4 stroke exhaust theory and the clone

[Russell ATV]

Ok, I am looking to you 2 stroke and 4 stroke experts out there. After reading lots of stuff, taking in data from engine gurus and hacks, and applying some simple logic, here is what I have come to observe:

A tuned pipe on the exhaust of a 2 stroke can create a supercharger like effect at specific RPM by creating resonance waves that help pull the exhaust gases from the engine before the intake stroke begins. It also helps pull more fuel/air into the cylinder chamber, effectively increasing it's capacity.

Now, 4 stroke engines have a dedicated exhaust stroke, so no significant supercharge effect. Now, obviously, a very restrictive exhaust/muffler can increase pumping forces restricting power/RPM. But really, comparing an open exhaust (no header, muffler or pipe) to a 2 stage header pipe, what really would be the difference? Perhaps a 5-10% power increase.

Don't get me wrong, more power is more power, just thinking of ways to save a buck and get the same power. Here is what I am thinking:

I have torn down a Clone/Honda exhaust to see where the restrictive elements are. I will post some pics to show the exhaust path and a section analysis. By porting the muffler, I believe I can change the exhaust flow and create a chamber not too unlike the 2 stroke tuned pipe.

Sound reasonalbe/logical???????

Russ Barrow
Russell ATV

 

[Russell ATV]

Ok, here are the pics.

Picture 1 is your common variety muffler with shroud.

Picture 2 is has the shroud removed. Notice that round circle on the back corner.

Picture 3 has the first stage chamber of the muffler, the exhaust flows through the header, then through the holes on the header pipe. The top of the pipe is capped, and forms the circle from picture 2

Picture 4 shows the baffle, where the gases from the first stage pass through the holes in the right corner to enter the second stage chamber. The holes on the left corner is the entry into the third chamber.

Picture 5 shows the profile of the third chamber/baffle. This is the problem. The third chamber is tight and small. Gases have to bend through 180 degress of bends twice, then the 90 degrees out of the muffler.

Blowing air through the muffler, I can hear my blower strain. So, An idea I have is to drill entering from the exhaust output hole of the muffler (down into the baffle). I have been able to drill through the third chamber opening a large hole both into the first and second chamber. Effectively eliminating the baffle and opening up one large chamber. Running the same blower test through my now "ported" muffler, there is almost no difference from it versus a 3/4" tube of 12".

As for the sound it makes on the engine, more of a rasp and slightly louder than before the muffler was modified. Nothing close to the extremely loud pumping sound of a 2 stage header.

As far as drivability, I cannot tell the difference in power from the header to the "ported" muffler. I do not have a dino, so my butt is all I have.

Russ Barrow
Russell ATV

 

[Kenny_McCormic]

Your a little off on the 2 stroke thing,

I love gutted mufflers.

 

[jr dragster T]

Nice observation about the restrictive part's on a stock clone. As far as I understand the first small stage of a header is to keep the torque up and the larger section's are there to help it flow on the top end.