Why does everyone get 2-1 exhaust?
Outstanding HDF Member
Joined: Apr 2012
Posts: 2,938
Likes: 30
From: North Florida
With big old fat pipes the flow gets lazy. With two into one the scavenging of one pipe causes a slight vacuum in the head pipe so when the valve open the head pipe has a slight vacuum so the gas does not have to push its way out of the cylinder.
Seasoned HDF Member
Joined: Mar 2007
Posts: 66,948
Likes: 4,573
From: TOAK western branch
Well the main reason people call for the need for back pressure is lack of velocity and scavenging.
With big old fat pipes the flow gets lazy. With two into one the scavenging of one pipe causes a slight vacuum in the head pipe so when the valve open the head pipe has a slight vacuum so the gas does not have to push its way out of the cylinder.
With big old fat pipes the flow gets lazy. With two into one the scavenging of one pipe causes a slight vacuum in the head pipe so when the valve open the head pipe has a slight vacuum so the gas does not have to push its way out of the cylinder.
Road Master
Joined: Nov 2009
Posts: 1,218
Likes: 0
From: Yakima WA
I run 2 into 1 pipes on both of my bikes because I don't want to leave any horsepower or torque on the table like 2 into 2 pipes do. The improved scavenging of the 2 into 1 just does a better job at producing good numbers.
Ultimate HDF Member
Joined: Apr 2010
Posts: 7,138
Likes: 26
From: Southern Oregon
One purpose of a exhaust system is to provide a means for the exhaust gases to be removed from the cylinder, preferably quickly and completely. The term for that is scavenging. Back pressure is a term for resistance (obstruction of flow). A cylinder with residual exhaust gases has less room available to accommodate the incoming charge of gas and oxygen. Obviously, the more gas and oxygen you can get into a cylinder the more power you will achieve. Scavenging not only helps empty the cylinder, it also helps drawing in the new charge by producing a negative pressure. Unless a 2:1 system has a crossover pipe one cylinder does not help the other in scavenging like it does in a 2:2 system.
This is very basic, there are a lot of other factors that come into play (valve timing, rpm, wave length, pipe length, diameter etc...)
This is very basic, there are a lot of other factors that come into play (valve timing, rpm, wave length, pipe length, diameter etc...)
Road Master
Joined: Dec 2009
Posts: 1,118
Likes: 5
From: Coweta, Oklahoma
I saw the two into one Vance and Hines big radius on a bike at HD yesterday on the showroom floor and it looked nice, but I prefer the two into two myself.
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Tourer
Joined: Dec 2010
Posts: 250
Likes: 0
From: Mesa arizona
I am with you I hate the look of two into one pipes. I also hate the all of the pipe that 99% of people put on there touring bikes. I think I am the only one in Arizona with bir radius 2 into 2 pipes on a full dresser