, or I just don't understand the concept. Here's an excerpt "Butterfly valve in tailpipe (below) controls backpressure, closed for low-rpm torque, open for peak power." It's taken from May6th edition of Autoweek regarding Ferrari 575M.

It is also possible that I am totally lost and confused. See, the idea poped into my mind that maybe such a setup could improve lowend torque on my RSX-S. That is always a welcome thing.

y2kse

iTrader: (1)

Yeah, dammit. What do those Skyline engineers know anyway?

y2kse

iTrader: (1)

Keep in mind that the concept of "good" backpressure is a complete myth. Do a search under "backpressure" in the 5th Gen forum and you'll see what I mean.

I have also heard a couple of different explanations as to the operation of the valve. But the bottom line is, it seems to work the way it's been suggested. And again, I didn't seem to lose any performance when I reinstalled my OEM rear section. So when it comes to a tradeoff between noise and performance, I'm still giving a "thumbs-up" to the OEM muffler.

2K1HoMax

all that thing does is allow the muffler to flow more freely at higher rpm, dont know exactly what point it open up but i know its aroun 2400rpms-2800rpm if u drive like a normal sane person (which i dont) and u have the stock muffler, take a look into the tailpipes(NOTE: WHILE THE CAR IS OFF) ull see that one side is black from the exhaust, if both are black that means congrats ur butterfly valve works just fine, both mine are black.....thats how u can tell if some1 has hammered the car alot if ur gonna buy a 5th gen used, if on side is very clean, chances are that car hasnt see too many high rpms.

y2kse

iTrader: (1)

Good advice, 2K1HoMax!