Muffler off; Mileage up

[Dr. Strangelove]

OK, I don't know if this is crazy, or serendipitous, or real.....

I removed the muffler and put on the extension a la DJDownunder.

Like the new sound a lot and it is maybe a little peppier, though that could be my imagination.

What is not my imagination is the mileage increase I am seeing.
Prior to removal I was getting 38-42 with my regular riding. Rarely on a tour I would get north of 5o, but that, as stated, was very rare and only happened a couple of times.

Now, sans can, I am regularly getting 46-47 mpg with my regular riding. Yesterday I filled and got 49.995 mpg and that included an 80 mile run at about 80-85 mph. 205 miles on the odometer and she took 4.1 gallons (@ 3.999). The fuel light isn't going un until north of 170 mi. I am not trying to save fuel with my riding style.

Thoughts? Can removal of the muffler result in a 17% improvement in mileage? BTW I am using 89 octane.

John

[towerworker]

Might be worth a shot for me. I can pretty consistently get 50 providing I'm easy on the throttle. I have gotten as much as 54 but that was running the BRP here in Va at a pretty steady 45-50mph.

What I would really like to get shed of is the cat. Alot of weight and heat under the engine. I like the looks of the can and I especially like the lack of noise.

[Dr. Strangelove]

The noise increase is not that much if at all. It is a change in the characteristics of the sound--more throaty, deeper, fuller.

But the mileage change by itself is worth the price of admission, if it is related???

[boxermania]

John

The greatest restriction is in the cat, the muffler does add some restriction, but not much. Personally I can believe 1 or 2 miles increase in economy everything else being equal, but 5 or 6 miles more.....well that is plainly too much.

However, being that has been your experience all I can say is more power to you....in addition you removed about 9 lbs off the bike as well....Kudos.

[Boxer]

That IS odd. Some of us have gotten LESS mileage with it off. One of the reasons I put mine back on was the mileage decrease and the continuous sound bugged me on the open road....Err, make that 2 reasons. I can't do high math.

[Dr. Strangelove]

I'll keep y'all posted, but this has been over a number of tankfulls, and some spirited riding.

I am beginning to get comfortable with the low fuel light not coming on until 170 miles.

I have a problem believing it also and that is why I asked if it was serendipitous.

[zeke]

Sounds good to me!!! I am kinda new to the R and have been trying to improve my fuel economy. I'll help you test your theory...maybe the results will replicate. Ah....is there any secret method to remove can/silencer? Is is basically remove the nut that secures it to the frame, twist and it pops off? Is there a post I can reference for assistance?

[R4R&R]

Could it be different mixes of fuel that changed your mileage? The 10% ethanol we have in all flavors of our gas seems to decrease the mileage.

OTOH, I like the bike making a little more noise while not being obnoxious. Fitting a full sized left case is a great bonus!

[beemerboy]

so i pulled my muffler off as i had previously stated in a different forum and everyone on there kinda slammed me and said i was gonna hurt the engine because it would run to hot. I also got the same answer from BMW dealer so i put it back on. I would really like a straight answer if someone could help.

thanks
chris

[Beemeridian]

13

[big papa]

I ran my Rockster for 2 years sans can...

[priapismic]

Curious .... I can understand a modest increase in fuel economy, but your seems excessive. Still, the numbers don't lie, so if that's what your experiencing, consider it a gift and take it!

I'm on my third iteration of using a shorty tip in lieu of the stock muffler. First time I removed the can was a couple of years ago, I ran with the shorty tip from J.C. Whitney for a couple of months. I even added the tiny "muffler" insert into the short tip (not that there was any difference). I eventually put the stock muffler back on because I felt like my fuel mileage went down, plus I thought I detected a slight hesitation at full throttle, like when I wound it up to pass.

About a year ago I decided I would experiment again and removed the muffler for a shorty tip. This time I left the shorty tip on for almost a year, and kept mileage records. Here are some MPG numbers from a June 2007 trip, again with the shorty tip in place of the stock muffler:

43.3
40.8
41.88
41.13
41.8
42.09
40.70
42.3

Here are some numbers from my November, 2007 trip to Arkansas for the min-Bash, again using the shorty tip:

42.5
45.75
40.03
43.5
43.38
39.8

Overall aggregate average mpg using the short tip: 42.06

A few months ago, as the price of gas was starting to shoot through the roof, I decided I would experiment again by placing the stock muffler back on. I ran with it that way for a couple of months. Here are some trip numbers:

40.8
45.6
41.92
42.3
43.6
44.9
48.4
44.47
41.0
44.23
42.45
42.0

Overall aggregate average mpg with the stock muffler: 43.47

Not much of a difference, eh? I guess if you want to run with a full-size left system case, or if you insist that losing the weight of the stock can will help you somehow, go with a short tip on the cat and lose the muffler. If you're worried about doing damage to your engine by running without it - and I'm not convinced of that, one way or another, and won't be until I see an exhaust gas analyzer report on my bike fitted with the shorty tip - then go ahead and be safe and keep the stock can on. It's been posted in other threads that your engine and exhaust system have been factory engineered and tuned to work together; I don't dispute that, but remember that the factory has other goals in mind when they are developing exhaust systems and engine management software for the ECU - namely, emissions control (particularly in Europe, where the regs are quite stringent), and also noise control. So, is the factory system "best"? Not necessarily for mileage or performance.

As for me, I will again remove the shorty tip and replace it with the stock muffler one day soon. Though I love the visceral growl of the short tip, and the reduced weight, that little bit of additional MPG just might come in handy in times of $4 and $5 per gallon gas. Problem is, fitting the stock can back on is a freakin' Bear, I can't quite get a good fit, and the muffler ends up loose and rattling. I need a cool day and lots of patience to want to fiddle with it again.

[johnnyjs1]

How on earth are you gettin 170 miles before the light turns on? My light consistantly comes on between 120-130 miles. My bike has 11k on it now, will the mpg go up as the miles get higher? I have a Rockster, that shouldnt make a difference should it?

[Dr. Strangelove]

Man, I tell ya, that's what's happening. Today, the yellow light did not go on on the side stand until 150, and then promptly went out when upright and underway.

I am buying gas at the same places, though they may have switched to the summer grades, but no increase has happened before.

Re removing the can: 2 bolte--a 6mm hex on the sub frame--is that what it is called? the black triangular piece that the rear peg attaches on to. And a 15mm SOB of a bolt to remove at the cat converter--get underneath and you will see it. Then it is a twisting motion.

John

[Beemeridian]

11

[zeke]

Beemeridian....I don't want to get to far off the topic of the post, but you bring up another point. Can I take off that charcoal filter as well? Will removing it help improve my MPGs? How do I take if off? Figure if I am taking off things off might as well do it all at once.

[beemerboy]

haha so taking off my muffler should not hurt the bike?

the bmw dealer said its gonna make it run lean and hot

[Dr. Strangelove]

Could be a combination of how high you fill the tank with a heavy throttle hand. I have a light throttle hand, do mostly country road cruising, and fill the tank with the extra 3/10ths available beyond the bottom of the filler neck (IF I will not be parking for 20 miles, because the charcoal canister is off), and I average 47-48 indicated MPG, which translates to about 44 real world MPG. The fuel light comes on around 180.

I am filling the tank to auto shut off at the same pumps I always use. I do not overfill. I do not have a light hand on the throttle. I do a lot of steady speed at 73-74 indicated--69 on the zumo.
My commute is about 75 miles. 15 of it is stop and go city, never into 6th. This has been what I have always done.


Could it be that the resistance to "flow" imposed by the muffler had that much of a negative effect on my mileage? Could the valve adj and TBS be so spot on that with the removal of the can I am seeing an ideal situation (formerly "muffled" by the muffler)?

I am probably seeing the same readings as you are, Dave.

the bmw dealer said its gonna make it run lean and hot

Prior to removing the muffler, I did notice on occasion that the exhaust smelled a little rich, I do not notice that nearly as much now, so it may be leaner.

Re the hot: I do not feel any more heat coming from the engine--totally unscientific I know, but I have been sensitive to it. But even if the engine IS running a bit hotter, if I am saving money on gas then maybe it is a risk worth taking--all very Zen- a balance worth adjusting.

John

[rdsmith3]

Dr. Strangelove,

Do you have your Cat Code Plug (CCP) in or out?

If I can get a little more mpg, I may take that muffler off again.

I am running without the CCP, and have been doing that for years.

[NoRRmad]

Just a theory.

You want more milage? Restrict the air intake. The best milage I ever got on my Roadster was loping along the high plateau in Wyoming, with altitudes above 8000 feet most of the way. (Fifty-seven MPG and change.) Duplicating high altitude in the airbox just requires restricting the intake -- maybe with an extra concentric air filter, or just some duct-tape across the snorkle. The computer will lean the mixture to correspond with the apparent altitude and power will drop, as will fuel consumption.