exhaust too loud?

[Quinton Exler]

Currently loving the deep tone keeping my top cat gives. Keeps the response tone flat in my opinion. However if i upgraded from the downpipe and back to 2.5" how much louder would it be? Keeping top cat.
Also been studying bandpass exhaust systems. Don't wanna be too loud though.

 

[ThatTmoGuy]

I've never heard of bandpass exhaust, do you have any sources?

The only bandpass system I've ever heard of has to do with a sub enclosure.

 

[Eric Smit]

Top cat? The one in the downpipe? You want to upgrade your downpipe? There isn't a catted upgrade?

I don't know what you mean by top cat.

 

[Quinton Exler]

Kind of just playing with the made up "bandpass" exhaust myself. I have came to realize a lot by comparing subwoofer calculations and ideas to my exhaust system. Proper sizing is a must however to make it work. For example... A traditional ported subwoofer enclosure is a similar concept to a straight pipe exhaust, upgrading manifolds can increase hp and flow just as 45s and flares do in a good enclosure. However any avid box designer who has it all to a science knows that a 4th order bandpass (half sealed, half ported enclosure) has a smaller sealed side on the main pressure side and the ported side being 2-3x larger rule of thumb. Oddly with a 4th order you Wolff expect it to move less air from the ported chamber than a traditional ported does because its back movement is contained in the sealed side... A 4th order is not only louder but it moves more air as well. Because of back pressure and front pressure properly working to move the air through the ported side.

 

[ThatTmoGuy]

I'm pretty sure you're over thinking the exhaust system. K.I.S.S. straight pipe it and if it's too loud add a resonator.

 

[Quinton Exler]

I just really think it could work well being assisted with pressure. I just like being different. Just don't want it to be obnoxiously loud. And the resonator would ruin the bandpass idea sadly. Trying to do something new!

 

[firstorbit84]

You could do straight pipe with a branch style resonator of a specific length to tune out any drones or unwanted frequencies.

These are from my old Audi A6 4.2:

 

[Quinton Exler]

Very nice setup, that is very custom and unique and I would feel proud to drive such a uniquely modded car! I know everyone is thinking I am probably slightly crazy with this "bandpass exhaust" idea that implements using pressure to force exhaust out rather than just letting exhaust flow completely free with a straight pipe. If you really think about it thought it seems like it could work really well. Implementing the pressure the engine builds to create somewhat of a build spot and the two sides of pressure could force the exhaust rather than letting it just fall out in a traditional straight pipe. If the calculations I came up with using HP, Torque, And trying to keep in mind future modifications is correct than I think a 2.5" pipe would be minimal and a 3" would work optimally. However I do not want to have a full custom bent 3" pipe made and welded on then it comes out being ridiculously loud... Or would the top cat be enough to deaden the sound that travels after it?

 

[ThatTmoGuy]

Quinton you do not want to "pressurize" your exhaust in a turbo application. I know what you're thinking velocity vs flow and what not. If this is just about the actual sound then give it a shot.

 

[Eric Smit]

if you don't want it loud, then you need a resonator/muffler.

ideally, you want the exhaust flowing as fast as possible out through the turbo to spin it up.

If you only care about sound, ignore first two points.

And what the derp is a top cat?


-Eric Smit

 

[Quinton Exler]

Quinton you do not want to "pressurize" your exhaust in a turbo application. I know what you're thinking velocity vs flow and what not. If this is just about the actual sound then give it a shot.

Thank you, I would like the sound a little better that way I believe... I was not only considering pressure/velocity build VS. Exhaust movement with no pressure. I am attempting to remove more exhaust than a traditional straight pipe could by implementing back and front pressure. As you said, you want to move exhaust out as fast as possible in a turbo application and hold no exhaust back. (I really appreciate your input! Thank you!) However what is implementing pressures could remove the exhaust even faster than a straight pipe alone could?

 

[Quinton Exler]

if you don't want it loud, then you need a resonator/muffler.

ideally, you want the exhaust flowing as fast as possible out through the turbo to spin it up.

If you only care about sound, ignore first two points.

And what the derp is a top cat?


-Eric Smit

Well I am sure I used the incorrect terminology, Its the first catalytic convertor in the series.

 

[Eric Smit]

which is located in the downpipe. if you want to keep the cat there, which is not ideal for performance, you don't have an upgrade option. The only downpipe available is catless.

The cat does plenty for muffling and pressure, both of which are bad for performance.

If all you care about is sound and lots of pressure, leave it.


-Eric Smit

 

[ThatTmoGuy]

You're talking about the downpipe here for mentioned as the DP.

The only thing i could think of to actually increase pressure and flow would be using a nozzle similar to what is used in rocket motors

Richard Nakka's Experimental Rocketry Site

The unique shape and design of the nozzles will increase the velocity of the expended gasses, this could work very well in an NA motor (no forced induction) but due to the fact that it would increase back pressure as well it would slow down the spooling of the turbo. Which in turn would be a loss in performance, If you want to take the time i would suggest reading that link

 

[Quinton Exler]

which is located in the downpipe. if you want to keep the cat there, which is not ideal for performance, you don't have an upgrade option. The only downpipe available is catless.

The cat does plenty for muffling and pressure, both of which are bad for performance.

If all you care about is sound and lots of pressure, leave it.


-Eric Smit

Thank you Eric! I will have to try this for myself I suppose and see the results. Do you believe the 1st cat would deaden sound enough to where a 3" straight pipe wouldn't be overkill loud?

 

[Quinton Exler]

Thank you TMO guy! However I am attempting to create a concept much different from that one! That would be a horn like effect starting small and ending obnoxiously large which would be only for a sound application, It would increase the pure waves of pressure more into a sound wave like effect. I am Attempting to use both back and front waves to spool the turbo and release exhaust. However that is an excellent read! Thank you!

 

[ThatTmoGuy]

At any rate get some before and after Dyno #'s so you can have some proven results on what the mods do. The best bet would be to make the exhaust system and bring the stock exhaust with you, run the dyno with your custom piece then replace the stock and see what/if any improvements have been made.

 

[Quinton Exler]

I shall! do that for everyone TMOguy! and the results may be as soon as tomorrow if a dyno is readily available! Question still remains, would 3" be overkill loud if the downpipe is still in place? Of course somebody may know for sure... I am just wanting opinions. Currently I don't think it as loud at all with stock pipe and 1st cat only remaining.

 

[Eric Smit]

Thank you Eric! I will have to try this for myself I suppose and see the results. Do you believe the 1st cat would deaden sound enough to where a 3" straight pipe wouldn't be overkill loud?

most definitely. the downpipe/cat combo is very muffling.


-Eric Smit

 

[Quinton Exler]

Regardless of anything, a 3" pipe coming from the rear of my car would look HAWT! However I am hoping for a better HP output.