FOR ALL YOU EXHAUST EXPERTS  By  rcq92130 (Read 1,554 times)

I have been wondering why they are made that way myself. It should be cheaper to run a large pipe all the way, rather than to put a smaller pipe on the ends. Makes me think there may be a good reason why it's made that way. the air coming out of the head would slow down and expand upon entering the larger pipe. Hitting another small pipe at the other end would increase velocity and pressure. The larger pipe may create a vacuum of sorts, helping to pull air out of the head, and the whole system might break up the impulses of air, bringing the outlet pressure down to an average of the two pressures, between pulse and no pulse. I am looking forward to reading the replies you get about all of this mysterious plumbing.


(Edit 8-26-14
Here's an article about 4 stroke exhaust telling us why they believe the headers have steps in them:

"Another popular trick for high RPM applications is the use of a stepped header. This is where the header steps to a larger diameter a few inches from the exhaust port. Some pipes use multiple steps along the length of the header. Typically, there is a step where the exhaust port ends and the exhaust pipe begins. This is left as a step, rather than making the pipe diameter match the port diameter to help prevent reversion, that is prevent exhaust gases from flowing backwards into the combustion chamber after the piston reaches TDC. If the pipe is designed to be used at high RPM's, then the exhaust gases may not have enough velocity at low RPM's to prevent reversion, so this step helps prevent it, thus helping power at low RPM's. There have also bee anti-reversion cones used in the past, it is like a funnel placed inside the entrance to the header to further help prevent reversion. Steps placed further down the pipe create pressure drops in the flow of the gases, and can sometimes help increase power at higher RPM's depending on where they are placed along the pipe. "
See the original article at www.thumpertalk.com/topic/798327-4-stroke-exhaust/ )

My thoughts , a engine is just a big air pump , more air in and more air out makes HP . I personally think that the pipe should be big from front to back , if you need back pressure it should come from the muffler , I remember seeing on expensive sport bike mufflers a bunch of thin plates that bolt on right at the outlet with washers between every plate as spacers , yhat way you could add or remove discs to tune the pipe for your bike , but that just my 2 cents

Keep the NCY one with the bigger outlet by the Flange.
Alleyoop

THANKS, GUYS!!!!!!!!!!!!!!!!!!!!

That is the knowledge and advice I was hoping to get. Appreciate it very much.

Pmaulew is that photo not of a 2 stroke muffler ? If it is that is a whole different ballgame as the engine fires on every stoke and they don't even have valves .they use a reed valve , like a little flat tin plate , and then the scavenging of this type of pipe would be needed

Have another header ordered - this one the same diameter end to end.

Theory has it what I received is a 50cc header (the small pipes perhaps adequate for that small an engine), not the 150cc "Performance header" it was described to be.  Maybe an innocent mistake by the retailer - have not yet heard back from them, so can't yet tell.

New header will not arrive for a week or so, so I'm going dark till then.  Thanks again, everyone, for helping with this (and the other)issues!

On one header I had the smaller pipe inside ran all the way, It only looked like it would transfer into a bigger pipe after about 3 inches.
But when I cut the header in several places to check I saw that it ran all the way to the muffler.
I wouldn't be surprised if it's the same with this one!
You might as well use the original. No difference...