The CAT again

[JamesW]

Here we go again. I wasn't going to post my findings after cat removal last week but after a couple of test rides I can't resist. I really didn't think that I would see any actual performance improvements but I was wrong and Tracy Prier was right. Power delivery at low RPMs was greatly improved. Low speed 5th gear throttle roll-ons were un-believable. The machine sounds like a Porche 911 when you turn up the wick as in passing other vehicles. Even the neighbor noticed the throatier sounding exhaust note not necessarily louder just throaty, nice! Cold starting seems easier and idle is smoother. There is no observed back-firing into the muffler. I have not removed the code plug as there really is no reason to do so. Now, I agree that the cat does not restrict exhaust flow but I believe it creates a standing wave affect between the head pipe and the cat chamber and I believe that there is most likely not an across the power band increase in power output but rather a re-distribution of torque from higher RPM to lower and mid-range engine revs. Of course I have no way to actually prove this theory other than my observations during several test rides. Was it worth $55 to perform this modification?

 

Sorry Shovelstroke.

[Art..]

Show us the money. Put that sucker on the dyno

[smiller]

Yeah, sounding like a Porsche 911 is worth at least 20 psych horsepower.

 

Seriously, I'm not saying that the gain is necessarily imagined... but I do agree that some kind of objective test is necessary to confirm.

[JamesW]

Wellll, I'm afraid the only subjective test I am likely to perform is the one that originates right from the seat of me pantaloons. That is the only cost affective test I can justify in my mind considering the relatively small capital investment. I did give some thought to the phsycological theory and it didn't wash. Take it or leave it.

[Al Navecky Jr]

Where did you get the pipe to replace the CAT

[JamesW]

No pipe needed as the cat chamber was simply cut open and the cat element was then surgically removed then the chamber was welded closed and the complete muffler package re-installed on bike. Looks completely stock. I also must say that the throatie exhaust note alone was worth the catectomy. Always did have a thing for the Porsche 911:)

[russell_bynum]

Wellll, I'm afraid the only subjective test I am likely to perform is the one that originates right from the seat of me pantaloons. That is the only cost affective test I can justify in my mind considering the relatively small capital investment. I did give some thought to the phsycological theory and it didn't wash. Take it or leave it.

 

I heard of one study where they replaced the throttle return spring with a heavier one...and people reported performance gains.

 

Reports from the butt-dyno are worthless.

[LJR]

Simple 1/4 mile run on your local backroad will tell the story. Would have been nice to get a "before".

 

Top speed is a good indicator of horsepower.

[steve.foote]

What Larry and Russell said.

[TracyPrier]

First off. Thanks James.

 

I have to say I was pretty offended by Ed's comments about me making results up so that they fit my expectations... then I suppose some folk just can't handle people disagreeing with them.

 

Essentially he called me a liar which I don't take kindly to I must say.

 

I had no real expectations when I did my CATectomy, it cost so little it and was done in the vein of, "if there's no difference then no big deal it only cost $20 and some time".

 

I placed my findings on my web site with the idea that, like similar sites the info might be of interest or use to someone else. If you don't agree with my findings then fine, but don't go accusing someone you've never even met of lying... that's not very gentlemanly. And unless you've done the same thing yourself HOW THE HELL WOULD YOU KNOW IF IT WAS RIGHT OR NOT?

 

And to the guys saying if it ain't dyno'd then it's not worth anything... hey you're entitled to your opinion of course but I would say this;

 

I never set out to build up some incontravertable, government-guaranteed scientific study of the thing, I just did it and posted up what I had noticed and found.

 

I personally don't care whether there is more actual horsepower, I'm happy with a smoother bike that gets better fuel economy.

 

James, I'd be interested to know what your fuel economy does after this??

 

Tracy

[steve.foote]

Tracy, let's go through this again.

 

#1. No one is calling anyone a liar or questioning their integrity.

 

#2. It is perfectly normal for claims of any benefit to be scrutinized for accuracy.

 

#3. Demonstrable benefits can be, well, demonstrated.

 

The reason claims of additional performance, economy, speed, horsepower, comfort, etc., are questioned in forums like this is because so many of the claims turn out to be incorrect. What one rider perceives as an improvement may not be perceivable by another. And, if no measurements are recorded before and after against stationary benchmarks, the entire matter becomes nothing more than perception.

 

Hang around this board long enough (any forum for that matter) and you will see claims of all sorts being professed. The only ones which will hold up to scrutiny are the ones which can be legitimately documented against such benchmarks.

 

And, as for Ed, he can speak for himself, but one thing about him is certain. He knows quite a bit about this stuff and you can count on him being straight up about it. You won't have to wonder if he's just trying to be nice to you so your feeling don't get hurt.

[chrisstroh]

I believe Tracy and James at their "percieved" findings. It's gotten my curiousity up enough that I'm going to gut my cat the first chance I get. They sound sincere and credible. And I appreciate them telling us their findings and that nice website that shows step by step of how to do it.

http://www.myr1100rtp.netfirms.com/catelement.htm

He's not making any money out of it and went to a lot of trouble to document the procedure. I suppose a dyno might show different but then it might not. Now I guess the next step would be to ask the next Rt owner that's considering doing this to get a before and after dyno test.

Oh, was it proven that the cat doen't have much back pressure because looking the the pics of the resonator it looked restrictive?

Chris

[russell_bynum]

I believe Tracy and James at their "percieved" findings. It's gotten my curiousity up enough that I'm going to gut my cat the first chance I get. They sound sincere and credible.

 

Sincere...sure. But how can you be credible without data?

 

And I appreciate them telling us their findings and that nice website that shows step by step of how to do it.

http://www.myr1100rtp.netfirms.com/catelement.htm

He's not making any money out of it and went to a lot of trouble to document the procedure.

 

Yes, the website was quite well done.

 

But let me offer my experience. When we bought Lisa's RS, we bought a Remus exhaust system for it The ONLY reason we did that was because Lisa liked the sound of the Remus better than the stock pipe and she felt that getting the sound she wanted was worth the money.

 

I noticed absolutely ZERO performance change after installing the Remus. We didn't get better mpg, the bike didn't start any easier, and I seriously doubt it made more power...though it does SOUND like it's making more power. Again, this was a full Remus exhaust with the large resonator chamber, no catalytic converter, and a remus can. There's a removable baffle in the can, and I don't notice any difference with it in or out...other than noise.

 

So...I'm not being skeptical just because I enjoy it. I'm being skeptical because their claims don't make sense, are not backed up with data, and do not mirror my own experience.

 

 

I suppose a dyno might show different but then it might not.

 

?? If the motor is putting more power to the rear wheel...or even if it is putting the same peak power to the rear wheel, but the shape of the power curve has changed, that will show up on a dyno.

 

Maybe I should ask this a different way...how would performance change without a dyno being able to detect it?

 

Now I guess the next step would be to ask the next Rt owner that's considering doing this to get a before and after dyno test.

 

Uhh...based on your earlier statement...that's you. Please let us know what you find.

 

Oh, was it proven that the cat doen't have much back pressure because looking the the pics of the resonator it looked restrictive?

Chris

 

Nothing was proven because no before/after data was recorded.

[chrisstroh]

Sincere...sure. But how can you be credible without data?

...........................................................

 

Humans aren't machines. Anybody can look at a stats sheet, but I'd rather hear it from a person's personal perception. I trust that more. If it's percieved or not the bottom line is that they had a pleasant surprise and they both found their bikes running better and sounding better. When I asked about whether throttlemiester was the best device to use I got many people's experiences (all different)and I have to make a judgement based on that.

It sounds intriging to me too. Isn't that what most bikers want-to increase their riding pleasure? My question should have been does removing the cat give you a percieved increase in HP? My mistake. If 2 sincere people say it does then I might want that pleasure too. At this point maybe increased HP was not what I was looking for. Maybe a more pleasurable riding experience? Can you get that from a dyno?

For $50. I'll take a chance on what these guys "experienced". I appreciate you trying to save me the time and money to.

If and when I do this (I have 2 kids who come first)I'd still want to dyno it just out of curiosity. (a human emotion)

How much is a dyno test anyway?

[ShovelStrokeEd]

OK, Let's clarify a couple of things.

 

First, I did not call Tracey a liar. I did say his preceptions are proabably wrong and his "science" left some room for doubt. My reasons for saying so had nothing to do with people disagreeing with me, they do so often and I have a pretty thick skin. My reasons were based on experience with the same thing.

 

Back in '94, I worked, in a consulting mode, with Luftmeister and RB Racing on development of some parts for the then new R259 motored bikes (oilheads). Luftmeister, for those of you with long memories, had a very nice business dealing with BMW performance parts. RB Racing was building the exhaust systems for the BMW turbo kits for K and R (airhead) bikes. When the oil heads came out, it was natural that they wished to develop parts for those bikes. I was on hand and had a '94 R1100 RS that we could use as a test mule. Tools available for development were a hydraulic pump type rear wheel dyno, Bob Behn's expertise in re programming chips, Bob owns RB Racing and knows EFI inside out. He builds his own systems from ECU's up. We also used butt dyno, also known as the 91 freeway, and two trips to Palmdale drag strip. In addition, we had Matt's, the owner of Luftmeisters, stock '94 RS to use for side by side comparisons.

 

First off we ran base line runs on both the bikes at the dyno and the drag strip. BMW clutches being what they are, we did not really attempt hard launches but were after consistancy in launch to make data more meaningful. 1/4 mile speed is a very good indicator of HP and the launch is more important for ET than it is for finishing speed. FWIW, I have been drag racing motorcycles since the 60's and have a pretty good idea how to get a bike out of the hole quickly. The side by side thing was somewhat more subjective as Matt weighed about 160 lbs and I was in the mid 230's at that point.

 

Now to some hard data. At least as hard as 12 years and a 63 year old memory can provide.

 

Stock, both bikes provided about 79 RWHP and 65 lb/ft of torque at their peaks. If these numbers seem low it is due to the type of dyno used. Later dyno runs were made on a couple of inertia type dynos and did indicate about 10% higher numbers. At the drag strip, both bikes, with me riding them, produced ET's in the mid 12's and right in the 106 mph range. Informal top speed runs on the butt dyno showed Matt's bike to be a little faster at 143 indicated, mine at 139 although aerodynamics were probably at play as I'm a good deal wider and couldn't tuck in as well due to a readily visible protrusion in my waist region. He was pulling away a bit though.

 

Back to the shop where we fabricated a cat eliminator pipe onto which we hung a can from an old Kerker to keep the noise down. Didn't really do much in that mode as those old Kerker's were pretty darn loud. Our's came off a 1000cc Kawasaki as I recall. It certainly was in no way restrictive as you could practically see the exhaust valves through the can. The "baffle" was no more than a straight tube with some louvers punched in it.

 

Back to the dyno, hmmmm, 78 RWHP and 65 lb/ft of torque with a bunch of holes and dips in the formerly smooth torque curve. We had some work to do. Given normal atmospheric devieations, for which we were not correcting the numbers, the elimiation of the cat and stock muffler did, at best, nothing very much. "Had to be the fuel curve" we decided, and off to the EPROM burner we went. Weeks of testing and quite a few trips up and down our butt dyno later, not to mention about 20 dyno runs, we got the curve optimized for that system with the best dyno results coming on one great 60 degree night where the bike broke 83 RWHP and 71 lb/ft of torque. On that same night, it also topped the 140 mark with me riding out on the macadam dyno. The bike did feel crisper and would no carry the wheel in first gear a little ways instead of just popping it up a bit.

Hit the drag strip that weekend and Matt's bike, which was still stock, ran the same mid 12's at 106 mph while mine would get down in the 12.3 range and was at around 108 mph with one run, late in the day when it had cooled off a bit and I was particularly agressive about the launch, just barely at 110 mph. Attributed mostly to it cooling off and a bit of wheel spin on the launch which helps mph.

 

So, in conclusion, at last you might say, there might be some small benefit to removing the cat and stock muffler if you compensate for changes to the exhaust system by changing the fuel curve to suit. Just removing the cat without going the extra step will gain little or nothing unless steps are taken to change the fuel curve.

 

Finally, as to the resonance thing, the primary resonance pulse, and the strongest, will take place at the transition between the head pipes and the collector and is a function of head pipe length. It is the diameter change which generates that pulse. It may be that removal of the cat element would generate a secondary pulse as the collector pipe will now see another diameter transition but the pulse will be a good deal weaker. These pulses typically work over a pretty narrow range of RPM and mostly are ineffictive at part throttle operation anyway.

 

That's my story and I'm sticking to it.

[Ken H.]

I heard of one study where they replaced the throttle return spring with a heavier one...and people reported performance gains.

Yeah, I remember that one, hilarious! And a world of truth spoken!

[Ken H.]

Interesting outcome.

 

Not directly related, but maybe someone can help...

 

Of late I've been noticing some performance variations in our 12GS that I'm trying to sort out. When I ride to work in the morning with my earplugs in, the bike seems to have about 5.25 horsepower less than in the mornings when I ride the same exact route without them. The earplugs don't weigh that much, but it must be just enough to put me over the RMPAIT (Required Minimum Power Acoustic Input Threshold) to effect the performance of the bike. I've written BMWNA several times about this defect in bike design, but they won’t return my calls.

 

Any clues?

[steve.foote]

Interesting outcome.

 

Not directly related, but maybe someone can help...

 

Of late I've been noticing some performance variations in our 12GS that I'm trying to sort out. When I ride to work in the morning with my earplugs in, the bike seems to have about 5.25 horsepower less than in the mornings when I ride the same exact route without them. The earplugs don't weigh that much, but it must be just enough to put me over the RMPAIT (Required Minimum Power Acoustic Input Threshold) to effect the performance of the bike. I've written BMWNA several times about this defect in bike design, but they won’t return my calls.

 

Any clues?

 

Ken, is it possible that they have been calling you back on the days you road without earplugs and you simply can't hear them?

[Wooster]

That's my story and I'm sticking to it.

 

Very impressive, really. If I had half as much mechanical knowledge as Ed, I'd have twice as much as I do now.

BTW, the resonance you mention, is that what causes beneficial back preasure, pushing partially burned gas/air mix back into combustion chamber, getting more hp because of greater than atmospheric preasure packing cylinder ?

 

Wooster w/ more style than substance

 

First cow: "I was artificially inseminated."

Second cow: "No way"

First cow: "It's true, no Bull."

[russell_bynum]

So, in conclusion, at last you might say, there might be some small benefit to removing the cat and stock muffler if you compensate for changes to the exhaust system by changing the fuel curve to suit. Just removing the cat without going the extra step will gain little or nothing unless steps are taken to change the fuel curve.

 

That's exactly what the guys at the dealership told me when we ordered the Remus for Lisa's bike. They said if you just change the pipe, you will not see a performance gain...and you will probably start noticing dips and holes in the power curve (which we did). If you do the exhaust AND a chip, then you'll see a slight gain in performance. I forget how they defined "slight", but I believe it was similar to the gains you saw (from 79hp to 83hp).

[JamesW]

And that's my story and I'm sticking to it as well.

 

I have read these posts with interest and I do agree with those that say show me the proof as in dyno runs, etc. Yesterday I went in search of a dyno and found a shop with one that can do the job. They charge $75/hour and it would take several hours as they have to make several runs to really heat up the motorcycle and the shop is about 65 miles away. Now, it would have cost about $300 for a before and after dyno test and that seems to me not to be productive as I am not in the business of motorcycle performance products design for profit. Hence, I spent $50 and made myself happy or should I say happier.

[Joe Frickin' Friday]

Humans aren't machines. Anybody can look at a stats sheet, but I'd rather hear it from a person's personal perception. I trust that more.

 

So if a LEO, exercising his powers of personal perception, says you looked like you were going too fast, you'd trust that?

 

Personal perception is fine for assessing attributes that are purely subjective (it "sounds better," it "sounds more powerful," etc.). But perception is heavily influenced by one's biases - both personal biases (as the owner, who has a vested interest in seeing a positive outcome as a result of his labors) and general human cognitive biases. As such, I am loathe to trust personal perceptions when it comes to measuring a clearly defined metric - especially when an observer reports a perceived performance improvement where theory and past experience suggest little or no improvement is likely.

 

Isn't that what most bikers want-to increase their riding pleasure?

 

Sure. But if person A mods his bike and then reports (based on his physical perception) that his bike is more powerful, and person B does the same mod and reports (based on his physical perception) that there's no change, then they'll argue back and forth about who's right until the cows come home, just as we're all doing here right now ; it takes a dispassionate, impartial measuring machine to come up with reliable answer (YES, there is more power, or NO there is not more power) that everyone can agree on and use as information in making a well-guided decision.

[JamesW]

Joe, I do agree with you completely. I could sit here and theorize forever on why I think removing the cat does this or that but the bottom line must be where is the proof other than my personnal perseption. That said it should also be nioted that sometimes proof can be distorted to favor one argument or another on any particular subject. For example, where are the supposed WMD?

[Wooster]

James,

 

While WMD are too hot for me to touch, I can agree that the objective vs subjective debate can overlook the fact that we humans respond subjectively to most phenomena. I recall an educationist (a Mr Scriven, Ph.D.) describing how silly it is to assess television's picture via objective measurement (light meter, for example) when true test is viewer satisfaction. So, while I remain skeptical on catectomy's (great word you've got there) utility, I agree that objective data sometimes clouds subjectively perceived benefits (which are real).

I hope the preceding makes sense as that was my intention.

 

Jonathan w/o a joke

[Joe Frickin' Friday]

That said it should also be nioted that sometimes proof can be distorted to favor one argument or another on any particular subject.

 

If the "proof" can be "distorted", then the experiment was poorly designed, either deliberately (to confound the truth) or carelessly.

 

"Deliberately" includes things like ads waving dyno test results that indicate a performance improvement due to a new, carbon-fiber snorkel tube (when in fact the snorkel tube was part of a package that included a new exhaust, performance chip, Techlusion, etc.).

 

"Carelessly" includes things like doing back-to-back tests before and after the mod, resulting in a completely warmed-up (and thus more efficient) drivetrain for the mod test, or not correcting for ambient conditions when before/after tests are conducted on different days (as would be the case for a cat removal).

 

A well-controlled test with significant results - one in which there is a definite, measurable difference in performance, a difference that cannot be attributed to one of a host of other variables - can provide proof that is difficult to distort.

[chrisx]

I have stayed out of this until now but as a long time turbo saab owner, rodder and tuner (2 liter with a modest 230 hp and dyno slip) i have to say sorry, no dyno slip, no horsepower. but beyond that...what does it really give you? what....can't go fast enuff to kill yourself already? the bmw'r dog slow? the engine too quiet for a relaxing cruise?you are free to mod away to your heart's content. but don't expect people who have wrenched for 25+ years to take anyone's word on anything when it comes to non-dyno claims of amazing results, been there seen it, lots of times, and it usually is wrong. we are free to our opinions just as you are. if you are interested in performance you will find that a dyno pull is a very worhwhile experience, you will get a perfect picture of what your engine is doing. how do you even know you did not throw your a/f off? etc... it is not expensive and it is a hoot to do. where else can you rod the sh*t out of your ride in perfect safety. take a sound recording and post it. no one has called you a liar, just an optimist.

[RFW]

I wonder how much of this is wishful thinking. To be sure, you will get a different sound, because the cat does have a minor muffling effect. Replacing it with a straight pipe will also negate its functioning as an antiresonator chamber. And it certainly does produce a small amount of backpressure (even though it has a straight-through exhaust path), so removing it will likely result in a small HP increase.

 

But better cold starting? Let's get real! The ease with which the spark plugs can fire a cold fuel-air mixture has nothing even remotely to do with whatever is far downstream of the exhaust valve. Until the engine is firing, and producing a significant amount of exhaust, there is no back pressure (cat, or no cat!) in the first place.

 

Bob.

[chrisstroh]

I agree, the only thing that might make a bike start faster after removing the cat would be an exteme restriction in the cat, which I guess isn't so. Ihad a 68 Plymouth fury that died on me at a stop sign. I restarted it and it would idle but when I accellerated it would die. I put my hand over the exhaust pipe and wasn't getting much pressure. So I got under it with a hammer and beat on the muffler until I heard a sound change. Apparently one of the baffles in the muffler had broken and was blocking the exhaust. I learned to look for that when my dad did a valve job on his 62 Lincoln because it ran poorly. After all that work he test drove it and it still ran lousy. It turned out to be a clogged dual exhaust. Boy was he pissed!

The points here are good ones, and I'm happy to have heard them because they do make sense.

I'd love to see a before and after dyno test just to clear the water.

Chris

[chrisz]

Guys I think that the cold weather has affected all of us. Lets give each other a break, the mod only cost $50! and its not for sale, but for tinkering. If something works (whether perceived or not) for 50 bucks I'm a happy camper. Used RT exhaust are cheap (another $50) so if the perfomance sucks, it can be brought back to factory specs. God knows, we all have made performance "upgrades" (code plugs, light bulbs, plugs, etc) without spending mucho mulla to verify that those minor mods has been an improvement. If we don't agree with something, just nod your head and smile and if it works for you, great! It'll all come out in the wash in the end.

[JamesW]

Hi chris, you know what? I too would like to see a before and after dyno test. It would be most interesting. I have another thought or theory to ramble on about. The position of the cat in the cat chamber is at a right angle to the direction of flow through the muffler. In fact the exhaust gas exits the cat directly into the left side wall of this chamber then must make a 90 degree turn to enter the muffler. In other words the cat is not in line with the axial center of the muffler but is at a right angle to it. I can see why it is this way because of the space restrictions inherent with a motorcycle. I do question how this arrangement makes for a smooth flowing exhaust system. Did I make sense here?

[chrisstroh]

That makes sense, but for quicker starting it doesn't. The restriction would have to be pretty bad. Interesting though that my RT takes several revolutions to start when cold. What I liked about the catectomy was not only a backpressure issue, but a heat issue on hot days and it heating up my transmission in traffic. My transmission is noisy when fully warmed and thought this would help it in addition to synthetic oil.

chrisSTROH

[JamesW]

Bob, maybe I should try and explain the better starting thing a bit better. The motorcycle started about the same but seemed to idle more smoothly much sooner after ignition. I didn't mean to imply that ignition took place with fewer crank shaft revolutions. Sorry.

[RFW]

Bob, maybe I should try and explain the better starting thing a bit better. The motorcycle started about the same but seemed to idle more smoothly much sooner after ignition. I didn't mean to imply that ignition took place with fewer crank shaft revolutions. Sorry.

Aha! That makes a lot more sense. By the way, are you sure your cat wasn't damaged in any way? A cat with a partially collapsed or plugged core can really cause the sort of problems you were referring to.

 

Bob.

[russell_bynum]

What I liked about the catectomy was not only a backpressure issue, but a heat issue on hot days and it heating up my transmission in traffic. My transmission is noisy when fully warmed and thought this would help it in addition to synthetic oil.

 

Have you done oil analysis of your used transmission oil? And if so, did the results indicate that the oil was breaking down due to excessive heat?

 

(BTW, That's a cheap, easy test to do...I believe most oil analysis places charge about $40.)

 

By all means, do the oil analysis and find out for yourself. In the meantime, I can tell you that I know a few people who have done oil analysis of the transmission oil and it showed absolutely ZERO signs of being damaged by excess heat.

 

Your transmission is noisy when it gets warm because it's a BMW transmission (Getrag, actually) and they do that. Some people have reported reduced noise and better shifting when they switched to the RedLine oil. I haven't tried it, so I can't comment on it personally.

[AZDrifterus]

Re. Heat

I have commuted on a motorcycle almost every working day of the last 5 years.

The last 3 summers I rode an '04 GS and an '04 RT.

With the cats in place, sitting at a stoplight at 115F, the radiant heat from the cat softened the soles of my riding boots, not to mention the hotfoot.

 

I replaced the cats on both beemers (Remus on the GS, 2 Brothers on the RT). I also added K&N air filters and a TFI box.

 

Heat problem solved.

 

Free-flow exhaust by itself, very little change other than near elimination of part throttle, light load, lean surge.

 

Exhaust & K&N, drivability increase - better throttle response, but definitely running lean, especially on closed-throttle over-run (i.e. shotgun blast backfire).

 

Adding Techlusion solved lean conditions and kept performance gains.

 

An added benefit to exhaust mods - I no longer have to listen to the the amazing cacaphony of mechanical noises these engines produce. The exhaust note is louder than the taps, bangs, clacks, rattles, whirs and cluncks.

[russell_bynum]

Free-flow exhaust by itself, very little change other than near elimination of part throttle, light load, lean surge.

 

Did you also eliminate the O2 sensor and install a CO Pot? We installed a Remus system on Lisa's R1100RS and it made absolutely ZERO difference in the surging...but I wouldn't expect it to since the only thing in the exhaust that has any link to the motronic (the thing that actually creates the surging) is the O2 sensor...and we left that in place.

 

 

Exhaust & K&N, drivability increase - better throttle response, but definitely running lean, especially on closed-throttle over-run (i.e. shotgun blast backfire).

 

That's interesting considering that there have been actual dyno tests done where people TAPED OVER the majority of the stock air filter and the result was ZERO change in the power that the motor was producing.

 

Adding Techlusion solved lean conditions and kept performance gains.

 

This is the only thing you've said so far that has any credibility.

[JamesW]

I looked the cat over closely and noticed that a very few passages were blocked. I held a flashlight to one end of the cat and observed light shinning through and it looked to be in very good shape. You know, I asked myself many of the same points raised here like how much of this perceived performance enhancment could be attributed to the rather nice exhaust note and it is only human nature to believe that your efforts have indeed born fruit. All that said I do believe that there are improvements in performance particularly in low end snort and overall smoothness. It is not the difference between night and day but I got my 50 bucks worth.

[chrisstroh]

Oh no!!! I can't watch!!

[RFW]

I looked the cat over closely and noticed that a very few passages were blocked. I held a flashlight to one end of the cat and observed light shinning through and it looked to be in very good shape. You know, I asked myself many of the same points raised here like how much of this perceived performance enhancment could be attributed to the rather nice exhaust note and it is only human nature to believe that your efforts have indeed born fruit. All that said I do believe that there are improvements in performance particularly in low end snort and overall smoothness. It is not the difference between night and day but I got my 50 bucks worth.

As a final "I wonder" comment, I wonder if some of the performance increase you seem to feel has to do with the side effect of the reduced backpressure resulting in a MIXTURE change? In other words, it is possible that the change in backpressure itself is not what is causing what you seem to feel, but the secondary effect of a possible mixture change.

 

The fact that you seem to notice more of a change at low RPM is interesting. One would think that the greatest improvement would occur at high rpm. At high RPM and open throttle, the measured backprssure will be at its highest level (since the motor is trying to pump a lot more exhaust through the cat).

 

Since you mostly notice the improvement at low RPM, where the backpressure difference is more minor, it sounds like something more indirect could be involved here.

 

If that is the case, then this is something that a custom FI chip (that "fattens" the mixture a bit) might also produce.

 

Bob.

[Steve W.]

Found this site where some dyno testing was done on Bmws.

http://www.moto-one.com.au/performance/index.html

Just go to the Bmw pages. Looks believable. Make your own opinions.

Steve (GS with no cat + techlusion)

[ShovelStrokeEd]

I got my 50 bucks worth.

 

That, James, in the end, is what is most important. You made the mod and you are happy with the result.

 

You also fostered an interesting post which gave us all something to talk about.

 

I would really like to see this whole "backpressure" thing put to rest. Since you seem to have access to a welder who will work cheap, how about volunteering your bike for a simple test, or half of one anyway. You will need an O2 sensor bung, available from either a header manufacturer or possibly a decent parts store.

 

What I would love to see is a static pressure measurement in the pipe in front of the cat, say at the O2 sensor location, and another measurement behind the cat made through the newly welded in bung. Running the motor at say 4000 RPM in 3rd gear. If you provide the bike so equipped, I will provide the pitot tubes with proper static pressure probes. A U-tube manometer should be adequate to measure the pressure difference if, as I believe, the cat offers very little in the way of flow impediment. If it is restricting flow, there should be a pretty large pressure differential between the before and after pressures, if not, it will be very small. Simple test and a couple of bucks worth of welding plus a little machining costs for the plugs to carry the pitot sensors.

 

I'm just tired of hearing of this so called back pressure. It indicated a restriction to the flow when, no one has ever given a single measurement to prove that it even exists! At least not here, to my knowledge.

 

I know Mitch does this kind of stuff for a living and he might just save us both a few bucks and give us some numbers for the pressure drop across a typical cat. Doesn't have to be for a BMW motorcycle, any old car or truck data would work.

[steve.foote]

Ed, it's a little dated, but here is an interesting post I found doing a Google search on 'Catalytic converter back pressure':

 

Date: Sun, 04 Apr 1999

From: Robert <rtchafin@earthlink.net>

Subject: Catalysts & Backpressure

 

I made the following reply to Jim C., but didn't realize he'd also posted to the List, so in fairness, thought I'd post my reply to him:

Jim:

 

I agree with many (no make that, "most") of your points, but having had the opportunity to not merely cut apart, but also to measure the backpressure of a number of BMW exhaust systems, as well as probably a thousand or more of those on other automobiles and trucks, ranging from the early ZR-1 and the current GenV Corvette (I designed the C5 mufflers, and developed the full system), to the various 'M'-Class exhaust systems for Mercedes, I believe I know whereof I speak. The catalyst is usually 30%-50% of total system restriction; in some cars, such as the Corvette, which has very low-backpressure mufflers, the catalysts' contribution to restriction can be much higher still. Granted, such metal-monolith cats as Emitec's have fairly low backpressure, but so does the rest of the system on most BMW's, so the cat still makes a large percentage of the system backpressure.

 

I'm not at all disagreeing with you about the effect of backpressure on emissions; in fact, the relatively unsophisticated emissions strategies of the '70's and early '80's relied on backpressure to control EGR. Many Ford systems, for example. used the exh. backpressure as the "signal" in the EGR control system. Nor do I question that there would often be a need to retune the fuel control system to compensate for lower backpressure IF emissions were an issue. But the original question on the List was posed by someone who could care less about the emissions effect of his vehicle modifications, a viewpoint that I share. I guess I made the mistake of not just answering him directly, which is what I usually do with exhaust-related questions. I find there are far too many on the List who have opinions unsupported by fact in a field in which I am something of an authority.

 

Regards,

Robert

Source

[JamesW]

My God Ed, it seems you have thrown down the proverbial gauntlet I think to make this test one would have to have a working cat in the cat box? And that would mean welding the cat back in place? Afraid I must pass on this one as yesterday was garbage day and guess where the offending appendage went?? Well, not where you might think because me being environmentally tuned in I re-cycled it

[ShovelStrokeEd]

James,

The idea is to get another guy, who does have a working cat, to do the same mod to his bike. That's why I said you would perform half the test.

 

Steve,

That is the kind of stuff I'm looking for. 20-30% of the total back pressure, hmmm. Higher percentage if a low restriction muffler is used after the cat just makes sense. I would still need the pressure drop data to see what the real effect on the flow would be. An early conclusion would seem to tell me not much by just removing the cat since changing the entire exhaust to a supposadly lower restriction system (Rhemus) doesn't do more than a 1 or 2% improvment in HP. I gotta go read that source thread.

 

OK, read it. Seems cat removal is worth 5-10 HP on an M5. Given that the materieal is pretty old, an M5 made about 360 HP back then so, a 2.7% gain. Applying the same increase to a R1150RT at 80HP base we wind up with 82.2HP. Interesting to note the gain was all at the top end with some speculation that there would be a drop in mid range torque. Kinda confirms the testing I did way back when.

[russell_bynum]

An early conclusion would seem to tell me not much by just removing the cat since changing the entire exhaust to a supposadly lower restriction system (Rhemus) doesn't do more than a 1 or 2% improvment in HP. I gotta go read that source thread.

 

That's my feeling as well. If a full replacement exhaust without a cat and with a free-flowing can doesn't make any real difference, then how is just gutting the cat out of the stock exhaust going to do any better?

 

I'd love to see data to explain the gains that Tracy is reporting. If the dyno actually does indicate a gain, then we can start the task of figuring out why.

[JamesW]

Ed,

Just a thought. Why not measure the output from the ox sensor which, I would think, would be either a voltage or resistance quantity sent to the motronic unit? One could make this measurement with a simple digital VOM at different engine RPM points between idle and 4K RPM before cat removal and after removal. Then plot the curves as a function of volts/resistance change on the Y axis against engine RPM on X axis. Seems to me this would give an indication of more or less restriction to the flow of exhaust gases. Of course one would have to find a willing candidate that plans to perform a catectomy. This would be a simple test and cost nothing. One might have to disconnect the ox output from motronic to make the measurements but this should be simple enough. Wish I would have thought of this sooner but in truth I really didn't expect to see any note worthy performance change. I still think that the cat IS NOT restrictive to constant air flow through it as the cross sectional area is at least twice on the output end as on the input end. I think what happens when the cat is inserted between the engine output and muffler input a mis-match is created which results in reflected power back to the engine. Similar to what happens when the transmission line that connects an RF transmitter output to an antenna input does not match the impedance of either element. Spent half my life chasing down causes of power reflection with broadcast equipment. I like to think of the head pipes and cat as the transmission line from engine (transmitter) output to the muffler (antenna). This transmission line must be matched or tuned to the connected devices. Now, I'm probably full of the you know what but this is how I think about what I believe is happening.

[ShovelStrokeEd]

OK, first the O2 sensor as a measuring device for flow. No workee. Basically the O2 sensor functions as a switch, it is putting out a constant stream of Hi/Lo transitions, not a steady state voltage proportional to the mixture or, more properly, the O2 in the mixture. The communication stream goes something like this, lean, lean, lean, rich, lean, rich, rich, lean .... ad nauseum. BTW, when this gets out of phase with the Motronic outputs due to lag in the reaction of the sensor, is the prime cause of surging.

 

Now as to exhaust resonance. The resonance pulses from the exhaust system are generated by the abrubt change in diameter of the pipe. They really are a function of the relative diameters of the pipe and its next stage of transition. The primary one of interest in this case is where the head pipes merge into the collector which is well before the cat. These pressure waves are far different from what you would expect in terms of the exhaust flow. They actually travel back up the pipe at the speed of sound. The tuning is controlled by the length (most important) and the relative diameters of the collector and primary pipes (less important). There may, and I repeat, may be a secondary resonance caused by the collector pipe dumping into the newly opened chamber of the empty cat, which, might, be contributing to some better cylinder filling during the overlap stroke. I doubt very much it would have any effect on low or even mid range torque though as at fairly low RPM's of around 3-5K or so, there just isn't that much effect. This phenomenon usually is only effective over a pretty narrow range and at relativly high RPM's where the pipe resonance can be made to cause the pressure pulse to arrive at the portion of the overlap period during which the exhaust valve is nearly closed and the intake has already opened. A look at the valve timing for the oilhead motor places this at a very narrow band of time indeed, as the cam just doesn't provide all that much overlap. Said timing being a big enemy of emissions.

[gratefulJED]

OK, so which software/exhaust/cat bypass was the best bang for the buck for a noob with just a hint of rust on his stock 04 chromed pipe? ?

[steve.foote]

OK, so which software/exhaust/cat bypass was the best bang for the buck for a noob with just a hint of rust on his stock 04 chromed pipe? ?

 

I think you would still be better off to port and polish the heads.

[JamesW]

Ed,

Thanx, that makes sense the part about how the ox sensor communicates with the motronics. So much for that idea. I haven't a clue what is really taking place here but something is.