Anyone replaced the catalytic converter with straight Y-pipe

[Beemeridian]

33

[dilligaf]

Yellowjacket wrote,

Since it is the top I will have to remove, will there be more heat through the resulting quarter inch plate?

My slightly educated, somewhat shade tree mechanic opinion is....The "guts" of the cat are what hold in the heat to burn off all of those nasty earth destroying hydrocarbons, and since you're removing the "guts" the exhaust gasses will flow more freely with much less heat stored in the pipe.

It sounds like you have a very tough and time consuming project on your hands, but i think no matter how it turns out the results will be greatly appreciated. The topic of "gutting a cat" has been brought up time and time again on this and other boards, maybe now we'll finally find out if its worth it and if so the best way to do it.

[Doug t]

I agree with yellowjacket. Good luck and keep sending those pics!

[Beemeridian]

33

[djwaudio]

What about keeping the cat. I hate riding behind smelly toxic bikes.

[dilligaf]

Yellowjacket,
I know i over simplified it, i was just thinking that without the heat sink cat it should run cooler regardless.

What about keeping the cat. I hate riding behind smelly toxic bikes.

Djwaudio,
How many "toxic bikes" do you think it might take to equal one black smoke belching, pine knot burning, i get three miles to the gallon semi?

just curious.

[Guest]

Beware with your knowledgeable advice Dilligaf, Dallara has his eye on you and he enjoys a good meal.

Mike

[Beemeridian]

4

[jm1515]

I am grateful to you, djwaudio, for stating what I believe most of us, who are a bit more caring about the earth, and our riding experiance than those who disregard laws with willful abandon however, I would be equally grateful to reiterate that this project is intended only as a alternative to the expense of a straight-pipe and therefore aimed at those who are going to do it anyway.

Please remember that the cat for this experiment was kindly, and may I add generously, donated by dilligaf for the purpose of research. I still have, and fully intend to continue using, the converter on my '05 R. I shall to the best of ability (and wallet) quantify, in acceptable scientific cirteria, the expense, procedure, before and after: sound levels, and emisions-as comparable to the govts. expected, published levels.

...yeah, right.....

[Beemeridian]

3

[dilligaf]

Beware with your knowledgeable advice Dilligaf, Dallara has his eye on you and he enjoys a good meal.

Oh great, another dallara groupie.

[fritz]

I'm thinking of replacing the cat with either the staintune collector or remus premuff or Y pipe. The service manager of the dealer I use says when you swap the cat for an aftermarket exhaust most yield a lot of popping on decel, he thinks because they are not sealed tightly (where the header joins the cat I think). My question is, what kind of hi-temp sealant do you recommend to seal the exhaust system? The service manager said he had heard of one that was supposed to be especially good that turned to a ceramic when it got to high temp, but he couldn't remember the name of it. Most of the high temp ATV sealants are silicone-based; it would seem they would seal better than anything that becomes rigid (ceramic).
Other question: when you add an aftermarket can, or lower the can, don't you have to remove the can each time you remove the rear wheel (with the bike on the center stand)? Seems this would be a pain in the butt when out touring. Thanks for any help. Dave

[DJ Downunder]

Here's my thoughts..(I may be wrong)...when you back off and use engine braking..exhaust gasses get sucked back towards the hot headers.

If the system is less restrictive it alowes it to happen more..eg..either running with no can..or..running with a sports can..or..running with a Y pipe.

I was told that this gas that gets sucked back has some unburned fuel in it and it re-ignites when coming in to contact with the hotter parts of the exhaust..thus causing the pop,pop when backing off.

My bike still has the cat but no can...it did it a little in the beginning and I asked my mechanic if it causes any harm...he said..no..no harm at all.

I don't notice it doing it any more..not sure why...anyway..back to your question...I don't think it's a seal issue..but then I may be wrong.

I know someone that will know for sure....come on Dallara...

DJ

[fritz]

Thanks DJ,
I really don't mind the popping and blubbering myself. In researching some of the aftermarket stuff, I read on one distributor's (Motosports Network) site that Staintune recommends the following:
" While all Staintune exhausts have close tolerance fittings, it is always recommended to make an airtight seal with the addition of some High Temperature RTV sealant (oxygen sensor safe if needed). If you fit the system together without it and notice weeps of black carbon build up at the joints, the pipe can be removed, the connections wiped clean and RTV sealant applied later if needed."
Being as I'm a novice wrench (but want to things like this myself), I don't want to screw it up too bad. I'm not totally convinced I want to take that cat off. I actually kind of like what you have done with that shorty pipe tip off the cat. Maybe I'll try that first. Dave

[DJ Downunder]

Cool...give it a go...just realized your question was more about the sealant than the popping....ooops

I'm sure Dallara or someone will know about those sealants..

DJ

[darthrider]

Any auto parts store will have the proper sealant.

[dallara]

A couple of quick things...

First off, I have the Staintune collector "box" and I have not noticed any "tinny" sound to it, even when I used it with the stock muffler... Now I run a Neptune muffler, and I still notice no "tinny" sound...

Might just be my hearing, though...

The thickness of the "housing" of the stock catalytic converter is there for two reasons.... Yes, to retain as much heat as possible - 1.) to try and get the cat up to temp as quickly as possible, as cats need to reach a high temp to operate 2.) To try and "trap" the heat as much as possible inside the cat so it doesn't heat the outside air as much as it could, an "insulator, if you will.

Of course, this makes it heavy as all get out.

On DJ's questions about the scavenging, etc. of exhausts... All exhaust systems have "ranges" where they work most efficiently, and by definition, hence also have "ranges" where they work very inefficiently... Such is the nature of a pressure wave and resonant device. At certain RPM's and exhaust pressures the pipes work well to keep any exhaust gas from being drawn back into the combustion chamber, but at other rev ranges they do not do a good job of this and some exhaust gas is reintroduced to the head... This doesn't matter if it is the stock exhaust or a modified exhaust. Further, DJ, even with the cat in place, there is always some exhaust gas upstream of the cat, and so in certain rev ranges it will be drawn back into the combustion chamber. It's pure physics, and is irrefutable. I imagine BMW "tunes" the stock pipe to operate best in the 3,000 to 4,000 RPM band, as that is where the bike will spend most of its life. At lower RPM there is most likely a lot of exhaust and fresh charge mixing in the combustion chamber... And at higher RPM there is little, but the exhaust system "chokes" the breathing a bit.

Actually, any pops and backfires anyone experiences is *NOT* exhaust gas getting back into the combustion chamber... Quite the opposite. Those events are always the result of some *UNBURNED* fuel-air mix getting into the exhaust pipe... And then igniting there. This usually happens when an exhaust system is *overscavenging* - i.e. producing such a strong negative pressure wave in the pipe that some of the incoming fuel-air mix coming into the combustion chamber on valve overlap is drawn into the exhaust system. This is very common on "over-run", when decelerating, as road speed holds RPM high relative to throttle opening (i.e. you have closed the throttle to slow down, but the bike is still rolling along). Due to intake ram and exhaust negative pressure wave effects a relatively high concentration of unburned fuel-air mix is drawn into the pipe, where due to heat and expansion, it spontaneously ignites, causing your pops and backfires...

As for sealing... As of yet I have not found it necessary to use any sealants running my stock R-1150-R head pipes, Staintune collector "box" and either the stock muffler or Neptune. Personally, I abhor exhaust sealant compounds, as in my experience they often cause more problems than they solve. I simply make sure all the junctions are clean and *ROUND* (very important...), and that the clamps I use have good, clean threads and are operating as they should. I use a *VERY* tiny bit of high-temp grease, wiped on *VERY* lighly with a fingertip on all the joints so they can slide together to the proper depth, assemble the exhaust slowly and carefully - with all the junctions loosened aft of the head-to-head-pipe connection (which should be tightened first, if it was ever loosened) until everything is fitted in place... Then I start tightening the most upstream clamps first, keeping everything aligned and in place, and finishing with the aft-most clamps last... Tightening up the muffler hanger bolt after everything else.

So far I have as yet to encounter any sort of exhaust leak or weepage.

Hopefully this answers a few questions...

Oh, and dilligaf... You don't have to worry, or be jealous, either...


Cheers!

Dallara

[fritz]

Thanks for all the info everyone. I'll digest it. Dave

[Beemeridian]

4

[bikermeow]

Went down to see my bike tech today, asked about a Y-Pipe. Was told that the Y-Pipe will improve top-end performance, consumption and acceleration. Downside? kill the environment and emit more heat and a more powerful exhaust blast, which may cook the rear left signal light, and toast side panniers.

Any views on whether it's worth it to take the plunge?

Cheers

Meow