Catalytic converter removal

[Beemeridian]

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[Jammess]

Hi Tracy,
Catalytic converters are not restrictive to exhaust flow so they don't increase back pressure. Therefore, removal of the cat element can't have any affect on engine performance. Now if you remove the complete cat/muffler assembly and replace it with a tuned exhaust system you may very well see a performance improvement because back pressure is reduced but this is a different scenario than just removing the cat element and keeping the stock muffler assembly. Again, I removed my cat element to reduce heat build up under the transmission and it is debatable if I really accomplished anything where heat is concerned. I like to think I did but don't really know. So, I most likely wasted my 40 bucks but I didn't hurt anything either so what the hey. Bike sounds a bit more throatier and I like that but throaty sound doesn't equal performance increase. I removed the stock mufflers from my '07 Mustang GT and replaced them with a pair of Rousch echo chambers mainly for sound and they do make the small block V8 sound bitchin and supposedly performance is increased but I didn't have a dino test performed so can't say for sure and I can't tell for sure that the car performs better but that 4.6L Ford V8 do sound tough when she hits about 6K RPM or so.

[sattwood]

An interesting experienment that I tried was to leave the cat in, but remove the muffler - what I found on my 02 R1150R was that there wasn't much noticable change in sound. The Cat was so restrictive that you didn't need the muffler.

I ultimately removed the Cat with a Y-Pipe I got for about $100. Now there's less heat and the bike has improved mileage (about 25 miles per tank).

[Beaze]

An interesting experienment that I tried was to leave the cat in, but remove the muffler - what I found on my 02 R1150R was that there wasn't much noticable change in sound. The Cat was so restrictive that you didn't need the muffler.

I ultimately removed the Cat with a Y-Pipe I got for about $100. Now there's less heat and the bike has improved mileage (about 25 miles per tank).

Where did you get a Y pipe for $100 at?

[Remow2112]

I had a 92 Stang that I pulled the mufflers and just ran straight exhaust through the cats. Sounded pretty nice. Cats especially as they get older get very restrictive.

I also want to know where I can find a y-pipe for 100.


Thanks,
Dan...

[boxermania]

Jammess

First the facts......cats are restrictive, some more than others. In the case of our bikes they are an early design and are fairly restrictive, case in point the reference made by sattwood a couple of posts back. The ones fitted to the R1200R are significantly less restrictive and along with improvements in the fuel mapping account for the HP increase.

The other fact is if they are not restictive how can you explain that if in a sock system if you remove the cat, or the guts for that tter, the pressure waves at the end of the muffler increse significantly.

I do say that removal of the cat, in our bikes, does improve the operation and response of the engine as I've seen it time and time again. The power gain would be difficult to measure as not only arethey small but will also depend on the state of tune of the bike.

Like I said before to each it's own.......

[Jammess]

Hi Boxermania,
When I first removed my cat I thought I detected improved performance and started a thread on bmwsportouring.com on this subject. One of the tech moderators pointed out that because the cat on these bikes are non-restrictive it is doubtful any actual performance improvement actually occurred. I did some more investigating and I now agree that any performance gain was probably in my head and reinforced by the nice sound. Also, plugging of a cat converter will not happen if unleaded fuel is used in an engine in a proper state of tune. I have also read that some additives like Mystery Oil are suspect in promoting plugging of cat converters. And one must remember that all devices like catalytic converters have a performance life and won't last forever so I am not sorry for the removal of the little beast just like the unsightly carbon canister.

Can you show any proof like results from a dyno test before and after cat removal to substantiate performance improvement? I wish I would have taken the time to have my bike run on a dyno at the time. The HD dealer had a dyno and charged $50 per test. Well, I'm not going to re-install the cat to find out.

[TracyPrier]

Perhaps I need to clarify something here.

I did not find any increase in POWER by removing my CAT... if it came across like that then apologies.

What I found was better running (engine not labouring so much, smoother idle) and better fuel economy

I agree that to get more actual horsepower you would need to do more than just remove the CAT and my personal view is that if I felt the need to do that I probably had the wrong bike in the first place

cheers
Tracy

[boxermania]

Jammess

Regarding HP increase, a dyno test would prove inconclusive as the dyno repeatability is in the 2% to 3% on the better ones. Assuming 75 HP at the crank that would be equivalent to just under 1.5 HP.....

I'n all fairness, I don't want to pursue a long winded discussion. Removal of a exhaust restriction will allow better engine breathing, even though the Motronic system in our bikes is fairly rudimentary it does have some latitude to adjust the mixture, specially in closed loop operation (steady state conditions when the O2 sensor is in the loop). So it is understandable when the removal of the cat might yield some minor gains in mileage.

If your bike has the cat off, look and see if the CCP is installed (the yellow one) in the fuse box. If so, go ahead and remove it, cycle the ECU and see how the bike runs.....I'll venture to say it will feel stronger and crispier on the throttle.....just something to chew on.......

[TracyPrier]

I can add here that my bike is a New Zealand market bike which FROM THE FACTORY has:

No CAT
No O2 (lambda) sensor
No CC Plug

cheers
Tracy

[Jammess]

Hi Boxermania,
I tryed it without the code plug and immediately noticed an unburned fuel or strong gasoline smell in the exhaust. The bike also seemed to idle smoother and was also maybe a bit peppier. So I took a test ride and noted a tendency to backfire loudly when rolling off the throttle so I decided things were better with the ccp installed. I later installed a Techlusion with Autolite AP3923 plugs and all is well. Starts right up, idles very smooth, no surge, good gas mileage (42 mpg 2up), likes mid-grade gas and sounds good as well. I still say the cat is non-restrictive. Look at the physical construction of the cat. It is like a large honeycomb and I bet the free flow cross sectional area of the cat is at least equal to the cross sectional area of both the input and output ends. Hence, not restrictive. In fact I'll even make you a wager.

[OU812]

Jammess

First the facts......cats are restrictive, some more than others. In the case of our bikes they are an early design and are fairly restrictive, case in point the reference made by sattwood a couple of posts back. The ones fitted to the R1200R are significantly less restrictive and along with improvements in the fuel mapping account for the HP increase.

The other fact is if they are not restictive how can you explain that if in a sock system if you remove the cat, or the guts for that tter, the pressure waves at the end of the muffler increse significantly.

I do say that removal of the cat, in our bikes, does improve the operation and response of the engine as I've seen it time and time again. The power gain would be difficult to measure as not only arethey small but will also depend on the state of tune of the bike.

Like I said before to each it's own.......

Indeed. I had the Remus can and Y pipe. BIG difference. Take the can off and no low end. No restriction is not a good thing. Takes away the low end with which the Boxer is all about. Run W/O the can (keeping the Cat) and according to DJ sounds nice and less weight.

[Jammess]

Agreed, no restriction is not necessarily a good thing. However,It is the stock muffler that provides restriction not the cat.

[NoRRmad]

I still say the cat is non-restrictive. Look at the physical construction of the cat. It is like a large honeycomb and I bet the free flow cross sectional area of the cat is at least equal to the cross sectional area of both the input and output ends. Hence, not restrictive. In fact I'll even make you a wager.

Pulse waves from the exhaust valves will bounce back up the pipe, reflected off the walls of the cat. This reduces flow upstream of the cat. And even though the cross-section area of the honeycomb in the cat is large, the boundary-layer flow in the honeycomb is restricted because flow immediately adjacent to the metal walls of each honeycomb cell is substantially reduced, producing only a small area in the middle where the flow is relatively unrestricted.

[Beemeridian]

11

[OU812]

I still say the cat is non-restrictive. Look at the physical construction of the cat. It is like a large honeycomb and I bet the free flow cross sectional area of the cat is at least equal to the cross sectional area of both the input and output ends. Hence, not restrictive. In fact I'll even make you a wager.

Pulse waves from the exhaust valves will bounce back up the pipe, reflected off the walls of the cat. This reduces flow upstream of the cat. And even though the cross-section area of the honeycomb in the cat is large, the boundary-layer flow in the honeycomb is restricted because flow immediately adjacent to the metal walls of each honeycomb cell is substantially reduced, producing only a small area in the middle where the flow is relatively unrestricted.

I knew we would agree on something one day.

[Jammess]

Me thinks we have reached the point of diminishing returns

[boxermania]

Beemeridian

You are absolutely correct, everytime a gas flow (or liquid for that matter) which has a certain amount of energy due to velocity and heat changes direction there is a loss of energy/velocity associated with it. Unfortunately the need to meet environmental regulations, design, cost and packaging considerations place restrictions on the solution at the expense of engine operation and efficiency.

Can you say....."you can't have your cake and eat it too" or "robbing Peter to pay Paul"

BTW, kudos on the nice picture and the flow path arrows....which program did you use?

[Beemeridian]

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