does my 2k max have a flap in it that opens up after a certain rpm range or air flow coming out. i'm asking because i put in a y-pipe, gutted cat, and just ran 2.5" pipe and the car sounds good, but has a flap type sound to it at start up and pops a little when coming down in rpms, just curious

 

yes...there is a flap. It's to keep backpressure at low rpms and it opens up at high rpms (I think it's like 5500 or something)

 

is there a way to get rid of it and if not is borla a good muffler to get for me 2k se

 

ok now im really confused...are we talking about the flap that opens up in the the left pipe coming out of the muffler? cuz i read a post a LOOONG time ago, and someone said that it opened ~2500 rpms...

 

Actually, its 3800.

 

So, are there any positive or negatives of having it on/off? I am getting ready to do some exhaust work in a couple weeks and this is the first time I have seen a question posted in the forum about said flap.

 

This isn't the same thing as VIAS that is activated around 5k RPM?

 

dude it opens when u floor it.. or you are on highway

 

will someone please just answer my question, i now know that there's a flap and it opens, don't care where or when it opens just wanted to know if i can take it out or not

 

Nissan calls it a variable capacity muffler. It basically becomes less restrictive at high rpms and more restrictive at low rpms.

It's not exactly a myth that you need some backpressure to have a properly tuned exhaust, but it is misleading. In reality, you need to maintain a balance between exhaust gas velocity and backpressure. If there isn't enough backpressure (like when the piping is too big), exhaust gas velocity will drop, which hurts performance. If you decrease the pipe diameter too much in an effort to increase exhaust gas velocity, you will have too much backpressure (once again, this will cause performance to suffer).

If you know how a four cycle engine works, then you know that after the fuel and air combust, the piston comes down and then moves back up the cylinder as the exhaust valves at the top of the cylinder open. The piston effectively "pushes" the burned fuel and air (the exhaust gas) out of the cylinder, dumping it into the stock exhaust manifolds or aftermarket headers, then it goes down through the cats, the pipes, the mufflers, or whatever you have in your exhaust setup. As long as you keep the exhaust gas moving quickly through the entire exhaust system, it creates a "vacuum effect" that helps keep slow exhaust gases from building up at any point in the system. Since your car produces a lower volume of exhaust gas at low rpms, the exhaust needes to be a little more restrictive in order to keep the exhaust gas moving at a good speed (or else there would be no "vacuum effect"). If your exhaust were too open or if your piping were too big, you would lose a lot of low-end torque.

When you reach higher rpms, your car is producing a higher volume of exhaust gas, so the muffler opens up a less restrictive route for the exhaust gas. If the muffler did not open up to accomodate the increase in exhaust gas, then your exhaust gas velocity would still stay nice and high, but instead of creating a low-pressure "vacuum effect," you would end up with exhaust gas piling up in the pipes as it tried to get out. By opening up the less restrictive route, you maintain the balance between exhaust gas velocity and exhaust pressure.

In short, keeping the flap open all the time would probably hurt your low end performance slightly, but it wouldn't have any effect on your performance at high-rpms, since the flap is usually open then anyway. Lots of people who install aftermarket headers or y-pipes notice a popping sound even if they don't have variable capacity mufflers. Your exhaust was engineered for a balance between performance and quietness. You have shifted its design a little more toward performance and a little less toward sound comfort, so now you're hearing some of those noises that the Nissan engineers tried to hide from you.

 

Sorry for my long post. In answer to your question, I believe that the flap is a fairly simple device. There are no wires or sensors leading directly to the muffler, so it's not a computer controlled thing. It's probably just spring loaded to open when the exhaust reaches a certain pressure. You could probably rig something up to hold it open or remove it entirely without causing an SES light or anything. I'm sorry I don't have a more detailed answer, but not many people want to hold the flap open permanently, since it would result in a loss of low end power.

 

but how are u going to remove it?

 

It is NOT removable. You will have to cut the muffler open, but then it becomes useless. It you think its possible, I challenge you to prove me wrong. Also, post a writeup to contribute to the community.

 

I am thinking of a new exhaust also. The stock one is too quiet for me. So, I guess taking off the stock muffler won't mess with anything. Good to know.

 

You almost have it right, there is no such thing as backpressure. It was a word invented to describe the effect of poor gas flow. Also, the ideal exhaust is one with no "backpressure" (because of the scavenging effects).

 

As said above, i dont think there is a way to get rid of it. But to answer your question about a borla muffler i would say go for it. I just put mine on and i love it!
Hope that helps you answer your question.

 

thanks a lot for the answer, what borla did you get?

 

I think I'm going to have to add this one to the FAQs, if not already:

http://forums.maxima.org/showthread....t=muffler+flap

 

I will comment on Borla as I have owned a Borla muffler before. Borla makes some of the highest quality mufflers around, BUT I believe all of them are a straight through design (as are just about all aftermarket mufflers). They have nice deep growls to them and the one I had did not drone AT ALL. They also build some very high quality catbacks and I have yet to hear of anybody having a fitment problem with a borla system. The muffler carries a lifetime warranty as long as you do not weld anything to it.

IF you don't mind a louder exhaust a borla would be my choice 9 out of 10 times.

 

Magnaflow > all

 

By the way, this isn't just some dumb trick that Nissan came up with. Have you ever heard of a little car called the C6 Corvette Z06? I just found an article about its new features, including its exhaust...

"Due to rising costs, those mufflers are steel instead of titanium, as they were on the previous Z06, but they are sophisticated in a different way. At low revs, all the exhaust goes through a single well-muffled tailpipe in each muffler. When you stomp on the throttle and exceed 3500 rpm, however, vacuum-powered bypasses open up a second, virtually straight-through tailpipe in each muffler. That sound will be worth the wait."

Car and Driver calls the Corvette Z06's variable flow muffler "sophisticated." I guess nobody told them that our Maximas already have a similar setup.

 

Yeah, but opening up to a straight through type muffler on the C6 Z06 is way different then the reverse aborbtion type muffler on the Max whose main objective is sound suppression below 2000rpm.

Yes, it's a stupid gimick and not a performance oriented design like the new Z06.

 

whatever you do, don't try to prove spiromax wrong- he is exactly right! yes there is a flap, and you don't want to be like this one honda owner i know who tried to tell my buddy that his max does not have a flap! this idiot tried to stick a long screwdriver in my buddy's exhaust so he can hear the flap and ended up dropping the screwdriver in the muffler! my buddy had to have his muffler changed after that, and now the screwdriver resides in honda boy's rearend! fyi (honda = how n da f*%# did you end up with that car?) that's usually what i let the honda owners know!

 

I'm no expert. I'm just a guy who reads too much. I've asked some people with aftermarket setups here on the Org, and more than a few have told me that the stock muffler combined with an aftermarket b-pipe is a decent setup if you want to have a slightly more aggressive sound without making the exhaust too loud. Of course there are other mufflers that work. The stock variable capacity muffler is not the absolute best one in the entire world, but it's not excessively restrictive when you're at high-rpms, so it's pretty good for a stock muffler.

If the flap annoys you for some reason, get a muffler without one. I'm staying with the stock muffler after I switch to an aftermarket y-pipe and b-pipe because saving a little money never hurt anybody. If the sound of the flap opening starts to bother me the same way that it's bothering xlcrew, then I may end up switching too.

 

I figure I'll give my $.02...
About a month after I got my Maxima, I went and got custom piping done.
2.5" from the cat back to an OBX Racing Muffler. It's just basically a hollow canister. My exhaust was loud as hell.
After getting pulled over about 3 times for the noise, I decided about a week ago to put the stock muffler back on (Actually I bought Jesse's with nice Magnaflow tips on it). So now I'm running 2.5" from the cat to the stock muffler.
My performance now is the best it's ever been.
My car pulls much harder than it did before and my shifts seem smoother.
The sound is much better... Closer to like a 350z sound.
The butt dyno feels like there was a definite increase in torque.
I also believe in the concept of back pressure and I believe that a car has to have some back pressure to function correctly.

In short, my reccomendation from now on when someone mentions they're looking into getting an exhaust.... 2.5" from the cat to the stock muffler... I give it

 

The VIAS, I believe, is on the intake, not the exhaust.

 

butt dyno proves nothing

 

I didn't say it "proved" anything. In my opinion I really felt a difference. The other muffler was just too wide open.

 

It's all in your head, people have removed the axle back section and gained 3whp, so unless the OBX was more restrictive then OEM, I doubt it, the ole butt dyno failed again.

 

Horsepower is a tricky thing. If they gained 3 peak horsepower by removing the axle back section, that power might have come later. The butt dyno is a TERRIBLE indicator of how much horsepower your car can put down to the ground, but it is sensitive to changes in the distribution of torque and power along the powerband. I have no doubt that removing the axle back section produces a gain in horsepower, but it probably changes the shape of the dyno graph too. That's what the butt feels, and that's why the butt dyno is unreliable.

 

In my unprofessional opinion, I may have lost 3 peak hp and like you said the butt dyno is not reliable for hp. However, I know how my car and i know how it felt before and how it feels now.... It pulls better than before. More torque maybe due to the redistribtion of power?