I know, that an exhaust header increases hp. But i could not explain why. There are exhaust headers with different tube legnth. Long Tube = power at high RPMs?
But a long Intake manifold makes power at low RPM, a short at high. Inverse to the exhaust header? why?

Knows somebody a link where the funtion of a exhaust manifold is illustrated?

 

http://www.burnsstainless.com/....html

They provide the name of a book at the bottom of the page for more basic exhaust theory.

 

Thanks,
Anyone else?

 

I wanna keep this short. to understand why header works you have to understand the motor itself. you have 4 strokes:

Intake stroke: sucks in Air, and fuel gets sprayed in at the same time. (piston goes down)

Compression stroke : the air and fuel now gets squished up against the head (piston goes up)

combustion stroke: spark plug sparks and ignites the compressed fuel and air (piston goes down)

exhaust stroke: the burnt up air and fuel turned into smoke and the piston needs to go back up and push it all out thru the valve and out the head into the headers and down into the exhaust and out the back of your car..

now if your headers are small, not all of the burnt up exhaust gets to escape on the exhaust stroke, so when the engine is back on teh intake stroke it cant hold as much air because there is still a small percentage of exhaust gas in the chamber.

now with bigger headers, it helps release more exhaust on the exhaust stroke, so when you are back on the intake stroke you can fill up the chamber with more air and fuel for even more power. your headers are like the neck of a pepsi bottle. if you uncap the bottle and turn it upside down it takes a good 30 seconds for all the soda to come out completly, because the neck is so slim. and the volume of soda is so great. but if you chopped of the neck and turned it upside down it would take less than 8 seconds to pour it all out. thats how bigger headers are like.

in a nutshell, bigger headers allow more exhaust to leave per exhaust stroke. giving more room for fresh air and fuel per intake stroke.

 

Also the pressure wave from the exhaust leaving the cylinder and going down the header pipe will create a vacuum and pull the exhaust out of the next cylinder when its on its exhaust stroke and so on..

The 4-2-1 headers have shorter runners so they will "pull" better at lower rpms and the 4-1 will "pull" better at higher rpms..