exhaust flow question: equation of exh. man., headers, pipes, mufflers,

[SeattleCharger]

Hello, my question is if the engine breathing affected by exhaust flow allowance is simply a measurement of the flow at end of tail pipe, in other words, the three main areas of possible restriction, the exh. manifolds, or headers, the pipe diameter, and mufflers, are in the equation, or to simplify, the exh. manifolds and mufflers.  What I am getting at is this:  say you have headers, but restrict the flow with mufflers when getting it quiet enough, or you have exh manifolds like hp exhuast manifolds and you use less restrictive mufflers, so that the exhaust flow at end of tail pipe is similar, is the engine performance the same?
   For example, if you had hp exh. manifolds and no mufflers (just for example), would the engine be breathing the same as if you had headers and regular mufflers?   The restriction overall is similar when all added up and measured at end of pipe, is this all that matters?   Hope this makes sense.   
  What is advantage of headers if you quiet them down with mufflers for street?   can't hp exh. manifolds be just as good if you have high flow mufflers?  or is it the point of breathing right at heads that is making some special performance advantage to engine?  if its restricted at the muffler point anyways, what does it matter if you have headers or hp exh. manifolds?   
 

[firefighter3931]

 
  What is advantage of headers if you quiet them down with mufflers for street?   can't hp exh. manifolds be just as good if you have high flow mufflers? 

This is a complicated subject but i'll give it a stab. Headers are better for cylinder scavenging. What that means is that the header, if properly sized will create a scavenging effect which is basicly a veturi/vacuum condition. This means that the engine breathes easier and the spent gases are pulled from the engine instead of having to be "pushed" out. The end result is less (exhaust) dilution on the next intake cycle...basicly cleaner air/fuel which will make more power.

The mufflers only function is to dampnen the noise and not create any restriction in the system. That is why flow thru mufflers make more power than a chambered muffler....all things being equal. Flowmasters are very restrictive by nature of their design. Mufflers don't have to be restrictive because the sound (volume) can be dampned more than one way.

Certain cam profiles will work better with a restrictive (manifold) exhaust system while others should be used with headers only. When choosing an exhaust system, it's important to look at all aspects of the build and vice versa when choosing engine components. 


As for exhaust sytem sizing, a good rule of thumb is :

2.25 for under 350hp
2.50 for 350-475hp
3.00 for 475hp and up



Ron