Tips on choosing an exhaust system...

Dropped by a local bookstore and spent an hour at the automobile section. Picked up some good tips on how to choose a performance muffler.



What I am about to write here is based on what I read. Well, the author first claims that most "glass/fiber" filled mufflers out there are driven by false marketing. Most of them actually reduce performance when compared to a stock muffler. But there maybe a couple which actually do reduce backpressure. A couple of tips on choosing a good muffler are:

1) when you pick up the muffler, hold it towards a light source. Look through from the tailpipes. If you notice the pipes reducing in diameter from the inlet to the outlet, then this muffler INCREASES backpressure.

2) If the pipes are perforated, notice how are the holes punched on the pipes. If they are punched inwards (away from the muffler housing), meaning creating a sharp profile around holes, then this design actually
induces turbulences around the holes, thereby INCREASES backpressure. If the holes are punched outwards (towards the muffler housing), this design should work as it should be (ie to decrease backpressure).
Note that a careless hole-spacing design can also create Eddy currents when the exhaust flow runs through the pipes. This can INCREASE backpressure too.

Also, a perforated muffler is known as an absorber, cos it "absorbs" the exhaust note. Another interesting fact about the perforation is that they create the special "deep, throaty" note when hot air runs over them.

Imagine a flute. When you blow through the mouth piece and at times covering the appropriate holes, you can create a specific note. Same principle.

Perhaps the most ideal design is to totally eliminate the perforation. No doubt about that. But that will increase the muffler note, which, well, can creat noise pollution.

So, SS, AA, UUC, Remus, Borla or Eisenmann...they are all straight pipes and most likely perforated. The design will then be how the holes are punched and spaced. Also, taking welding techniques and quality into mind.

Thanks! Very useful information. Keep it coming!

-SilverBmw

14 views and only 1 reply. Perhaps the rest of the 13 viewers think I am MAD!

Originally posted by SilverBmw
Thanks! Very useful information. Keep it coming!

-SilverBmw

we're just lazy bastards

besides I'm playing with my most entertaining xmas gift
antiperspirant in an airisol can!

I think the whole thing about "performance" mufflers is nonsense. I bought and tried several "performance" mufflers on my hypo 91 Talon. Each one gave different sound but power was a wash.

In other words, if the muffler gave some more high end pull, it was weaker at the low end. Conversely, If it was stronger at the low end, it was weaker at the high end.

Basically, the muffler adds very little to the power of a car... it changes the look and sound... but little else. My 91 Talon Turbo was very modifiable from the intake and exhaust side. I felt big power increases with Cold Air Intake, Intercooler pipe upgrade, less with Exhaust Downpipe (header to cat) & cat upgrades and the lease from the exhaust.

From my experience, I would look elsewhere for increased power.

- JP

How much power increase is to be expected with mufflers,CAI etc? just wondering.

Alex

From my reading, the expected power increase is from 0-3%. I'd only trust dyno readings for certain.

In any case, I think JP had it right: aftermarket exhaust systems change the sound and look much more than they impact performance.

The intake on a normally aspirated car is worth about 10hp. On forced induction cars can be higher, in the 15-20hp range.

The exhaust is anywhere from 0hp-5hp... but as I wrote, from my experience it's closer to the lower end. On an E46, I'd bet it was next to 0 and even if it was 5hp, I doubt you could feel it.

However, there is a benefit to an aftermarket exhaust, beyond sound&look.... I noticed massive differences after intake & exhaust work was done to my Talon on hot&Humid summer days. Turbo vehicles are susceptible to hot days and they turn into slugs breathing the humid air (Turbo wants cold air). The intake & exhaust mods translated into much better air movement (breathing) for the vehicle, which made it much less susceptible to air temperature&humidity.

My Talon would provide a noticeable amount of improved power on hot days after the mods than before. Normally aspirated cars are less susceptible to the heat, but they still feel it. So, while your aftermarket exhaust may not give you much power in general, it may help your car breath better during the summer, thereby minimizing power loss. If you live in the hot climates and notice this power loss, an aftermarket exhaust may help you out a bit.

- JP

So if we were to exclude performance from the mix and focus specifically on the quality and note of a give exhaust, what manufacturer / design is best? I mean, does one company produce a more natural sounding, better built exhaust than others. I have been looking for a while now and like the UUC "Twin Silencer" for the E46 330Ci that was just released but no one can rate it yet, at least I haven't found anyone that has it.

But others... there are so many choices here and though science plays a HUGE part in the note (flow, resistance, backpressure etc.), the manufacturer plays as much in the quality (metal choice, weld quality, etc.) but it is all so subjective. What to do?

15-20hp is a considerable amount of increase. I was expecting less. But what about the drivetrain, gearbox and brakes on a car with modded engine?

Alex

Originally posted by VinceTopasBlau3

1) when you pick up the muffler, hold it towards a light source. Look through from the tailpipes. If you notice the pipes reducing in diameter from the inlet to the outlet, then this muffler INCREASES backpressure.

Easier said than done, the only one that I have actually held was a Dinan exaust, both for the 323/328 and 325/330. Looked nice. Definatally straight tips (I could see light at the end) I would like to get a performance muffler for the sound and gain, but it is pretty expensive.

There are those who like the ECIS exhaust, as I recall. They like the exhaust note, in particular, I believe. There are innumerable threads on this topic at e46fanatics.

Glad that so many pple replied!

Well, first thing first, I am also glad that JP brought up "performance muffler" being nonsensical. Yes. But for those who might have misread this two words, they don't imply that the improving the entire exhaust as not producing any performance.

Muffler is just the last line of defense for performance modifications to the exhaust system. One has to look at the cat-convertor, resonator, headers etc...

We are playing around with the concept of reducing backpressure? Why? Because of the inhale/exhale process of the engine. View the pipings, cat-convertor, resonator and mufflers as obstacles that the exhaust fluid has to flow across. Each added obstacle will slow down the flow, thus producing backpressure. If you just replace the muffler, you probably won't feel much of a difference. I can bet with you with the data from the Dynometer on this. But if you remove one of the obstacles (e.g. resonator or cat), you WILL feel a slight boost. Most ideal system? remove the headers, resonator, cat and muffler. Have the exhaust directed from where the engine is located.

Hence I have been preaching to get Eisenmann. Quality, handcrafted and made in Germany, yet cheaper than most out there. Plus you get that tailpipes quite like Dinan's.

Originally posted by nate328Ci


Easier said than done, the only one that I have actually held was a Dinan exaust, both for the 323/328 and 325/330. Looked nice. Definatally straight tips (I could see light at the end) I would like to get a performance muffler for the sound and gain, but it is pretty expensive.

I just discussed about the UUC system with 31st330i. Ok, they did release a sound clip, where it grumbles quite like an Eisenmann. So, wah lah! We have found a system that sounds good. So, if in person the UUC system sounds as good as an Eisenmann, then why not go for the latter? Cos it's handcrafted, German made and of a good welding quality and still cheaper.

Btw, I don't work for Eisenmann.

Originally posted by LilEccentricJ
So if we were to exclude performance from the mix and focus specifically on the quality and note of a give exhaust, what manufacturer / design is best? I mean, does one company produce a more natural sounding, better built exhaust than others. I have been looking for a while now and like the UUC "Twin Silencer" for the E46 330Ci that was just released but no one can rate it yet, at least I haven't found anyone that has it.

But others... there are so many choices here and though science plays a HUGE part in the note (flow, resistance, backpressure etc.), the manufacturer plays as much in the quality (metal choice, weld quality, etc.) but it is all so subjective. What to do?

VinceTopasBlau3,

Does the Eisenmann system eliminate the resonator or is that only a UUC feature? Will you post a link to the exhaust you speak of, please?

BTW this is a great and useful thread! TIA

My Eisenmann system is from cat-back which eliminates the resonator. $555 or $566 (one of those numbers) shipped from Bekkers to me. I know, it's like $40 cheaper than UUC if they provide FREE shipping. But...like I said, I am very particular about being made in Germany thing.

Eisenmann site (not in english)
http://www.eisenmann-technik.de/

this is the connecting pipes from cat-back:

this is the muffler:



My Eisenmann Reivew:

http://people.we.mediaone.net/vpwseah/eisenmann.htm

Originally posted by LilEccentricJ
VinceTopasBlau3,

Does the Eisenmann system eliminate the resonator or is that only a UUC feature? Will you post a link to the exhaust you speak of, please?

BTW this is a great and useful thread! TIA

Very nice... looks like that one could make it to the top of my list! Thanx for the info....

BTW, sound files anywhere do you know? I'll check Bekkers.

well most Eisenmann sound files out there are from the M3 system. I have a link from my review page. Another file I discovered recently is from
http://www.turnermotorsport.com/catalog/exhaust.htm

Good luck!

Originally posted by LilEccentricJ
Very nice... looks like that one could make it to the top of my list! Thanx for the info....

BTW, sound files anywhere do you know? I'll check Bekkers.

Originally posted by VinceTopasBlau3
... If you just replace the muffler, you probably won't feel much of a difference. I can bet with you with the data from the Dynometer on this. But if you remove one of the obstacles (e.g. resonator or cat), you WILL feel a slight boost. Most ideal system? remove the headers, resonator, cat and muffler. Have the exhaust directed from where the engine is located.

I see a potential problem with just dumping the exhaust from the headers (aside from it being dirty and hella noisy; a buddy was doing this on a RX2...).

Part of what allows volumetric efficiency over 1.0 to occur on a atmospherically aspirated (no turbo/blower) engine is what's called scavenging, which is the ability of properly timed exhaust pulses in properly engineered (length, diameter, etc. ) exhaust system to create a vacuum in the exhaust tract of another cylinder at the junction of the header in a different part of the Otto cycle, thereby helping to not only suck exhaust out of that other cylinder, but also help suck air into it.

Barring a dragster or some other extreme application, scavenging can play a significant part in engine efficiency.

ah-ha! I see that someone has returned from the holidays! ;P

Well, yes, the concept of scavenging was mentioned in the book too. Gosh..now I really wished I had that for a good read before bed.

Some other interesting topics include intake air temp, pressure, humidity and of course the idea of "Ram-air". Pros and cons of driving air from below bumper (DINAN?) and from hear engine hood (ECIS?).

Originally posted by Kaz


I see a potential problem with just dumping the exhaust from the headers (aside from it being dirty and hella noisy; a buddy was doing this on a RX2...).

Part of what allows volumetric efficiency over 1.0 to occur on a atmospherically aspirated (no turbo/blower) engine is what's called scavenging, which is the ability of properly timed exhaust pulses in properly engineered (length, diameter, etc. ) exhaust system to create a vacuum in the exhaust tract of another cylinder at the junction of the header in a different part of the Otto cycle, thereby helping to not only suck exhaust out of that other cylinder, but also help suck air into it.

Barring a dragster or some other extreme application, scavenging can play a significant part in engine efficiency.