I read about a Variable Flap Muffler in another thread, I never heard of such a thing. What is it's purpose? Performance? Pollution control device? How is it controlled, electric servo? Vacuum? Does the flap ever stick? Sounds like a potential expensive fix.

Anybody care to educate me.

Tnx.

 

Ferrari and Mercedes have used the technology for years. It gives the muffler the ability to be an almost straight through design under WOT and when the "flap" closes the muffler becomes more civilized/OEM like.

 

XcarGo- are you talking about this?

Variable Capacity Muffler
A pressure valve automatically opens the exhaust flow wide at higher rpm to boost high-end power output and gives the G35 the growl of a hot rod. When rpm is reduced, as during idle, the valve adjusts to hush the muffler to nothing more than a soothing hum.

That is from the G35 description on Infiniti's site.
Wayne

 

GEE,
Thanks for that info. It sounds kind of like a Waste Gate type of a set up. A simple spring controls it all. Has anybody experimented with modifications to the system?

 

Yeah, I replaced mine with the HKS muffler and noticed a kick in the pants difference.

 

it actually does have a performance function. if exhuast is restricted at low end, you actually get more torque. but as the rpms go up, you need more. that's where variable intake/exhaust makes your money.
xcargo - what kind of mod were you talking about? adjusting it somehow?

 

There's no way to get to the valve short of cutting into your muffler.

Personally I think it's just there to make the exhaust quieter during low RPMs. I understand that there's a theoretical performance improvement by restricting air flow a little down low but I'd love to put a different, open muffler on and see what difference it makes both in terms of sound and HP.

 

The new VW R32 has this on there.

 

FYI, restricting flow doesn't improve lowend torque. Good exhaust velocity improves is what improves power. The variable capacity muffler improves lowend power by keeping the exhaust velocity ideal in relation to engine rpm. This muffler design has been used on the Skyline GT-R, 2001+ Maxima, Sentra Spec V, Altima, and now the G35 sedan. Like others have said, BMW and Benz have been using similiar setups for years.

 

No matter how you slice it, it is a compromise. Is it more effective then a conventional muffler that is quite from idle to redline? Yes. Is it as effective as a louder muffler that doesn't have the flap? No.

I got a chance to hear and do a ride and drive in a sedan that has the HKS muffler and a UT Y-pipe. While I didn't get to hear it rip up to redline, I was very impressed with the idle quality from the outside. On the inside, it was never intrusive offering just the right blend of sound.

 

daveb - that's what i meant -
tomato - potahto. i used a bad choice of words.

the concept works. it's been proven. i decided to go with the blitz rear section because i intended to go with a s/c. i felt that with the added pressure, that the stock rear section would keep up with the demand.
but with an n/a setup, it's a hard design to improve on.

 

The new ’05 Saleen S281 also uses a variable muffler system. The only reason it is on their car is to comply with federally mandated exhaust sound level restrictions imposed on vehicle manufacturers.

 

Yeah, but in the R32 it's an electronically controlled, vacuum-actuated valve. I've seen some good dynos on vwvortex where people have overridden the valve to get gains across the rev range, meaning both that there IS some advantage to keeping the valve open, and also that when the valve IS open via conventional means (vs overriding it) it's not opening all the way. ie - valve open electronically = xHP @ 5600RPM; valve overridden = x+8HP @ 5600RPM... if you catch my drift.

Personally I'd like to just replace my muffle with a nice looking one that sounds a little deeper and has some nice looking tips, I'm not a fan of the stock "faux" tips.