Muffler Removal - a Definitive Answer (finally!)

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Muffler Removal - a Definitive Answer (finally!)

Post by priapismic »

A few months ago a thread popped up about removing the stock muffler and a resulting increase in fuel mileage. While this subject has been debated many times over the years, and arguments pro and con are numerous (do a thread search on "muffler removal") I thought I would escalate the question to an independent and impartial source with knowledge of the subject. So I sent the follwing e-mail to Chris Sidah, the Tech Q&A editor for Rider magazine, and a well-known BMW wrench:

As a follow-up to your answer to "Ken" regarding rejetting and exhaust modifications (July 2008), and your detailed answer about valve overlap and back pressure: would the rejeting issue even exist on a fuel injected machine?

There is a fervent discussion going on at the BMW Roadster/Rockster internet forum (http://www.R1150R.net) regarding removal of the stock muffler, and running with just a chrome tip coming off the catalytic converter. Some on the board are of the opinion that the cat con has sufficient back pressure by itself, and that the factory muffler is superflous. And, in support of their argument that the muffler's removal will NOT result in a lean condition, they reason that the computer controlled ECU (which manages the fuel injection system) will compensate for any muffler removal and it's subsequent lean condition. Others on the board are just as adamant that muffler removal WILL result in a lean condition, generating excessive heat and insufficent back pressure.

What are your thoughts about fuel injection systems, cat cons, and muffler removal? A lot of people on the web are anxious to hear your verdict.


Here was Chris's initial brief reply to me:

The oxygen sensor plays the most important role in determining mixture. The cat, if I remember correctly, is a matrix type and would keep any pulse or pressure waves from the muffler affecting cylinder charge. Run the stubby pipe. I'll answer more in depth in the October issue.


Well, the October issue of Rider arrived today, and my letter was printed (see page 78 if you have the October issue). Here is Chris's detailed reply:

"I'm not sure that "verdict" is the right term, but I belong to the superflous muffler camp. I first saw the "JC Whitney Chrome Pipe Extension" modification at one of the Streetmasters sessions at Willow springs Raceway. The bike ran fine and had a very nice tone. BMW uses a closed-loop cat con and lambda sensor system to control mixture that is not dependant on exhaust system back pressure. The pressure waves that would help with cylinder charging are, by virtue of the cat con's placement, generated before the muffler gets in the act."


You guys can argue this all you want, but until you "experts" get your own advice column in a major national magazine, I'm inclined to believe that Chris is on the right path - muffler removal, and running with no can or a shorty tip (like my JC Whitney short tip) will NOT do harm to my engine. Therefore, I'm gonna keep running with my shorty tip. Besides, getting the stock muffler re-mounted is a major pain.
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Re: Muffler Removal - a Definitive Answer (finally!)

Post by Boxer »

Now that's why we call him "Priapismic". Like a magnificent wooden flagpole bearing the colors, standing tall in the face of a Texas tornado...Priapismic gets the answers!
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Re: Muffler Removal - a Definitive Answer (finally!)

Post by qfman »

I don't need no theories. I just did it. 80,000km with no muffler. Better top end. No dramas. Fact.

I am happy to be getting back my hearing back on my new(ish) R12R. It's got so much grunt you can leave the muffler on.

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Re: Muffler Removal - a Definitive Answer (finally!)

Post by rdsmith3 »

I've been running without muffler all summer my mileage is very slightly better.

However, I am still wondering if I need to put the CCP back in so that the O2 sensor can do its job?
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Re: Muffler Removal - a Definitive Answer (finally!)

Post by priapismic »

rdsmith3 wrote:However, I am still wondering if I need to put the CCP back in so that the O2 sensor can do its job?

Bob,
As I understand it, removing the CCP effectively changes the emissions control system from a closed-loop to an open-loop type. Therefore the cat con and O2 sensor is not doing quite the same job as before. In that case I'd say all bets are off - the cat con will not behave as Chris described above, and perhaps a muffler will be required.
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Re: Muffler Removal - a Definitive Answer (finally!)

Post by Photoguy »

I haven't followed the original discussion...how loud does the bike get without teh stock muffler?
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Re: Muffler Removal - a Definitive Answer (finally!)

Post by FloridaBeakster »

Photoguy wrote:I haven't followed the original discussion...how loud does the bike get without teh stock muffler?
Surprisingly, not that much louder than with it on (assuming the original catalytic converter is still there). It is a little bit louder and imparts a much nicer, throatier sound. It makes your bike sound like a motorcycle instead of a sewing machine. I would say that it is probably still quieter than a Y-pipe with an aftermarket exhaust.
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Re: Muffler Removal - a Definitive Answer (finally!)

Post by boxermania »

priapismic's post serves well the saga regarding removal of the muffler and potential damage to the engine via added heat, et. al.

From my perspective I feel that it is important to understand, in a simplistic way, what is taking place.

First and foremost, in the oilheads we have a very rudimentary FI and lambda system. The O2 sensor is of the "narrow" band, read one of the first versions, albeit heated. It also inexpensive, if you ever have to replace it (recommended at 60K miles as it becomes sluggish) buy the Bosch standard part and splice the wires to keep the BMW plug. ($40 to $60)

Second, close loop is a term coined from the EPA testing of emissions where the vehicles are tested under laboratory conditions and the emissions tests are run at idle and cruise, read, steady state conditions, obviously nothing reflecting real time operation of the vehicle. As such the effect of the O2 sensor can only be had under these conditions.....read, steady state operation. Under such the ECU with the signal from the O2 sensor will try to get as close as possible to the 14.7/1 A/F ratio and I say as close because you have to factor in the proper operation of the engine.

Remember the basics of internal combustion.....a leaner the mixture, within reason, will produce the best mileage, along with increased combustion chamber temperature and potential rough running, surging, as the result of reduced fuel energy.

This is where the mysterious CCP comes in. Most US bikes have been equipped with the ill fated yellow plug, however, it is a well known fact US fuels are inferior to the European blends. The purpose of the CCP is to have the O2 sensor operational during the idle and cruising phases. On the other hand a fair amount of US bikes have been prey of the feared "surging" at cruise speeds, i.e. small throttle openings, because the O2 sensor is trying to get the A/F ratio in the lean range to improve mileage. A very common practice, by some of the savvy BMW Tech's was to remove and discard the CCP when the owner came in and complained about surging and in most cases this eliminated the surging.

With the removal of the CCP plug, the engine sees what is referred to as the "open loop" fuel map during all phases of operation The open loop A/F map is tuned for a slightly richer mixture, at the expense of fuel consumption and in general the engine operates better and has a crispier response. (This is a very basic explanation)

So now, let’s go to the pressure waves in the exhaust in the presence of a slight back pressure (read pressure that is induced by the length of the exhaust and the diameter of the pipes/components) that have a positive effect in the filling of the cylinder during the intake portion of the 4 cycle as it creates a vacuum that improves the filling of the cylinder and hence more power.

With the advent of the cat, the muffler ceased to be the element with the greatest pressure drop as the cat took over this function. If you were to tap the exhaust to take pressure readings, just before the cat, between the cat and the muffler and compare it to atmospheric pressure you would see that the greatest pressure or restriction is between the exhaust valve and the entrance to the cat.

Also take note that the O2 sensor is at the entrance of the cat to measure the amount of unburned O2 in relation to the standard 21% that is present in the atmosphere. So any change in the A/F ratio is done based on what is seen at the intake of the cat, this is done to insure the longevity of the cat, because they do have a finite life as the catalyst is consumed

So let us review:

• The O2 sensor in the oilheads only controls the A/F ratio at idle and cruise (inexpensive and slow response)
• For the O2 sensor to operate the yellow CCP (US bikes) will have to be in place
• BMW Techs have been known to remove the CCP (quietly) to assist with customer surging complaints
• The A/F map without the CCP is a bit richer in the idle/cruise conditions
• The cat converter is the major back pressure component in the exhaust and being placed ahead of the muffler it reduces the muffler contribution significantly.
• There is no damage that can become the engine via heat or otherwise by removal of the muffler....we identify with mufflers and expect a muffler. Besides what better way to remove 10+ pounds from the bike and look at that open wheel.

The mileage issue increase or decrease is very debatable and with everything equal, state of tune, operation and combustible, if there is a +/- change it should be very, very slight. With the CCP off there should be a slight mileage loss, everything else the same.
Last edited by boxermania on Thu Sep 11, 2008 7:59 am, edited 3 times in total.
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Re: Muffler Removal - a Definitive Answer (finally!)

Post by priapismic »

Splendid explanation, Al!

Thanks, and well done!
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Re: Muffler Removal - a Definitive Answer (finally!)

Post by beemerboy »

Im still scared for sure to take it off, but you guys seem like the research has been done.
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Re: 94 decibels

Post by qfman »

I actually had to have mine properly tested and certified for the pleasure of running without the muffler. It blew 94db at 3500 rpm. I think it is arount 83db standard but the difference from 83 to 94 isn't 12% - it's more like 40%. Sound in dbs increases on a slightly exponential scale.

Tried it on the R12R and it is waaaay too loud.

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Re: Muffler Removal - Detrimental Exhaust Heat?

Post by Coffeebean »

I recently removed my muffler and have been riding for about 500+ miles so far without it. I love the open sound and difference in the bike. I have been wondering lately if the exhaust heat affects my rear tire and wheel... I touched the tire earlier today after about 100 miles on some backroads and found it to be incredibly hot! I then touched the front tire and did not have the same heat transfer...Is it the final drive transferring all of that heat or is my exhaust playing a role in this? Should I worry about a chance that my tire could explode???

opinions??
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Re: Muffler Removal - a Definitive Answer (finally!)

Post by riceburner »

priapismic wrote:
rdsmith3 wrote:However, I am still wondering if I need to put the CCP back in so that the O2 sensor can do its job?

Bob,
As I understand it, removing the CCP effectively changes the emissions control system from a closed-loop to an open-loop type. Therefore the cat con and O2 sensor is not doing quite the same job as before. In that case I'd say all bets are off - the cat con will not behave as Chris described above, and perhaps a muffler will be required.

The way I understand it works is that the Motronic has a set default "injection map" and uses the O2 sensor etc in conjunction with this map to control the fuel injection.

Adding one of the various different CCPs to the socket alters the injection map.

Ie the system still uses the O2 sensor etc with or without the CCP, but it serves the bike with differing amounts of fuel, depending on what CCP is plugged in. IE it's "closed loop" whatever. It would only be "open loop" if you removed the O2 sensor completely.
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Re: Muffler Removal - Detrimental Exhaust Heat?

Post by Ves »

Coffeebean wrote:I recently removed my muffler and have been riding for about 500+ miles so far without it. I love the open sound and difference in the bike. I have been wondering lately if the exhaust heat affects my rear tire and wheel... I touched the tire earlier today after about 100 miles on some backroads and found it to be incredibly hot! I then touched the front tire and did not have the same heat transfer...Is it the final drive transferring all of that heat or is my exhaust playing a role in this? Should I worry about a chance that my tire could explode???

opinions??
Tires get hot when they get used, especially if you're doing back roads with lots of curves. The front tire will get hot too if you're doing a lot of heavy braking and turning. I would check the cold tire pressure to make sure you're pressure is good and you're not overheating the tire because of low pressure.

I don't see how the exhaust could significantly increase the tire temperature, unless you intentionally routed it to point right at the rubber... which of course you didn't.
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Re: Muffler Removal - a Definitive Answer (finally!)

Post by Coffeebean »

I don't see how the exhaust could significantly increase the tire temperature, unless you intentionally routed it to point right at the rubber... which of course you didn't.
no, i didn't...i was just curious after my observation yesterday....
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Re: 94 decibels

Post by harrisphil »

qfman wrote:I actually had to have mine properly tested and certified for the pleasure of running without the muffler. It blew 94db at 3500 rpm. I think it is arount 83db standard but the difference from 83 to 94 isn't 12% - it's more like 40%. Sound in dbs increases on a slightly exponential scale.

Tried it on the R12R and it is waaaay too loud.

Tom
Tom you are right Db is a logrithmic scale
a 3 db increase is a doubling of of sound
for example 2 BMWs running at the same speed with the same system would register 3 Db more than one bike on its own
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Re: Muffler Removal - a Definitive Answer (finally!)

Post by ASQTec »

I must say that I am a bit disappointed.

The title of this thread stated "a Definitive Answer." Here I am thinking that this will be the last post ever on this forum about mufflerectomies. I could not find a "definitive answer," so I now feel compelled to add my dos centavos.

I believe you can say many things about our boxer twins, good and bad, but there is nothing you can do to make them sound good. You can put lipstick on a pig........

I took my muffler off last winter while giving my bike a thorough cleaning, and then went for a ride. I became very insecure when I couldn't hear my timing chain tensioner rattle...I felt as if I lost an old friend. I can tell you how fast I'm going just by knowing which gear I'm in, and when the rattle kicks in.

Besides, the charcoal canister really throws off the visual balance of the bike with the muffler removed.
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Re: Muffler Removal - a Definitive Answer (finally!)

Post by priapismic »

Well Anthony, the "definitive answer" had nothing to do with the sound. That is highly subjective, either you're gonna like the sound without the muffler, or you won't. Some people think the lipstick makes the pig look better :smt057 and some surely don't :smt078

Anyway, my OP wasn't about the sound, it was about running lean and damaging your engine *if* the muffler was removed. I don't think that argument holds water any longer ...
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Re: Muffler Removal - a Definitive Answer (finally!)

Post by paddle007 »

Hi guys,
New to this site and my first bike in 30 years, a 04 R1150R. This thread caught my attention. I may be sticking my neck out with the closed loop/open loop theory but here goes. I am an auto tech with thirty five years experience and my understanding is open loop is when the oxygen sensor is too cold to generate voltage. They only work when they are hot, even an extended idle will bring it to a non-operational state. Automotive closed loop is typically :-k a normal operating temp. and heated oxygen sensor. ODII cars, 1996 and newer heat up oxygen sensors to keep them active. Seems like removing the O2 sensor on our Beemer is taking away some of the logic of the PCM. In open loop not all of the inputs are used, hence a richer/dirtier exhaust. Out of curiosity does the oilhead use a map or maf sensor? Got alot to learn about this bike. Input greatly appreciated.
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Re: Muffler Removal - a Definitive Answer (finally!)

Post by jnannini »

Can anyone answer if the o2 sensor still working even if you remove the CPP?
For me have sense what I read that the motonic uses the euro map when you remove the CPP and the only way to have the system working in a open loop mode is removing the o2 sensor.
I have a 2004 R1150R Rockster with K&N air filter and Y-pipe with stock can, the bike run fine when is cold, no surging, no popping nor backfire, but when the bike gets hot is terrible, very bad engine noise, popping, shake, etc...
The bike came with no CPP plug since new
If the 02 still working, I will try the techlusion 259
Please help...real answers... no especulations.....
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