Check it out

[Hellion]

So then that begs the question if the following rings true:

I THINK it goes something like this:
Longer pipe = power at high RPM
Shorter = power at low RPM
Larger diameter = power at high RPM
Smaller diameter = power at low RPM
You have to fine tune the length vs the diameter.

???

 

[bob58o]

So then that begs the question if the following rings true:



???

I agree with the diameter, but I always thought shorter pipes are better for higher RPMs and longer pipes are better for lower RPMs.
I bought the longest pipe I could find for the 420cc. I was told the pipe won't do much past 5k rpm by Robertson Torque Tubes. I guess they are the leading manufacturer of 4 stroke kart exhaust.

But yes I agree, finding the correct diameter and length you can make the engine breath as efficiently as possible at a certain RPM. I've also read about trying to match the displacement to the volume of the exhaust pipe.


LOLOL I really hope that isn't a quote from me!!!!

---------- Post added at 11:53 PM ---------- Previous post was at 11:40 PM ----------

http://www.nightrider.com/biketech/calc_exhaustlength.htm

For example this calculator wants longer overall pipes for lower RPM and shorter pipes for higher RPM (given the exhaust valve opens at the same time)

43* BBDC 3600 RPM - 58.8"
43* BBDC 4800 RPM - 44.1"
43* BBDC 6000 RPM - 35.3"

I think there's more to length as well. Getting into the harmonics of the wave in the tube.

---------- Post added 07-10-2017 at 12:01 AM ---------- Previous post was 07-09-2017 at 11:53 PM ----------

I kept the counter balance and the stock cam, stock carb. These are fine for engines spinning 5k or less. I'm using a 40 series TC which I was told worked fine up to 5K. The whole build was to stay at 5k RPM and under, so I got a 5k max RPM exhaust pipe.

The long pipe takes some of the area under the HP curve that would have been post peak HP and shifts it to fatten up the area under the curve before peak HP. That leaves the area under the curve post peak HP skinny and weak and frail. Hence the reason the power falls off so quickly after 5k RPMs with this long pipe.

 

[Denny]

In my experience the formulas for figuring pipe length and diameter never have worked out. They fail to account for things like valve size and flow, port work, carburetion flow, gear ratio and a whole host of other factors. Anyone who has drag raced and played with primary and collector length on headers will tell you the same. The engine will like what it likes and let you know. Trying to figure the exact length and diameter will drive you nuts if you let it.


Denny

 

[bob58o]

In my experience the formulas for figuring pipe length and diameter never have worked out. They fail to account for things like valve size and flow, port work, carburetion flow, gear ratio and a whole host of other factors. Anyone who has drag raced and played with primary and collector length on headers will tell you the same. The engine will like what it likes and let you know. Trying to figure the exact length and diameter will drive you nuts if you let it.


Denny

What if you're already nuts There's a lot of crazy people out there who have devoted there life to finding a single mathematical equation that solves everything.

Maybe FHB can run some tests with his DiYDyno?

 

[Hellion]

Ideally you want a straight pipe because curves are less efficient and have more resistance to flow... a curved pipe, if I understand correctly, is mainly a concession for compactness and space saving.

The whole shebang is an interesting topic no doubt, but there's no real concrete science as of yet--or is it that there's no perfect pipe?