How much interest do people really have in a quiet high-flow exhaust?

[BAC5.2]

wow.. that's more than good enough for me!

 

Any supporting mods like intercooler/bov/etc?

 

got a dyno plot/sound clip?

 

It sounds almost stock, just a little louder from outside the car. About the same from inside.

 

No other mods, though I genuinely think the heat protection I did helped a little.

 

The exhaust we have been working on should be here from Australia on Monday! Going to do a test-fit on tuesday!

[TRSCobra]

^^^ I'll be expecting pics on Monday and pics on your car on Tuesday!

[BigTDogg MA]

I made 263whp and 337ft-lbs. It's reasonably quick.

 

At Stage 2? Damn! What are the estimated drivetrain losses on a MT AWD LGT/OBXT?

 

I'd be interested (with internet dollars) in an exhaust which started out 3", has a resonator, splits to dual 2.125" then goes to straight through mufflers. Dual 2.125" would be the closest size to a single 3" you could get, though I suspect your muffler choices would be limited, so 2.25" or even 2.5" would have to do.

[BAC5.2]

Pics will have to wait for Wednesday.

[BAC5.2]

At Stage 2? Damn! What are the estimated drivetrain losses on a MT AWD LGT/OBXT?

 

I'd be interested (with internet dollars) in an exhaust which started out 3", has a resonator, splits to dual 2.125" then goes to straight through mufflers. Dual 2.125" would be the closest size to a single 3" you could get, though I suspect your muffler choices would be limited, so 2.25" or even 2.5" would have to do.

 

No idea on losses. Probably in the 18-20% range.

 

Two 2.125" pipes won't flow the same as a single 3".

 

The prototype exhaust we are putting together is 3" with 2.5" y-pipes. The midpipe we are test fitting is plain at the moment. Production will have some neat features, including one that you can't get with any other exhaust right now.

 

Mufflers are still being finalized, so those aren't ready yet.

[BigTDogg MA]

Two 2.125" pipes won't flow the same as a single 3".

 

The areas are equivalent

[frank_ster]

^ the area's may be the same but the flow is not simply based on area.

 

its because the circumference causes drag. but it really depends upon the fluid and surface finish of the pipe.

 

but it does sound reasonable. and if the pipes are short it should be fine. it will stabilize the pulsations.

[BAC5.2]

The areas are equivalent

 

They are. But that doesn't mean they will flow the same.

 

The internal pipe surface area is almost a third higher for the pair of smaller diameter pipes.

[BigTDogg MA]

They are. But that doesn't mean they will flow the same.

 

The internal pipe surface area is almost a third higher for the pair of smaller diameter pipes.

 

It's your best approximation without getting into boundary layer equations, IMHO, unless there's some other simple formula or rule of thumb I'm unaware of.

 

The surface area isn't known without having a length. You only have planar area and circumference. The surface area increases with the diameter of the pipe anyway, so I'm not sure what you're trying to say about the two smaller pipes.

 

Exhaust flow is anything but laminar, but the amount of surface area does play a role in the boundary conditions and maintaing flow. So perhaps 2.25" would be better suited to maintain exhaust velocity. I just know 2.5" is too big.

[BAC5.2]

It's your best approximation without getting into boundary layer equations, IMHO, unless there's some other simple formula or rule of thumb I'm unaware of.

 

The surface area isn't known without having a length. You only have planar area and circumference. The surface area increases with the diameter of the pipe anyway, so I'm not sure what you're trying to say about the two smaller pipes.

 

Exhaust flow is anything but laminar, but the amount of surface area does play a role in the boundary conditions and maintaing flow. So perhaps 2.25" would be better suited to maintain exhaust velocity. I just know 2.5" is too big.

 

There is a simple rule of thumb. As surface area increases, flow potential decreases.

 

If the length of the pipe is the same, then surface area is proportional to the circumference of the pipe. If all the pipes are 12" long, the length drops out. Try it with different pipe lengths, and you'll see. If the pipes are 24" long, or 56" long, or 1,000,000" long, the ratio of surface areas are all the same.

 

2.5" y-pipes are perfectly suitable for almost all reasonable flow purposes. 3" y-pipes have even shown benefits on the 08+ WRX's when pushed. If you want a 2.25" exhaust, then you might as well stay stock.

[GEE-OTTO]

Avo's is not resonated...so it will be louder than stock with stock mufflers attached.

 

Hey SBT this is odd but AVO does in fact make a resonated Y pipe they make a 2.5i and LGT specific pipe. I think the 2.5i pipe would work well for 95% of LGT below owners as 2.5" wont adversely affect exhaust flow.

 

http://www.avoturboworld.com/avoshop/images/thumbs/300_25_center.jpg

 

Here is the LGT specific one :

 

http://www.avoturboworld.com/avoshop/images/thumbs/300_leg_cpipe01.jpg

 

This one is 3" could be a good option for us all.

 

Side note user "itsme" exhaust on his wagon is my goal/perfect exhaust note

[apexjapan]

As Gee-otto noted, all of our mid/y-pipe systems are resonated. The bottom pic of the 3" is old, I need to unpack and re-shoot pics of it. The top picture of the 2.5" system is a much more accurate representation of the current 3", as the 3" and 2.5" are the same basic design, just different diameter piping and a slightly bigger resonator on the 3".

 

Regards,

 

Paul Hansen

http://www.avoturboworld.com

http://www.facebook.com/avoturboworld

[Gary Bechtold]

Got an updated AVO 3" picture? I'm interested in it for my A/T '05 GT Wagon.

[apexjapan]

I'll unwrap a set and take pics of it today!

 

Regards,

 

Paul Hansen

http://www.avoturboworld.com

http://www.facebook.com/avoturboworld

[apexjapan]

Update images!

 

http://www.avoturboworld.com/images/stories/2011/leg_midpipe/05leg_midpipe_001.jpg

 

http://www.avoturboworld.com/images/stories/2011/leg_midpipe/05leg_midpipe_002.jpg

 

http://www.avoturboworld.com/images/stories/2011/leg_midpipe/05leg_midpipe_003.jpg

 

http://www.avoturboworld.com/images/stories/2011/leg_midpipe/05leg_midpipe_004.jpg

 

Regards,

 

Paul Hansen

http://www.avoturboworld.com

http://www.facebook.com/avoturboworld

[SBT]

Paul,

 

That's good to hear that they are now resonated - and those are some shiny bits. 20 months ago when I was looking for a Mid-Y, the AVO mid-pipe wasn't available with a resonator (and I asked), so had to go another route.

[Clyde Smiff]

Paul, will the AVO exhaust system (catback/mufflers or just mufflers) fit an 05 LLB 3.0R?

[socalsleeper]

Do I expect this to happen, no. But I would like to see a two stage muffler, something with an actuator that can be controlled from the cabin. Some OEMs already do this but they weigh a ton and are not too good looking.

I can hope right.

[thefultonhow]

Do I expect this to happen, no. But I would like to see a two stage muffler, something with an actuator that can be controlled from the cabin. Some OEMs already do this but they weigh a ton and are not too good looking.

I can hope right.

 

I have that. Perrin mid/Y with an electronic cutout at the Y, going into stock muffers. Quiet when I want it, powerful (and LOUD) when I don't care.

[socalsleeper]

That is not at all what I mean. I am not trying to bypass the mufflers, I would like an exhaust system that has muffler that will have more than one flow path. Straight for power, and muliti pass to be quiet.

Which will not happen. But I can dream right.

[TRSCobra]

IIRC, 06+ corvette Z06 mufflers have this setup, but I'm not sure if they'll fit on our cars.

[socalsleeper]

I know Rs4 Audis have this as well as some Porsches but they are an OEM part almost nobody in the aftermarket makes a product like that.

[TRSCobra]

The trick is finding a set of OEM take-offs on ebay that'll fit. Some BMWs have them too.

[frank_ster]

Do I expect this to happen, no. But I would like to see a two stage muffler, something with an actuator that can be controlled from the cabin. Some OEMs already do this but they weigh a ton and are not too good looking.

I can hope right.

 

they have them .. 12 volt actuator on a muffler for quiet or loud.

 

its like 270$ muffler.. i'm not sure who sells them.

[BlackGT]

Here's a quick lesson in automotive exhaust acoustics:

 

Unfourtunately, sound quality is in the ear of the beholder. What I find pleasant (in tonal quality and volume) is not always what others find pleasant. I've had 3 different aftermarket exhausts on my 05GT and they all sounded awful to me. Yes, maybe they sounded good when wide open, but not when just driving around. So, in order to get a good-flowing and good-sounding exhaust system, we need to apply some engineering, not just poke and hope.

 

The noise coming from the combustion process is broadband - it is composed of all frequencies in the audible range.

 

Absorber silencers (mufflers), the kind with glass or stainless packing, are only really good at absorbing above 500hz, the drone we get in our cars is at 100-200hz. While adding an absorber muffler will bring down overall noise levels, it will not do as much in the lower frequencies as a reflective silencer. I like to incorporate both absorbers and reflectors in the exhaust systems I build. The absorber removes the hi-frequency rasp, and the (properly designed) reflector removes the drone.

 

A large amount of silencer volume (capacity) is important, target 10X engine displacement, which means 25L for our 2.5L engines. (most aftermarket mufflers are smaller than our stockers, which drives UP noise levels) All absorber and reflecter silencers count towards this volume. Some people even count the pipe volume, but it proven that a larger tube diameter (say 3") has less transmission loss (read: louder) than a smaller (say 2") tube, so I don't count pipe volume. Going off memory, a 3" tube is 7% louder than a 2" right off the bat.

 

I build exhaust systems which incorporate 1/4 wavelength cancellation (very small freq band attenuation), helmholtz resonators (slightly wider frequency attenuation), absorbtion, and reflection.

 

Most consumers would prefer to buy systems made overseas that look pretty, but sound poor.

 

Tailpipe length is important too (remember to count what is inside the muffler), as it can amplify troublesome frequencies if designed incorrectly. Or, it can be tuned to amplify nice sounding frequencies and improve sound quality.

 

A lot of good info can be found in this book:

[ame=http://www.amazon.com/Engineering-Noise-Control-Theory-Practice/dp/0415487072/ref=sr_1_1?ie=UTF8&qid=1319111260&sr=8-1]Amazon.com: Engineering Noise Control: Theory and Practice (9780415487078): David Bies, Colin Hansen: Books[/ame]

 

The attached graphs are actual measurements from my 05GT. They are from a neutral sweep, no engine load, measured at drivers inner ear and tailpipe exit. These are old graphs and show what I believe is UNacceptable in an aftermarket exhaust, see how the interior overall noise level gets louder and softer as the RPM's increase? Thats bad.

 

Jeremy

baseline3.pdf

baseline2.pdf