[SoCal Supreme]

Does anyone have it? Also, are there any cool carbon fiber diffuser's for the M-tech rear bumper that do quad setups?

[AMT92]

your gonna lose a ridiculous amount of power with straight piping, not to mention the cost and the added weight, and in all honesty it might sound like shit.

[AMT92]

Originally Posted by e90David

how do you lose power? i thought the muffler/resonator weighed more than just piping

Loss of backpressure on a NA car will make you lose torque and with the extra piping and welding to make quads it'll add weight just for a look, and the sound...ehhh.

[TommyK]

i dont know any one who has. i think the muffler and resonator are prob near 60 pounds together, i couldnt see it weighing more by doing that extra pipe work if you delete the others. pluss you would have to scrap the storage area in the trunk to do all of that.

about the rear bumper, longtran put a great looking diffuser on a 335 w/ mtech and put the new LCI diffuser on the back and i thought it looked pretty good. check out his website ltbmw.com and click on the blog, its the SG 3rd picture down. you might have to get smaller sized pipes to do quads though.

GL on this, id love to see it happen

[AMT92]

Originally Posted by e90David

i don't think you know what backpressure is

i just know without it NA lose torque

feel free to correct me

[im spencer]

Originally Posted by e90David

meh i don't feal like searching through all of the bullshit on this forum again

i searched lol

http://www.e90post.com/forums/showth...re+torque+loss

all i know is that my car pulls a lot harder around 3k rpm with the little things i've done to it

This is the article you speak of:

Some say that "an engine needs backpressure to work correctly." Is this true?

No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.

The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.

The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.

The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.

Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.

Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.

[bavpower]

i did a muffler delete only,, and had a 3" pipe installed to replace the muffler. the weight reduced in that was a good amount. i felt the weight of both and was significantly less. that answers any weight questions. as far as power goes there is no loss in power y do u think any race modified cars have strait pipes. turner motorsport built a 328i touring car and installed strait pipes. check it out that car is awesome. back to the topic it did gain a few hp. and after i had that work done i installed an injen intake. then dynod the car to see where it was. well with those 2 mods i am running 198hp to the rear wheels, and 189 tq to the rear wheels. also the weight reduction helps on acceleration and handling especialy around conrners there is less weight in the rear and you can feel that. def do a muffler delete idk about cat delete the sound with the muffler delete is amazing, the cats will make it obnoxiously loud. at crusing speed u can barely hear them inside the car, when accelerating it sounds awesome its deep. ive been asked several times what exhaust i have on the car.

[dvpouldar26]

With a muffler delete on a N/A car, you will lose a small amount of low end torque, but gain a little high end hp. Even if you delete the mufflers, secondary cats, and resonators, you still will have some backpressure from the primary cats.
The reason people say that having a straight pipe is bad is because the effect it has on your valves and valve seats. On FI cars, the objective is to get the air out of the combustion chamber out as quickly as possible. With turbo cars, backpressure holds back the turbine on the hot side of the turbo. A straight pipe is the best option because there is no backpressure holding the turbine back, thus it can spool up quicker. This isnt true for NA cars.

In NA cars, backpressure is needed for an engine to work. An IC engine is a large air pump. During valve overlap, the exhaust cam and intake cam make the intake valve and exhaust valves open at the same time. Engines are designed with valve overlap in order to gain some low end torque. Valve overlap creates a vacum in the combustion chamber which will suck in a fresh air charge in for the next stroke. When there is no backpressure, there is nothing holding this new charge back inside the combustion chamber, so it gets sucked out because of the lack of backpressure. Now, the cylinder leans out, which causes to burn a valve and to burn your valve seats because this air charge is being sucked out of the combustion chamber. That is why low end torque is lost.

IMO, if only doing a muffler delete, no harm can be done because there are other things in the exhaust system that provide backpressure such as primary cats, secondary cats, and resonators. I wuoldnt recommend a straight pipe all the way from the headers back though, except on FI cars.

[JaysBlueE92]

i'm also running a muffler delete on my e92 with just 2 3/4" piping and quad tips from cyba installed. I may add a muffler to the section just because I get some(not a lot) droning at 50 -65mph. Although it may be in my head When driving in DS especially, I honestly do not feel any loss of power.

[AMT92]

im spectical about it, i dont wanna lose any torque considering the 330 doesnt have much torque to begin with