exhaust options

[matt]

bud, you are a little confuseled

1. NA cars need not backpressure, but scavenging effect (search)
Factory tuned scavenging effect is tuned for low rpm and thus increases the volumetric efficiency at lower rpms (it's all about taking advantage of resonance)

2. freer flowing exhaust will increase overal volumetric efficiency due to lack of backpressure, but will also alter the resonance frequency that the stock exhaust was tuned for (to high rpms), that's why you loose torque down low with bigger pipes but gain up top

3. the OEM EMS is designed to adjust to changing VE to an extent (i heard a figure of 5-10% somewhere) by means of measuring the flow of air through MAF. But, if you will search hard on bf.c, you will find a post by JimC himself where he says that one would definitely need a retune if the exhaust system is significantly changed. (most likely refering to m5x engines with factory EMS with his own chips inside). Which is proven on practice by my salt-n-pepper'ed sparkplugs, JimC chip and a very-free flowing exhaust. So i wouldn't rely just on MAF, motronic and narrow band for AFR correction with significant mods.

Alex

:up:

I am sooooo glad somebody is paying attention.

[static]

Why will he lose power down low? due to loss of back pressure? FALSE

"Modern BMWs don't have to worry about the effects described above, because the DME (car's computer) that controls the engine will detect that the engine is burning leaner than before, and will adjust fuel injection to compensate. So, in effect, reducing backpressure really does two good things: The engine can use work otherwise spent pushing exhaust gas out the tailpipe to propel the car forward, and the engine breathes better. Of course, the DME's ability to adjust fuel injection is limited by the physical parameters of the injection system (such as injector maximum flow rate and fuel system pressure), but with exhaust backpressure reduction, these limits won't be reached.

- Adapted from Thomas V."

-uuc motorwerks

bud, you are a little confuseled

1. NA cars need not backpressure, but scavenging effect (search)
Factory tuned scavenging effect is tuned for low rpm and thus increases the volumetric efficiency at lower rpms (it's all about taking advantage of resonance)

2. freer flowing exhaust will increase overal volumetric efficiency due to lack of backpressure, but will also alter the resonance frequency that the stock exhaust was tuned for (to high rpms), that's why you loose torque down low with bigger pipes but gain up top

3. the OEM EMS is designed to adjust to changing VE to an extent (i heard a figure of 5-10% somewhere) by means of measuring the flow of air through MAF. But, if you will search hard on bf.c, you will find a post by JimC himself where he says that one would definitely need a retune if the exhaust system is significantly changed. (most likely refering to m5x engines with factory EMS with his own chips inside). Which is proven on practice by my salt-n-pepper'ed sparkplugs, JimC chip and a very-free flowing exhaust. So i wouldn't rely just on MAF, motronic and narrow band for AFR correction with significant mods.

Alex

[matt]

Sigh.

[So Live]

Why will he lose power down low? due to loss of back pressure? FALSE

"Modern BMWs don't have to worry about the effects described above, because the DME (car's computer) that controls the engine will detect that the engine is burning leaner than before, and will adjust fuel injection to compensate. So, in effect, reducing backpressure really does two good things: The engine can use work otherwise spent pushing exhaust gas out the tailpipe to propel the car forward, and the engine breathes better. Of course, the DME's ability to adjust fuel injection is limited by the physical parameters of the injection system (such as injector maximum flow rate and fuel system pressure), but with exhaust backpressure reduction, these limits won't be reached.

- Adapted from Thomas V."

-uuc motorwerks

[matt]

I'm just going to be matching ID pipe with the ID of the collectors on my headers. So I will be running dual 2.25" back to a Dynomax I have laying around.

And you will have an exhaust that's twice as heavy as it could be, and will probably cost you power down low.

[87-325ic]

A single 2.5 inch seems to be the best option, or at least i want it to.

are there muffler options for this with a non-straight-through design that sound decent?

dual 2.25+ just seems like too much piping.

i will have the s52 headers on it, and that is probably it, i will need to piece the rest of it back from there.

help me out please.

[So Live]

i was thinking dual 2.25 but it seems pretty huge. cross-sectionally speaking its bigger than a single 3". Alot of people rock the 3 for turbo set ups. i dont know...

[PiercedE30]

I'm just going to be matching ID pipe with the ID of the collectors on my headers. So I will be running dual 2.25" back to a Dynomax I have laying around.

[bimerok]

I had the same fear, but I just installed Vibrant straight through muffler (glass packed) and to my surprise it is not loud at all. It has nice deep tone to it.

I have s50 with s50 headers and mid-pipe, connected to Vibrant straight through 2.5" dual-in/dual-out.

The best part is that the muffler was only $130

[BigD]

They are wrong automatically writing off straight through mufflers, I have 2 Borla's on mine and it doesn't drone at all. Quiet when driving and loud when I get on it.

I hope you're right. My setup is OBDII headers, OBDI midpipe, UUC RSC36. I'm kinda stoked about it, I think it's going to sound orgasmic.

[So Live]

What are the rest of your specs? what size piping? single or dual? headers or stock manifolds?

Just looking at some e36 M catbacks, UUC and IE's are 2.38" dual pipes. if 1 2.25 pipe is optimal, why do these guys make dual 2.38 pipes? Its pretty obvious to see what flows better(more)

[cheades]

They are wrong automatically writing off straight through mufflers, I have 2 Borla's on mine and it doesn't drone at all. Quiet when driving and loud when I get on it.

[So Live]

Do you guys think dual 2" is too much? I hear matt saying run single 2 1/4 but i like the dual pipes. The ability to run x/h pipes should help with the rasp.

Also, you guys dont reccomend running a magnaflow, what about something like a flowmaster 40 series or something? Is a chambered muffler really going to kill my performance?

[asubimmer]

it might not be bad matt. Muffler placement has more to do w/ the sound level and rasp level than the actual muffler imho. I am running a single 2.5" all the way back w/ just a glasspack inbetween the seats and then a cheapo cannon on the back. It sound great and its loud but not more than a triflow catback.

[static]

And it's loud as hell.

yes!, i was gonna say

whatever he means by "sufficient". Sufficient for the engine? or sufficient for the humans near the engine?