catalytic converter mufflers

BarelyAWake · Mar 5, 2010

Ever wonder just what was inside the newer style "catalytic converter muffler"? The one with the domed endcap & welded together so ya "can't" take it apart?

Well, I did lol and as I needed the headpipe for a different project I figured I'd go ahead and chop up the rest of the now-useless muffler

As you can see the exhaust is forced through the catalytic converter unit first with no possible alternative route - then it's allowed through the baffles, exiting only after a convoluted S turn to be able to go out the tailpipe.

Verdict? Drill away as much as you want on that endcap - while you might make it slightly louder by bypassing the tailpipe, you will not see any significant reduction in back pressure as the exhaust will still be forced through the honeycomb and the baffles. Additionally as 2 strokes are known for carbon build up - I'd bet that honeycomb would clog up pretty quick.

Solution? Don't waste yer time on the thing - if yer after performance, get an expansion chamber FTW

edit: as it turns out - ofc there's more than one type of catalytic muffler, check this thread for another style: http://motorbicycling.com/f13/catcon-muffler-mods-17098.html Thanks ZRTMWA (^)

oldspeedsi · Mar 5, 2010

yep 2 stroke should never have a cat plus a good pipe sounds amazing even on a 50 or 66 cc china motor

K.i.p · Mar 5, 2010

Just a quick thanks for the "biopsy". I have the older style but this is still interesting and informative.

diceman2004 · Mar 8, 2010

wow , they actually have a real cat design , i highly doubt they platnum plate them though , id,e like to know how much it actually reduces emissions . can,t knock em for trying though , its something they have to do to try and keep em legal .

yamahonkawazuki · Mar 29, 2010

diceman2004 said:
wow , they actually have a real cat design , i highly doubt they platnum plate them though , id,e like to know how much it actually reduces emissions . can,t knock em for trying though , its something they have to do to try and keep em legal .

Aye ive got one of these from BGF. i removed hte disc from lower end. left everything else in place. pulls harder i notice. and top speed isnt hardly touched at all drn2

Humsuckler · Apr 2, 2010

yeech.. i have one of these pieces of junk that came with my new kit. i bet its gonna suffer pretty bad lol

BarelyAWake · Apr 2, 2010

The solution lol;

"I needed the headpipe for a different project" and that's the result

It's a modified SBP expansion chamber, ported stock pipe & extended glasspack silencer. While the spring retention system on the SBP manifold is great and reduces metal fatigue - I couldn't bear to have the blue hi-temp silicone on my vintage ride... it just kinda clashed and Ima slave to fashion I guess. The extended glasspack quiets the exhaust to roughly equivalent to stock (sounds different/better - but no louder) and other than being 6" or so longer has little/no effect on backpressure as it's a clear passage straight through.

It's a pretty easy mod (glasspack) as it's simply 2" aluminum conduit, a chunk of metal window screen, a lil fiberglass insulation stolen from my wall & a coupla pop rivets, the stock head pipe slid right in to the expansion chamber with a lil chunk of the SBP system as an adapter

(yus, I still need to trim & paint the one lil exhaust clamp) o.o

I liked how the curvature of the stock pipe pretty much matched the bike heh *shrug*

silverbear · Apr 2, 2010

What I especially don't like about these catalytic mufflers is that they get really hot, much more so than the old mufflers. They discolor quickly for that reason. Wish the expansion chambers cost less, but I am going to have to give one of those a shot. Anyone have experience with the poo poo muffler/pipe?
SB

silverbear · Apr 2, 2010

Barely, that looks great!
SB

BarelyAWake · Apr 2, 2010

To the best of my knowledge the poo-poo is exactly the same "muffler" as stock - simply a longer pipe... so if anything the performance would be the same/decreased, the sound a bit quieter tho.

Yes, the SBP system is a lil pricey to just cut up willy-nilly, but I really love the performance gain & the silencer style... there'd be nothing wrong with moddin' some inexpensive pocket bike expansion chamber tho - sure it'd not be quite the same, but fer what, $25 or so? It'd cost the same as the poo-poo and only require a lil fab skill...

Of which you've plenty to spare silverbear - I've seen yer work FTW

silverbear · Apr 2, 2010

I may just try that with the pocket bike exhaust... thanks for the tip.
SB

Humsuckler · Apr 2, 2010

oh yea pocket bike exhausts are essentialy nearly the same as a SBP one!
and they are usually dirty cheap too.

silverbear · Apr 2, 2010

Humsuckler said:
oh yea pocket bike exhausts are essentialy nearly the same as a SBP one!
and they are usually dirty cheap too.

That's good to hear. Have you tried it? Any particular one you'd suggest? I was looking at this on ebay to experiment with...Item number: 280480849958
it's on sale for ten bucks with another ten for shipping. Can't get much cheaper than that if it would work. I have no doubt that the SBP exhaust is a good one, but I never seem to have the money for one. This pocket bike one has to be better than the stock catalytic kit pipe. Might be worth trying.
SB

silverbear · Apr 2, 2010

I went ahead and ordered it and will chalk it up to "Research and Development" or in other words, tinkering. I have no idea whether I can get this thing to fit or if it will work, but no doubt I'll get twenty bucks worth of entertainment out of it. I'll let you know what come of it...
SB

Humsuckler · Apr 2, 2010

you know.... if you cut the belly weld on that (right in the middle of the fattest part) and rotate it 180 degrees and have it rewelded youd almost have the same belly as the SBP....
id show you what i mean with paint if you dont understand

BarelyAWake · Apr 2, 2010

This un?

HP Exhaust Pipe for 49 cc Super Cat Eye Pocket Bike - eBay (item 280480849958 end time Apr-17-10 15:44:13 PDT)

Tho a great deal no doubt, I'd poke around a bit more on the off-chance there'd be one with a shape that conforms a bit better, perhaps with more a bend in the chamber itself? So much depends on the build ofc, but thanks to many ppl's efforts we know optimum head pipe length is between 9-12" (depending on desired power band effect);

Ghost0 said:
...These engines have a powerband in the 4 to 6 thousand rpm range. To properly tune a scooter/pocket bike pipe for one of these engines, the recommended distance from exhaust port to the start of the expansion chamber is about 12 inches. This can be altered plus or minus an inch or so to correctly tune it to your gearing and riding style. The attached photo illustrates how to measure your header length*.
http://motorbicycling.com/attachments/f13/988d1213632614-expansion-chamber-header-length.jpg

*Good readin' here: http://motorbicycling.com/f13/expansion-chamber-1467.html#post14405

...so that gives you quite a bit of "wiggle room" if you cut the pocket bike head pipe off and use the stock (ported) one like in the pic - we all know how simple it is to tweak those to clear pedals etc.

The only problem I can think of is inner and outer pipe diameters, when I altered my SBP system I had it right there - the coincidental matching of the stock head pipe's OD to the SBP ID was one of the reasons I did the mod, knowing the expansion chamber's performance made it worth the cost, to me - for that particular build.

The pocket bike pipes are obviously "designed" for 50cc engines, the math is somewhat critical for optimum performance - yet even a generic expansion chamber modded to fit w/a approx 12" header will be so much better than stock it's worth the effort in my opinion *shrug*

It's this effect we're after for those that may not know;

A two-stroke

silverbear · Apr 2, 2010

Yeah, that's the one I ordered. I was figuring on running it under as you did and thought that I could do some bending to the pipe since it says the exhaust is aluminum. Although come to think of it aluminum doesn't bend all that well. I could run it further back and cut off the header on the exhaust a bit, and make the sharper bend with exhaust flex pipe maybe. Twelve inches on the header total, eh? I hadn't considered that and may end up long. Well, we'll see if there's a way to make it fit once it gets here. Either way I'll know more about than I did before, right?
SB

BarelyAWake · Apr 2, 2010

lol yea - defo, forgive me, I had gone and typed alla that bfore I saw you had ordered it already

I like the silencer style and by cutting the headpipe it comes with & adding yer own I think it'll work well - the 12" thing is optimum, but does little good if the pipe wont fit w/it so w/e works I figure.

The hours of "entrainment" whilst tinkerin' outa be worth the twenty bucks anyway as ya said

Cabinfever1977 · Apr 3, 2010

These black mufflers use pallidum instead of platnum and is much cheaper but does about the same thing. I drilled the small inside holes toward the cap larger,works better but also a little more noise.

Also heres a pick i found of one cut in half.

silverbear · Apr 3, 2010

Cabinfever1977 said:
These black mufflers use pallidum instead of platnum and is much cheaper but does about the same thing. I drilled the small inside holes toward the cap larger,works better but also a little more noise.

Also heres a pick i found of one cut in half.

Does that black one get really hot, too? I noticed that the chrome one discolored to a blue tint pretty quickly and gets very hot. I think that is due to the restrictions and designed that way to further burn up the exhaust gases. My mix was good, by the way, and I've heard others say the same thing about being very hot and discoloring. Easy to burn your ankle on that one.
SB

catalytic converter mufflers

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