My exhaust setup

[equate975]

We have having a nice break in the weather so far. So I brought the m3 home.

I got my exhaust parts in, hopefully they will get installed on friday.

I am going to run two 2.5 pipes to a dual in/out muffler, with two magnaflow cats

[MR 325]

Badass, let is know how it turns out. Gonna run any tips?

[equate975]

Nope, tips are for pussies! and I cant find any I like....

I will get some pics tommorow when it gets welded up!

[xLibelle]

you got that stuff fast...

[NC325iC]

dont be gay put some damn tips on it

[equate975]

FUCK

The guys that were going to do it said their bender cant make the bends to clear my subframe.

So I went to every shop. Most of them wont even look at my car because its a BMW, apparently BMWs are magical and for some reason you can't get a custom exhaust made.

I found ONE place that could do it, and he said 2.5 is going to be a bitch, its going to hang down waaay to low, and it would cost about $600 to get it done. I talked to him for a bit and we decided to run dual 2.25 pipes, he said it would be a lot easier.

Now I gotta get rid of this 2.5 stuff somehow, this is the last time I dont listen to jordan damnit!

[325Projectz]

I had that exact setup on my car. Same muffler, same cat x 2, but I had a H pipe put in, it cleaned the sound up alot.
Devon was saying something about selling the exhaust, contact him.

That exhaust shop is crazy, there is plenty of room, shit I got a 3in hanging below my slammed car. And $600 , I had mine done for $200.

[equate975]

Yeah, my buddy says he can build it for me. I might see if he can. He has welded up his own turbo headers so I would trust him to be able to do it.

[Budget Beater]

why in the world are you running dual in and out ehxaust that large? you will lose alot of low end torque due to lack of back pressure.

[Insanity]

why in the world are you running dual in and out ehxaust that large? you will lose alot of low end torque due to lack of back pressure.

Behold, for I am about to rip you a new one for being a retarded scrub (as if we didn't already know)...

Backpressure is NEVER good. Ever. Backpressure is a positive pressure pressing against your exhaust port.

What's the point of your exhaust system? To fully evacuate exhaust in the fastest way possible, so you don't have any left in your cylinder.

What would a positive pressure acting against the port do for you? Abso-fucking-lutely nothing. In fact, backpressure is one of the WORST things to have in an exhaust system. Go plug up your pipe with a potato and feel all the torque you gained. Heh.

The reason why you need to select a piping diameter equivalent to the maximum CFM of your engine is because of something called the venturi effect. The higher the velocity of a fluid, the lower pressure there is across that fluid. Therefore, the faster your exhaust is travelling, the LOWER the pressure is across your exhaust port, and therefore the BETTER your cylinder can evacuate. Note that this is the opposite of backpressure.

Now, in a bigger pipe, velocity is lower. Sometimes. Obviously if you have way too small of a pipe for the CFM, your exhaust will become a pressure-causing restriction until the pressure of the stream rises to a point where it can continue to flow, and subsequently your velocity will also decrease.

Therefore, VELOCITY is what matters, because it produces NEGATIVE pressure. BACKPRESSURE is NEVER EVER EVER EVER good for anything. Ever. A bigger pipe will have HIGHER velocity and lower backpressure (probably negative) at higher CFM levels due to the restrictions of the smaller pipe.

Consider yourself educated.

[MrK]

pwnd

[xLibelle]

surrounded by idiots

[equate975]

surrounded by idiots

x2


You need SOME back pressure or like budget beater said, there will be no torque. I run my car open headers now, it runs like complete shit. If I stomp the gas it just gets "stuck" of sorts because there is no backpressure working for torque. By your logic having open headers would be the ultimate exhaust, and its not.

Anyways, 2.5 I think will be fine, its going to be a bit big and I might lose a little torque but it will give me more room to play with for future mods.

[MrK]

equate975/Budget Beater

I'd like to see you back up your claims.

I bet you'd like to see me back up mine that backpressure is BAD:

http://auto.howstuffworks.com/muffler5.htm

[equate975]

Hmmm, I am wrong.

Not that, that how stuff works autually proved anything, but I googled a bit.

Seems to be a general misconception about backpressure vs. velocity

Insanity is correct, however there is such a thing as too big of an exhaust.