Tinkering with stock exhaust

[willis617]

My suggestion would be to just cut the stinger. The reason for this is because the exhaust with the 3 holes usually has a washer welded over the end of it with the bolt used to secure the end cap welded to the washer.

I get what your saying, but without removing the baffles and shortening header tube there will be no scavenging effect that Street Ryderz spoke of, and i think this is what results in the improved torque?

I should be able to come up with some other way to attach the end cap

 

[CrazyDan]

It can always be welded back on.

 

[LewieBike]

OK this is an otherwise stock 48 cc, but I just drilled the stinger pipe, making 4, 3/16" holes down near the endcap end, and there's a minor bit of low end pull improvement.

My engine would sort of lean-bog a small amount while transitioning up to 3000 rpm, it now pulls through that lean spot without sagging as bad. If anything the exhaust is a slight bit sharper sounding now, not much louder.

All this with two small drillings @ 90 degrees to each other.

 

[gary55]

I can see where some scavenging can be picked up by cutting the pipe above the holes and the stinger short as well by going from a small volume to a larger volume as the exhaust leaves the pipe without holes. With the singer and the other pipe dying in the same part of the muffler chamber beyond the baffles their removal becomes a mater of choice rather than function. All of you scavenging has already happened. For it to work on a basically straight pipe like these I think you would need more flow capability through the end cap than the initial exhaust tube.

 

[Street Ryderz]

I can see where some scavenging can be picked up by cutting the pipe above the holes and the stinger short as well by going from a small volume to a larger volume as the exhaust leaves the pipe without holes. With the singer and the other pipe dying in the same part of the muffler chamber beyond the baffles their removal becomes a mater of choice rather than function. All of you scavenging has already happened. For it to work on a basically straight pipe like these I think you would need more flow capability through the end cap than the initial exhaust tube.

Taking out the baffles is minor but still does make a difference,without them seems to run cleaner maybe due to less turbulance and quicker fill rate.If you've done porting other than just clean up and corrections then yes the bottom will need a couple holes.and maybe even a larger stinger dia,though if a stock pipe is say 19-20mm I.D. at best then .58-.63 of that would be 11mm on the low side and 12.6mm on the high side so they aren't bad even stock dia should work in theroy.

 

[gary55]

I get the quicker fill rate and the turbulance thing, but come on now Bro. You know that the .58 to .62 is specific for expansion chamber design allowing for just enough back pressure to aid the return pulse. If your goal is strictly scavenging then ideally you want the stinger end to be at least slightly larger than the head pipe, but not so big as to suck the charge out. At least this is how my head is wrapping around this.

 

[gary55]

I guess if you could cut the head pipe off flush with where it enters the muffler tube, gutted the baffles and left the stinger alone you could get somewhat of a expansion chamber effect.

 

[Street Ryderz]

I get the quicker fill rate and the turbulance thing, but come on now Bro. You know that the .58 to .62 is specific for expansion chamber design allowing for just enough back pressure to aid the return pulse. If your goal is strictly scavenging then ideally you want the stinger end to be at least slightly larger than the head pipe, but not so big as to suck the charge out. At least this is how my head is wrapping around this.

That's true,that stinger size would be ideal for a tuned pipe and this really wouldn't be tuned but rather a compromise.It's hard to say forsure if their is a slight chamber affect because it would be so small and hard to notice but I do notice a much cleaner sounding burn with little change in volume.I think that when the combustion pressure exit's with vacuum behind it that first part hits the canister and pressurizes it above that of the end of the wave so as to revert it just like a chamber does just not with the same volume or velocity.Because like you said if there is not enough a good portion of the charge will be lost shorting the cylinder fill every stroke and make no real power and terrible responce.

 

[willis617]

Thanks Street and Gary for your imput!
So the consensus is, remove baffles, cut stinger 1 inch above end cap, and cut header tube where it enters can?

 

[gary55]

Thanks Street and Gary for your imput!
So the consensus is, remove baffles, cut stinger 1 inch above end cap, and cut header tube where it enters can?

Hay Willis. I'm just thinking out loud trying to wrap my mind around what is happening in there with diff. mods. So I'm just thinking. Ryderz has a lot more hands on experience with tuning exhaust systems. If I were you I would try it the way Ryderz suggested it first. See if it suits your needs. You can always take more off the head tube later if wanted.