I know nothing about exhausts...

[Febi Guibo]

(I think I have a good understanding of exhaustion, however...)

ok, I don't know squat about exhausts, tuning exhausts, etc. etc. I have had stock exhausts on every car I've owned with the exception of a custom exhaust system that was recently on my M42 (2.5" pipe, magnaflow muffler, magnaflow cat with no resonator).

I *hated* the setup. As you have probably guessed, it was way too loud for my fuddy-duddy tastes (it drowned out NPR on the radio) but more importantly, I'm not sure exactly what it was doing for the car's overall performance.

At WOT, I'm reasonably sure the setup boosted performance; I'm know any car engine is basically like an air pump, and (I suppose) the more air that can move out of the engine, the better... at the same time, I felt like I was driving a bi-plane.

It was really really loud, which did have it's thrilling moments... mothers pulled their children away from the curb when I drove by. Guys on motorcycles would turn and point... When I'd cruise Rice Vegas (I live near chinatown) I had a few envious looks from the dudes in their honduhs.

But... at PART THROTTLE, the system was wildly inconsistent... sometimes it sounded quiet, sometimes sounded good, and sometimes... sounded like... well, like ass.

(please excused the following wildly, probably inaccurate subjective observation) It sorta sounded like... sometimes air would flow very smoothly through the thing, and other times, there was just a ton of air hanging out in the system.

for example... say I'm doing around 75 mph at around uh 3600 rpm... the exhaust sounds terrible (un-natural gurgling, etc. etc.) ...I downshift to 4th, speed up to say, 85 (4000rpm-ish), there's a rasp, a loud long farting or whatever (not me, the exhaust), and then put it back into fifth, back to 75mph, and... the exhaust sounds great! kinda nice actually! What gives?

sooo... if anyone with an engineering background or a lot of experience with aftermarket exhausts (eg, everyone else on this board except me) can chime in, I await yer knowledge and insight.

thanks!

[FL318is]

Mine has an aftermarket something on it. I don't like it so I will probabably go to stock. If you search www.e46fanatics.com I am sure there is a thread on there. They are always throwing on exhaust mods.

[Tonyb]

How old is the the muffler? Might be worn out inside.

[Febi Guibo]

the muffler is brand new (I have since put a stock exhaust back on the car)

what I'm asking about, really, is how to exhaust systems work in general...

eg, why would my exhaust (or an exhaust, in general) sound terrible at one speed/rpm, and then, after speeding up and slowing down... sound fine again?

I know there's like, a more scientific answer, but... science scares me! :)

[asubimmer]

I really don't know but its has to do something w/ the velocity of the gases going through the muffler I would think. There also could be some variables like if there is any gas left going through the exhaust, like if you are running a little rich. Don't hold me to that sam, but at least it sounds good lol.

[BrandC]

That 2.5" piping is overkill for the output/displacement of our M42's, especially on a street car. Usually a rule of thumb is you need some backpressure on the exhaust for low end torque, and less for high end power. Maybe that's why the exhaust note change is so drastic as you near 4k RPM (where the M42 makes power), that is the changeover point?

There are only two places on the stock exhaust system that seem restrictive; the muffler and "pancake" section underneath the rear subframe (for clearance issues I'm assuming). You could probably get an aftermarket muffler and call it a day. This way you can change them easily when you aren't satisfied with the tone or noise level.

The diameter of the resonators and inner diameter of your muffler is what is going to affect sound the most, not so much as performance. You'll have to make trade-offs, that's all. Larger diameter piping/muffler: more noise, more top end power/less low end torque. Smaller diameter: less noise, less top end power, stock low end torque retained.

However, now that you have a new engine with more displacement/powerband, you're probably reconsidering what to do with exhaust now. My suggestion is you use custom 2.25" piping with at least one resonator and your muffler of choice. That diameter piping works well with anything 1.9L+ as far as noise and performance coincide.

Hope that longwinded jibberish helps.

[D. Clay]

I just bought an OEM muffler from BMA. It's twice as heavy as the last two I had on the car. It makes those OEM rear muffler hangers look like they belong there. The last two were $200 OEM type catbacks made by some aftermarket company that is sold by most of the parts houses including BavAuto. They go to junk very quickly and blow the baflles loose. They make a buzzing sound at 2400 RPM.
These cars are hard on exhaust systems. I also feel that BMW made these cars pretty quiet originally, that it's the aftermarket stuff that doesn't hold up.
And OEM is only $1500!

[Vladi]

I've currently got the M40 exhaust (both muffler and cat) with the stock 1.69'' diam. pipe. Should i leave it like this or put a bigger diameter pipe? I've got an E36 M42 '94 engine.

Thank you!

[BrandC]

1.8L-2.0L displacement engines should not be rocking more than 2.5" exhaust piping.

I think 2"/2.25" is perfect if you want the sound to somewhat match the "profile" of the car.

[silverblades181]

ive heard the supersprint cat-back is a good one. Not too loud and good gain in performance.

[Tonyb]

ive heard the supersprint cat-back is a good one. Not too loud and good gain in performance.
I have the supersprint and I love it! That was my second mod after the chip and I really felt more power. I paid 500.00$ for it five years ago and it still looks and sounds new. I also ran it without the cat and it had the same noise level, not to loud not to soft, just a mild sporty sound under full throttle and it sound like a stock system on the interstate. Anther plus is that it's the same size as stock but not as heavy. The price is a little more steep now, but you get what you pay for and I will get another one if this one goes!
I can post a pic if anyone wants to see it.

[Eurospec]

Isn't the superspring almost impossible to find new nowadays?

[Tonyb]

No it's not! I have the latest catalog from BMP Design and I was wrong about the price too! I paid 475.00 shipped and they want 495.00 without shipping cost. They have an online store where you can request a catalog or place an order.

[Vladi]

I've currently got the M40 exhaust (both muffler and cat) with the stock 1.69'' diam. pipe. Should i leave it like this or put a bigger diameter pipe? I've got an E36 M42 '94 engine.

Thank you!

Hey, i've asked something here! :confused:

[sheepdog]

Find out the stock 325 exhaust tubing size, and get ahold of a 325 muffler and cat.
Maybe try something considered a mild to medium upgrade or aftermarket direct replacement for these.

This should flow fine for what you need without being excessively loud.

[Jtuner]

What's the stock size of the m42's exhaust? When I was under my car lookin at it with the exhaust guy, I thought we agreed we thought it was around 2.25" already..?? is this right er?

[fabby318is]

Last time i measured i came up with 2" I.D.

[JDNo.5]

The stock exhaust piping is 2.25 (2 1/4) that's the size opening I needed when I purchased my magnaflow exhaust. The magnaflow sounds real nice outside of the car, but inside it whales like an out of control beast. I'm not a big fan of the sound inside the car. Does anyone have a sound clip of the supersprint exhaust on a m42? I've heard them on 325's, but the sound can be totally different with the 4 banger. As for the stock exhaust they are very very quiet, if you don't want to hear any exhaust sound that's the way to go, but I like a little rumble when I'm at wot :) .

[Jtuner]

Yeah what I want to avoid is sounding like a honda... I think I may keep the stock exhaust since it is pretty decent sized, and just put on an intake for sound.. I love the sound of my car but I don't want it to 'fart' or 'buzz',, that shit is for ricers...
If anyone knows of a muffler thats nice and throaty, and not so loud that the cops will look at me when I drive by, POST IT!!

[sheepdog]

Yeah what I want to avoid is sounding like a honda... I think I may keep the stock exhaust since it is pretty decent sized, and just put on an intake for sound.. I love the sound of my car but I don't want it to 'fart' or 'buzz',, that shit is for ricers...
If anyone knows of a muffler thats nice and throaty, and not so loud that the cops will look at me when I drive by, POST IT!!

You could try what I did.
Cut out most of the front and fenderwell side of the stock intake, sounds really good.

[fabby318is]

Sheepdog, could you please post a pic of your air box or give me a little more detail on the dimensions of the cut out?

Thanks a bunch,
Fabby

[bullmand]

Does anyone have a sound clip of the supersprint exhaust on a m42? I've heard them on 325's, but the sound can be totally different with the 4 banger. .

This is my 318ti (M44) with the Supersprint cat-back. I would expect the M42 to sound very similar.

www.putfile.com/bullmand

BTW, please excuse the crappy quality. That was recorded with my still camera.

[Jtuner]

Oh dear god that sounds sweet :D That's exactly the sound that a bmr should make!! So Supersprint seems like a good choice lol I heard clips of the stromburg(??) i think it was, exhaust, and that sounded pretty sweet on a ti.. I don't see where people get off by saying that the magnaflow and dynomax mufflers have a comparable sound to this supersprint and the stromburg.. I've heard those cheaper mufflers and guess what,, sounds like a damn honda......

[Berlin]

sounds nice, how high did u rev it there

i too am looking for a quiet civilized exhaust, one that upholds the good name of my car... as unfortunatley the po had little understanding of just what a roundel really is

sheepdog, i dont think it will be easy to install the 325 exhaust because of the tip... how its slanty and all... one of the sexiest sounding engines is the M20 i think so i wonder how that system will make an m42 sound http://www.e30tech.com/forum/images/smiles/eusa_think.gif

[bullmand]

Yeah, I've had that exhaust for about 6 years now and I've been very happy with it. The only down side is the cost. I got an unrepeatable smokin' deal on mine, so I can't complain, but I'd hate to have to replace it. Berlin, that was up to somewhere between 4 and 5K I think. The engine wasn't very warm so I didn't want to go crazy.

[sheepdog]

sounds nice, how high did u rev it there

i too am looking for a quiet civilized exhaust, one that upholds the good name of my car... as unfortunatley the po had little understanding of just what a roundel really is

sheepdog, i dont think it will be easy to install the 325 exhaust because of the tip... how its slanty and all... one of the sexiest sounding engines is the M20 i think so i wonder how that system will make an m42 sound http://www.e30tech.com/forum/images/smiles/eusa_think.gif

I am saying just use the muffler and cat. Not the entire exhaust system itself.

[Berlin]

yaya i get it, its just that the cat is really different and the downpipe into it aswell, so youd be better off using our cat but then it only has one output and the 325's muffler has 2 inlets

[JDNo.5]

This is my 318ti (M44) with the Supersprint cat-back. I would expect the M42 to sound very similar.

www.putfile.com/bullmand

BTW, please excuse the crappy quality. That was recorded with my still camera.

WOW :eek: , that's what an aftermarket exhaust is suppose to sound like. Man, if you were working for Supersprint you just closed a sale...

DOH at least an 8 week backorder on the Supersprint for the M42... DAM, why must all the stuff I order for this car be on backorder??? :mad:

IE3 Flashbacks… DOH!!! :D

[dude8383]

WOW :eek: , that's what an aftermarket exhaust is suppose to sound like. Man, if you were working for Supersprint you just closed a sale...

DOH at least an 8 week backorder on the Supersprint for the M42... DAM, why must all the stuff I order for this car be on backorder??? :mad:

IE3 Flashbacks… DOH!!! :D

it'd be nice to hear it approaching redline..

[m42 fan]

(I think I have a good understanding of exhaustion, however...)

ok, I don't know squat about exhausts, tuning exhausts, etc. etc. I have had stock exhausts on every car I've owned with the exception of a custom exhaust system that was recently on my M42 (2.5" pipe, magnaflow muffler, magnaflow cat with no resonator).

I *hated* the setup. As you have probably guessed, it was way too loud for my fuddy-duddy tastes (it drowned out NPR on the radio) but more importantly, I'm not sure exactly what it was doing for the car's overall performance.

At WOT, I'm reasonably sure the setup boosted performance; I'm know any car engine is basically like an air pump, and (I suppose) the more air that can move out of the engine, the better... at the same time, I felt like I was driving a bi-plane.

It was really really loud, which did have it's thrilling moments... mothers pulled their children away from the curb when I drove by. Guys on motorcycles would turn and point... When I'd cruise Rice Vegas (I live near chinatown) I had a few envious looks from the dudes in their honduhs.

But... at PART THROTTLE, the system was wildly inconsistent... sometimes it sounded quiet, sometimes sounded good, and sometimes... sounded like... well, like ass.

(please excused the following wildly, probably inaccurate subjective observation) It sorta sounded like... sometimes air would flow very smoothly through the thing, and other times, there was just a ton of air hanging out in the system.

for example... say I'm doing around 75 mph at around uh 3600 rpm... the exhaust sounds terrible (un-natural gurgling, etc. etc.) ...I downshift to 4th, speed up to say, 85 (4000rpm-ish), there's a rasp, a loud long farting or whatever (not me, the exhaust), and then put it back into fifth, back to 75mph, and... the exhaust sounds great! kinda nice actually! What gives?

sooo... if anyone with an engineering background or a lot of experience with aftermarket exhausts (eg, everyone else on this board except me) can chime in, I await yer knowledge and insight.

thanks!


I just found this thread (missed it during my move before), and I'll try to throw in my .02 on this subject.

First, as has been said, BMW engineered the origional exhaust system quite well, ballancing all of their requirements nicely. It's quiet, doesn't take up more space than necessary, and doesn't rob too much power.

Most people will replace their exhaust for one of three reasons: 1) it's worn out (rusted, etc...) 2) they're looking for a performance improvement or 3) they're looking for a different sound. As far as those reasons go, #1 is totally legitimate. #2 may be legitimate, but you are really wasting your money when there are much bigger gains to be found elswhere on anything close to a stock motor. #3, well, I guess if you have a couple hundred extra dollars to throw away, whatever.

OK, now that that's out of the way, let's get into how the exhaust works. Lots of times ( and in this thread as well) people will tell you that you need "Backpressure" that can be gained by using a stock (relatively small diameter) pipe to help with low end torque. They are getting to the correct answer, but their science is flawed. You will absolutely hurt your driveability and performance if you go larger than 2.25 on the street, but the reason is due to scavenging effects. When you use the correct diameter pipe, the exhaust must increase velocity as it travels through the exhaust system. As it speeds up, it will help create a slight vacum on the ehaust port at the cyllinder head. When the next exhaust valve opens, the vacum "sucks" the exhaust out, allowing more air to enter the cyllinder during the next intake stroke. When you increase your pipe diameter, the exhaust velocity slows, you don't get the vacum, and you actually will lose power, compared with the smaller pipe.

As a side note, this is the exact reason that V type engines with dual exhaust incorporate a ballance "H" or "X" pipe. The crossover enables better scavenging.

So, what is the best type of exhaust for any particular car? That's a question better suited for an engineer, not a criminal justice major. All I know is that it depends on a lot of different factors, including the size and type of engine, and the desired rpm range of your powerband.

Febi, to answer the part of your post regarding the strange sounds coming from your exhaust, the main reason is that you have an exhaust that does not match up to your engine at all. When you get systems that don't work together, you can get strange harmonic frequencies at different rpm ranges, and that's what you're encountering.

Bottom line: Those German engineers knew what the heck they were doing. If free power was as easy as slapping on a bigger pipe, our cars would come from the factory with huge ricer exhaust systems.

Here's my recommendation for a (fairly) cheap exhaust that will not sound bad, and will give you as good power as anything: 2.25 inch pipe, with either a Dynomax Super Turbo muffler, or a Summitt Turbo muffler. any exhaust shop can hook you up with the pipes for cheap. I have experience with both of the aforementioned mufflers, and would recommend either. Both are slightly louder than stock, but not so much that small children will cower in fear. More importantly, both work well and are inexpensive.

OK. Long post. Hopefully I've answered some of your exhaust questions and cleared things up a little bit.

Brian