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      08-01-2011, 04:30 PM   #1
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- The Official Please Explain an Exhaust in Full Detail Thread -

Okay so this seems to be a topic most people keep covering again and again, I myself am still lost in the foreign language of 'exhausts'.

Could someone please provide a detailed description of how exhausts work, I'm not talking about how they help with air flow and increasing hp/tq's. I'm talking more of how to actually GET the most hp/tq's, what does it mean to have 4 resonators over 2? What would be better an x-pipe or a y-pipe? What's the difference between a cat-delete and having high flow cats, why members choose one over the other? 200 cels, 400 cels or whatever all that actually means?

Also... How do you get the best possible sound, yes I'm talking 'loudness' and 'refinement'.. For instance would you get a better sound having 4 resonators with a cat-delete, or 2 resonators with high flow cats at a 300 cel or the opposite way around..

Last thing; I know you would have to get a tune to utilize maximum gains on all mods installed on a car but would these gains be higher than the ones that are generally provided on manufacturers website or the 'same'.

I know there are a lot of questions posted in a huge mix up but I'm sure you guys can get the general feel of what I'm trying to get answered.

Thanks
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      08-02-2011, 12:01 PM   #2
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^^^I think thats a great question. Hopefully someone will take the time to explain to the n00bs.
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      08-02-2011, 12:16 PM   #3
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      08-02-2011, 12:19 PM   #4
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im going to answer some the best way i can...

resonator = reduce the sound of the exhaust/muffler the more resonator the less annoying your car will be... also reduces rasp.

HFC = its less restriction compare to OEM meaning more air flow. less honeycomb. (smells)

Cat Delete = free flow. no air restriction more power (smells like shit)

200 cel or 400 cel = OEM cat has 400 cel HFC usually has 200 Get the idea? MORE FLOW, LESS FLOW

x pipe or Y pipe = the M3 has X pipe not a Y (cant really explain how this works) lazy on googling)

NOW the sound when you mix and match the resonator and cat it will sound loud depending on your exhaust.

with no cat and resonator your exhaust will be so FREAKIN LOUD. Now that being said adding HFC or resonator will reduce the rasp, and the sound of your exhaust.


EDIT:

Also when selecting exhaust pipe from stainless steel or titanium the exhaust sound will also be different.

Stainless Steel = Thicker wall (heavy it will muffle some of the sound due to thicker wall)
Titanium = Thinner Wall (sounds louder than Stainless Steel) but way way lighter.

NOW THE BIG QUESTION WHICH OR WHAT WILL MAKE POWER?

thats a good question.... for our cars

NOW ITS TIME FOR YOU TO DO THE SEARCH...
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      08-02-2011, 12:48 PM   #5
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Here are some exhaust shots we took from the E9x M3 to show the setups.







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      08-02-2011, 05:20 PM   #6
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Quote:
Originally Posted by Sean05 View Post
im going to answer some the best way i can...

resonator = reduce the sound of the exhaust/muffler the more resonator the less annoying your car will be... also reduces rasp.

HFC = its less restriction compare to OEM meaning more air flow. less honeycomb. (smells)

Cat Delete = free flow. no air restriction more power (smells like shit)

200 cel or 400 cel = OEM cat has 400 cel HFC usually has 200 Get the idea? MORE FLOW, LESS FLOW

x pipe or Y pipe = the M3 has X pipe not a Y (cant really explain how this works) lazy on googling)

NOW the sound when you mix and match the resonator and cat it will sound loud depending on your exhaust.

with no cat and resonator your exhaust will be so FREAKIN LOUD. Now that being said adding HFC or resonator will reduce the rasp, and the sound of your exhaust.


EDIT:

Also when selecting exhaust pipe from stainless steel or titanium the exhaust sound will also be different.

Stainless Steel = Thicker wall (heavy it will muffle some of the sound due to thicker wall)
Titanium = Thinner Wall (sounds louder than Stainless Steel) but way way lighter.

NOW THE BIG QUESTION WHICH OR WHAT WILL MAKE POWER?

thats a good question.... for our cars

NOW ITS TIME FOR YOU TO DO THE SEARCH...
Thanks for the informative reply, I'll definitely be reading over this stuff in even more detail once I decide what exhaust/x-pipe to go with
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      08-02-2011, 05:22 PM   #7
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Quote:
Originally Posted by Nate@IND View Post
Here are some exhaust shots we took from the E9x M3 to show the setups.
Thanks for the wonderful pics Nate, makes it easier to understand visual wise. Is it necessary to get those connecting pipes when purchasing an Eisenmann muffler or even other companies such as Gintani and AA or would the following set-up work.. Eisenmann Race Muffler + OEM connecting pipes + challenge race x-pipe

Thanks
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      08-02-2011, 06:13 PM   #8
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Most exhausts include the connecting pipes. Eisenmann does not, so you need connecting pipes if you want a bolt on setup. Otherwise, you need to reuse your stock pipes which just adds to the difficulty.
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      08-03-2011, 01:16 AM   #9
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You're request for full detail and then the subsequent questions don't quite match up. I don't mean any offense. I'm just saying that there's a lot more to exhaust, more specifically combustion and scavenging than say cats, resonators, etc. More of your questions are pertaining to sound, versus optimal exhaust design for power and/or particular engine characteristics (e.g. wanting to achieve a flatter torque curve). The thing you have to keep in mind is that the exhaust, like the intake, is part of the entire engine assembly.

Keep in mind that the engine mapping is done with the stock exhaust in mind. If you go with a less restrictive set-up (i.e. eliminate all cats and even possibly the muffler), you would have to revise the engine mapping accordingly to get the maxium power benefit. Note that contrary to popular belief, some level of resistance in the exhaust stream is not desirable. Aside from proper header designs that are tuned (look up helmholtz resonance) to help scavenge exhaust from each cylinder (due to pulse waves emitted from valves on reciprocating cylinders, which would be 180 deg out of phase), any additional exhaust component is unecessary from a power standpoint. Also note that to tune an exhaust header using the helmholtz theory, implies that the exhaust would be tuned specifically for a given rpm, so a compromise in design (i.e. header length) is usually made to allow for gains in power of greater range of rpm, at the expense of generating slightly less power.

As an aside, the S65's intake is designed much the same way. The large intake chamber, aside from being designed for optimal flow, also takes advantage of having an enclosed area where pulse waves from reciprocating cylinders can be matched.

Going back to exhaust systems, take a look at the current F1 cars. They're actually blowing the exhaust on their diffusors to create more downforce. In this case, the aerodynamic gains outweigh any small drop in power by routing the exhaust to the diffusor.

With respect to material choices, consider the facts (aside from availability/cost). It has to withstand high temperatures, must have a low coefficient of thermal expansion, must be easily formable (bends, butted areas, etc.), etc.
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      08-03-2011, 02:27 AM   #10
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Like some of the the others have stated, there is a lot to exhaust systems. I went with the Akrapovic just because I liked the weight savings, the looks of the exhaust tips, and the over all build quality of the system...the extra power was nice too.

It can be very difficult to find the right exhaust for you, so I highly recommend doing lots of research because, quality exhaust systems for the M3's are not cheap.


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Originally Posted by piloto View Post
Going back to exhaust systems, take a look at the current F1 cars. They're actually blowing the exhaust on their diffusors to create more downforce. In this case, the aerodynamic gains outweigh any small drop in power by routing the exhaust to the diffusor.
Huh? Does that really work? I have no idea, but it seems like it wouldn't work...kind of like putting a big fan on a sailboat to blow wind into the sails. Then again, I'm by no means an expert on aerodynamics, and I would imagine the F1 guys know what they are doing.
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      08-03-2011, 07:45 PM   #11
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Quote:
Originally Posted by Rshane View Post
Huh? Does that really work? I have no idea, but it seems like it wouldn't work...kind of like putting a big fan on a sailboat to blow wind into the sails. Then again, I'm by no means an expert on aerodynamics, and I would imagine the F1 guys know what they are doing.

Abosultely. Look at what's been going on this season. In fact, Renault (now Lotus...the real one) has a front exiting exhaust specifically for this purpose, although it hasn't netted the gains they thought it would. RedBull on the other hand, along with Macca have really made it work. The crazy part is that they were losing downforce when off-throttle. So to compensate for that, they remapped the engines to retard the timing so that the charge can "escape" down the exhaust (essentially igniting in the exhaust, but not causing the engine speed to increase).Remember, the combustion pressure (or even the pressure of the unburned charge) and relatievly high rpm 18,000rpm make for some substantial fluid flow through the exhaust.

And your analogy isn't accurate. The blown diffuser isn't relying strictly on the exhaust flow. The exhaust flow is merely used to help create the necessary pressure differential to create the maximum amount of downforce possible given the formula's design limitations.

The same concept is used on some aircraft (known as the blown flap), where some pressure from the turbine is released over the flaps to create lift at low speeds.

It's not a new, nor an unproven concept.

Going back to exhaust and the OP, fluid dynamics is a complex subject matter that is not fully understood. For the sake of discussion, think how the shape (cross-sectional shape) of the tubing would affect the flow of exhaust gases. It can be quite complex, and at the same time it's rather insignificant because there are many other, more prominent factors (e.g. bends in the tube, material limitations, size limitations, noise suppresion needs, etc.).

So if you ingnore all of that and just want to buy one of the best, look for proper manufacturing techniques (mandrel bends, good quality welding, proper grade material), proper engineering to ensure it fits and functions as intended. No doubt the Eisenmanns, Akras, M Perf, etc. are a bit overpriced. They know people will pay, and have the right to charge high prices, and more power to them. But, you get a properly engineered part, that's made with the right materials, and the right manufacturing processes.
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