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Discussion Starter #1 (Edited)
Gi Guys,
Here is some information with respect to the BMW exhaust, air flow, back pressure and it's design which was written by Steve Dinan. After reading this, I concluded that our car's resonator "more than likely" hurts the car when it comes down to horse power and overall performance. Here is S.D's information on this subject. What's your take on this matter? Based on his research, we should ditch our car's resonator, right ???
Thanks for your replies and sharing your opinion.

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Exhaust Theory
There are two major areas of the complete exhaust system that are typically tuned for enhanced performance; the exhaust manifold .or header and the rear muffler(s). The exhaust manifold’s length, tubing diameter and the manner in which each cylinder is linked to the other is critical when attempting to maximize an engine’s power output. The manifold configuration can be manipulated in order to generate maximum power at low, middle or high rpm, changing the shape of the power curve accordingly. Naturally some compromise must be accepted when tuning an exhaust manifold for a street-car as the goal is typically to ensure balanced power output at low, middle and high rpm. This is in contrast to a race-engine where the exhaust manifold can be tuned specifically for maximum performance at high rpm.

After the exhaust manifold or header, optimum performance comes from making the balance of the exhaust system as short and large as possible. This approach will result in greater engine efficiency for maximum power, as well as minimizing the weight of the system. Probably the best example of an optimized, no-compromise exhaust system would be that of an F1 racecar. If you have ever had the opportunity to hear an F1 exhaust note, I think you will agree that it is best described as deafening. Clearly an exhaust system that even approached such a volume level in a performance street-car would draw far too much of the wrong sort of attention. Therefore, a modern street-car exhaust represents a number of performance compromises in order to achieve an acceptable exhaust volume, as well as meeting emissions standards.

In order to accommodate the various components and baffling necessary for a street-car, the exhaust system becomes longer and the flow of gasses more circuitous as noise and emissions standards are addressed. Each bend in the exhaust tubing, catalytic converter, resonator and so forth introduces restrictions to the exhaust flow, particularly at higher rpm where flow is most critical. Exhaust flow can actually reach hundreds of miles per hour when the engine is producing maximum power, which results in power robbing friction along the exhaust tubing
walls, particularly when the gasses must change direction. This friction results in increased backpressure that can be quantified with a pressure gauge. In addition to the friction issue, a tube or opening that is too small will result in extra backpressure as well. This backpressure restricts the amount of gasses that can be passed through the engine, resulting in a reduction of peak power.

I’m fairly certain that many of you have been exposed to a “bench racing legend” that would have you believe that increased backpressure will improve low rpm power and that low backpressure will increase high rpm output. Nothing could be further from the truth. An exhaust system is sized for maximum flow at wide-open-throttle and peak rpm. All exhaust systems are “oversized” for lower engine speeds (rpm), as backpressure is so insignificant that it can’t even be measured. Less back-pressure always results in more power at higher rpm, with no negative effect on lower engine speed performance. The amount of power that can be extracted from an
engine at a given rpm as a result of exhaust design is really limited by the exhaust manifold or header. After the header, less backpressure is always better.

The real challenge when tuning a street-car exhaust is to increase flow without making the system so loud as it becomes unacceptable or even illegal. It is also important to understand that vehicle manufacturers must meet more stringent maximum volume requirements than aftermarket manufacturers.

BMW’s current M-cars feature a distinctive quad exhaust tip design, punctuating the cars’ high performance image. This approach is very logical when applied to a “V” engine configuration because there are natural dual exhaust outputs with this engine design. >>> END.
-------------------------------------------------------------------------- :cheers:
 

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yeah, steve did this lecture back at an open house several years ago. Not sure why they keep the m5's resonators, other than sound control/quality. I think many people have demonstrated a few hp gain with the SS X pipe.
 

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there are always compromises in automobile design and as such we know for a fact that the m5's resonators as well as all other models of bmw's resonators are a sticking point for power as well as sound output.

The issue that we as ///M owners must realise is that BMW M did a pretty **** good job of doing the exhaust to a subdued tone while maxamizing power output.

Honestly, i wonder how much power i would have gained with the biggest cats, headers, xpipe and loudest muffler (we all know what kind it is) vs a stock car. The headers as has been proven, open up the kink in the exhaust setup but the rest of the tract provides little power increase.

Sure the resonators are maybe a little restrictive but I honestly believe that bmw put them in there more for sound rather than power. Remember there are only a small faction of us M5 owners that post on here and even fewer that actually remove the resonators when combined with an exhaust (there are those freaks that remove the resonators with the stock cans---MAH).

its all about keeping the fairly luxury laden feel of the car without it turning into a z06 interior with the resonance and decibel level that some of us deal with.
 

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I have Magnaflow on mine.
Not much louder then stock when ******* on, the larger tube dia. had to help with the Hp/Tq numbers.
Plus the 30# of steel you loose is a big help.
 

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Hey Robert and Rob,

Don't forget Weight.

That big Horse-shoe weighs a Motsa.

The Tubi is a far sweeter melody. It has the eye candy resonators that keep the noise under control, and look great at considerably less weight.

I think this is maybe why Tubi has the highest power claim for exhaust (6 HP), becasue of the resonator removal, and replacement.

Didn't Steve Dinan also tell Germansedanfans (Paul S) That he lost Power on his S2 becasue of the "X-Pipe?

And whne he put the Resonator back on with the Dinan can most of the Power was restored?
 

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SC'dKellenersM5 said:
there are always compromises in automobile design and as such we know for a fact that the m5's resonators as well as all other models of bmw's resonators are a sticking point for power as well as sound output.

The issue that we as ///M owners must realise is that BMW M did a pretty **** good job of doing the exhaust to a subdued tone while maxamizing power output.

Honestly, i wonder how much power i would have gained with the biggest cats, headers, xpipe and loudest muffler (we all know what kind it is) vs a stock car. The headers as has been proven, open up the kink in the exhaust setup but the rest of the tract provides little power increase.

Sure the resonators are maybe a little restrictive but I honestly believe that bmw put them in there more for sound rather than power. Remember there are only a small faction of us M5 owners that post on here and even fewer that actually remove the resonators when combined with an exhaust (there are those freaks that remove the resonators with the stock cans---MAH).

its all about keeping the fairly luxury laden feel of the car without it turning into a z06 interior with the resonance and decibel level that some of us deal with.
Yes I admit that I had the SS x-pipe with the OEM cans as my 1st exhaust mod. for about a year, but it did make a difference in weight and response. It was slightly louder with a little raspy noise on deacceleration, but a good inexpensive mod none the less.

Of course I them moved on to the Tubi a couple of years ago and have been even happier ever since. The Tubi incorporates its own resonators, x-pipe and mufflers into a very light package that has just the right exotic sound for me. The sound by the way has grown with time to be a bit louder on acceleration. This probably is the case with any exhaust though.

Mark
 

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Guys,

im totally with you on the weight savings but i was speaking specifically about exhaust flow and such as that is mainly what the article Robert provided spoke about. We all know that the stock resonators are heavy...
 

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I do remember reading that, but i don't fully buy it. If it happened, it was likely because dinan's software is setup for the restriction from the resonator. If one were to get the car tuned for less backpressure, it should produce more power.
At the time, it was probably like going to the dealer with a fault code after you've done some mods, it's always the deviation from how the factory wants it that causes the problem (in this case, dinan being the factory).
Mike

MIB said:
Didn't Steve Dinan also tell Germansedanfans (Paul S) That he lost Power on his S2 becasue of the "X-Pipe?

And whne he put the Resonator back on with the Dinan can most of the Power was restored?
 
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