[S_M]

Originally Posted by ilia@industry

Guys, back pressure does not create torque. It's a common misconception. Back pressure does nothing useful for power or torque.

Amen, someone knows something. Backpressure is the last thing you want in any car, it is completely the wrong term. Anybody that tells you an exhaust creates backpressure has no clue what theyre talking about.

Exhaust velocity is what youre dealing with. The size and flow of the exhaust determine the velocity, along with other factors... NOT backpressure...

[IND-Distribution]

Right, it's a compromise between exhaust gas velocity, and exhaust gas volume. The idea is to flow as much volume as possible (big piping), but also to maintain the highest possible velocity (skinny piping). That leads to a compromise, usually set for an ideal RPM, which usually coincides with peak volumetric efficiency, which usually coincides with torque peak.

[jjhan85]

Originally Posted by ilia@industry

Guys, back pressure does not create torque. It's a common misconception. Back pressure does nothing useful for power or torque.

yea thats what i thought. I mean if you think about it the air flow is going out and why would you want air flow to be resisted or why would you WANT back pressure? ( plus the word doens't sound psotive at all for a cars performance in my opinion ) i never understood why people are saying that ... hmm ...i guess its a tricky topic, still don't quite FULLY understand it yet

[koreez88]

Well then, does that mean that muffler delete has no negative effects on torque/hp?

[Excellence]

So basicly this loss in torque is all my imagination?

[hl0m4n]

Originally Posted by Excellence

So basicly this loss in torque is all my imagination?

so if a person tells you installing a cat back exhaust with metallic cats has backpressure their wrong? im a bit confused.

if you have a catback with no metallic cat its just a straight pipe thus no back pressure and essential better for the turbos for relief no? just a bit bad for the enviornment.

[ScheerSpeed]

well to tell you the truth, im used to 2-sroke engines in karting, and i know they need backpressure in order not to overheat and spit gas out the back. but remember, we have N/A motors on our 325/328 that we are doign the muffler delete to, not a 335. i know on a turbo engine it is best to get as much in and out as possible, but i know its not the same on a N/A...

[S_M]

Originally Posted by hl0m4n

so if a person tells you installing a cat back exhaust with metallic cats has backpressure their wrong? im a bit confused.

if you have a catback with no metallic cat its just a straight pipe thus no back pressure and essential better for the turbos for relief no? just a bit bad for the enviornment.

Backpressure is your enemy on ANY car, be it forced induction or naturally aspirated, no car needs nor wants, backpressure.

What a car DOES need is exhaust velocity, which is directly related to the diameter and design of the manifold piping, head design, and exhaust design. Most people don't know the difference or don't understand the difference and they simply toss "backpressure" around as the catch phrase.

[hl0m4n]

^ thanks. if you look at the eisenhaus or supersprint full exhaust setup minus downpipe compared to stock, the new exhaust not having the metallic cat further removes/limits backpressure no? thus running catless is better but a down on the enviornment.

[Excellence]

Okay. So can someone tell me the truth. Does removing your muffler cuase you to lose torque? If so, how can I improve the amount of torque by modifying my straight pipe? I was thinking of adding a mesh.

[ScheerSpeed]

mesh would restrict the flow, not create backpressure if anything...

[nimo]

Originally Posted by reallyslow

Amen, someone knows something. Backpressure is the last thing you want in any car, it is completely the wrong term. Anybody that tells you an exhaust creates backpressure has no clue what theyre talking about.

Exhaust velocity is what youre dealing with. The size and flow of the exhaust determine the velocity, along with other factors... NOT backpressure...

I thought back pressure was part of the tuning process of the engine combustion\ignition\timing. If back pressure is the last thing I want in a car, wouldn't it be nice to just unbolt the exhaust manifold/header from the cylinder head. However, BMW designed the exhaust system to meet emssions and for fuel efficiency.

"Backpressure is necessary at lower RPMs to make the most efficient
cylinder filling. At TDC there is some overlap as you change from
the exhaust stroke to the intake stroke. At this point, an exhaust
which has too little backpressure will allow some of the incoming
fuel-air mixture to escape out of the exhaust, effectively leaning
the mixture. (It ain't real good for emissions, either.) This effect
is decreased as RPMs increase since each stroke occurs faster."

I do think though that the muffler delete does affect your low end. And having some back pressure at low engine speed is necessary to have a linear power curve.

Off the topic: My regular poop looks like a cigar. If my anus had a larger diameter then my poop would come out like a buckshot; since there is less back pressure. I'll stay with my cigar poop since I don't like cleaning the toilet.

[Excellence]

WOOOOOOH. Added a simota and man the car feels like its got power!

[tabs]

hey. ive been following all the muffler delete threads and I did this mod,
however im certain that I have lost low end torque.
I dont know how to remedy this, did adding the simota make it better than stock condition or did it just cover the lost torque from the muffler delete mod.

How does the car feel now with the simota?

[StarrDlux]

the turbo itself is more backpressure than the sum of the exhaust system. so it is in your head.

Even when the wastegate is fully open there is more backpressure than you can shake a stick at.

they use vanos to burn a little gas at cold-boot to light the cat's fast. the exhaust flap is to ensure you don't hear the car make american noises lol.

exactly when does anyone (AT6) drive around less than 2000 rpm? that would be never at the speeds (80~mph) people drive on the freeway (55mph) here in the ATL.

can you even achieve that low rpm with a MT6 tranny?

peak performance of turbo chargers is based on pressure differential The delta of the pressure before the turbo and after is mainly what counts.

It is interesting they didn't put the wastegate far closer to the cat's if their goal was to light them off faster or create torque.

[Malek@MRF]

Originally Posted by BoostedBMW

I was always under the impression that resonators didn't create backpressure, they just reduced rasp.

Straight through resonators do not induce ANY backpressure unless they are "louvered".

Resonators do not quiet down the exhaust either, they are what they are, resonators. They change the exhaust note. Resonators are used to tune and control the sound of the exhaust. If you want to tone down the exhaust, use a straight through muffler.

As for the backpressure argument, this car is turbo'd. Backpressure is a turbo engines enemy. Yes it is true that an overly free-flowing exhaust is sometimes an issue with spooling up the turbo's, but thats generally a downside that is attributed to medium to large frame turbo's. The exhaust piping of the 335 is 2.5" on each side (which is very ideal) and the turbo's are very small.

To the original poster:
Your car is not any slower with the muffler delete. The fact that it's louder makes your car seem slower to you. I am willing to pay for your dyno run just to help clarify it. A choked up turbo exhaust=loss of torque. This is not your issue here.

[Malek@MRF]

Originally Posted by ScheerSpeed

mesh would restrict the flow, not create backpressure if anything...

restricting flow is creating back pressure.

[StarrDlux]

you could restrict flow on the intake side (creating more intake velocity) to generate more low end torque to spool the turbo's up faster but these puppies are like AAA mosquito bite sized titties so many tricks aren't necessary.

i'd still love to see a BT AT6 with a stall

[Sam12345]

i am lost!
so does this mean doing a muffler-delete on a e92 335 would make you loose low end power but gain high end?
or wtf!

[Malek@MRF]

Originally Posted by Sam12345

i am lost!
so does this mean doing a muffler-delete on a e92 335 would make you loose low end power but gain high end?
or wtf!

No, thats not what this means.

The muffler delete doesn't cost you power by any means.

[Sam12345]

Originally Posted by Malekreza11

No, thats not what this means.

The muffler delete doesn't cost you power by any means.

oh i see. alright cool.
thanks once more!

[AllEyesOnMe]

Originally Posted by Malek@MRF

Straight through resonators do not induce ANY backpressure unless they are "louvered".

Resonators do not quiet down the exhaust either, they are what they are, resonators. They change the exhaust note. Resonators are used to tune and control the sound of the exhaust. If you want to tone down the exhaust, use a straight through muffler.

As for the backpressure argument, this car is turbo'd. Backpressure is a turbo engines enemy. Yes it is true that an overly free-flowing exhaust is sometimes an issue with spooling up the turbo's, but thats generally a downside that is attributed to medium to large frame turbo's. The exhaust piping of the 335 is 2.5" on each side (which is very ideal) and the turbo's are very small.

To the original poster:
Your car is not any slower with the muffler delete. The fact that it's louder makes your car seem slower to you. I am willing to pay for your dyno run just to help clarify it. A choked up turbo exhaust=loss of torque. This is not your issue here.

I'm up for this if you are haha.

I just got a muffler delete on my M235i and it seriously felt like my car doesn't have the strong pull in low end anymore, but rather a more linear, subtle pull......