Anyone have any write ups on how 4 into 1 work?

Dudes:

I know that discussions on exhaust systems are beat to death on this board, but I searched the net and did not come up with any answers to my questions.

From what I have read, performance headers reduce back pressure and provide a more direct route for the exhaust gasses to pass out. This reduced restriction creates a vaccume scavenging effect in the opposite firing cylinders that helps pull in more intake gasses and thus improves performance at high RPM's.

The benefits are the increased peak HP at high RPM's and a cooler sound.

The downside is a loss of low end torque and reduced fuel economy.

My question is: Other than reinstalling the stock system, How do you restore the low end torque after you have installed a 4 into 1 header? Do you have to rejet? Or would increasing the size of the baffel help to add back pressure to the system?

Problem is the bike runs fine and idles like a top 1200 - 1300 rpm's, but I have noticed that it does not start up as easily as it used to (have to give it a touch of throttle now, did not have to before) and it does not leave the line with as much grunt as it did with the stock system.

Anyone?

Yukabodos Buddy!!!
:blink:

You need to put your bike in your signiture so we know what bike you own.

Have you installed headers only or have you changed the filters?

Generally you need to check your plugs to see if your fuel mixture is too lean.

If your bike does not start as easily as before i would install a size bigger pilot jet. You probably need to go up on your main jet also.

This also should help out with your low end grunt. Roy

YUKABODOS wrote:

Dudes:

From what I have read, performance headers reduce back pressure and provide a more direct route for the exhaust gasses to pass out. This reduced restriction creates a vaccume scavenging effect in the opposite firing cylinders that helps pull in more intake gasses and thus improves performance at high RPM's.

It's a myth that reducing backpressure always leads to better performance. The intake and exhaust systems (as well as the valves/manifolds) are optimized to maximize airflow. That means you need the optimum exhaust backpressure, not necessarily the lowest. It is true that aftermarket headers (well designed ones) typically increase flow and up the HP (usually at the expense of low RPM torque). When the overall system is modified to increase flow through, it also means you have to rich the carbs/injectors to maintain proper fuel-air ratio.

One thing to remember, if backpressure is reduced and flow increased, the velocity may also be reduced (venturi principle) which may actually reduce performance. The trick is getting it just right.