I have an issue with the whole backpressure thing. Backpressure is bad. period. Take the fastest cars..top fuel dragsters...they run short,open pipes (I know, they have superchargers)
However, a system needs exhaust pulse control which is good, as shown in well designed headers.
We want good flow to get a fresh charge of air into the cylinder and exhust gas out of the cylinder with as little wasted fuel as possible and maintaining stoich. This new A/F charge whould be at the optimal A/F ratio.
So:
1) DECREASE exhaust back pressure equals better flow....
2) Incoming charge pressure has to be greater than exiting charge pressure..
3) flow is in the direction of decreased pressure, so that exhaust flows out of cylinder BEFORE upward stroke and at early upstroke (see 6)
4) Smaller pipe, higher velocity =lower pressure (to a point)...but inabity to flow higher volumes
5) Larger pipe, lower velocity=higher pressure(to a point)...but better volume flow
6) Valve overlap so get the gasses flowing the right way
7) Laminar flow is best
8) Exhaust pulse problems and interference changing exhaust pressure
9) Intake and exhaust design go hand in hand
10) NO way any one exhaust design is best at all rpm's
Therefore: Pick where you want your power.....in other words:
all rpm range street driving...standard exhaust and intake system very good
Racing with generally high rpm's...Bigger exhaust, less restriction, AND different intake design
Or, you need a 'variable' diameter/length exhaust which changes with volume/temp...etc
Or, an exhaust with an expansion chamber design up front and a condensing design towards the rear increasing flow at both ends of the exhaust...
Of course, with modern aftermarket electronic A/F control...you can tune the mixture to correct ratio at any air volume/ rpm range
Much to think about before cutting anything. Consider some of the proven systems already on the market...
