Originally Posted by SSE 4 2SS
I understand one, I found an article, and went and read it...too much to post here, and I'm on my iPad, so it's hard to copy and paste, but I'll do so tomorrow when/if I make it put to the rig... Weather is sketchy...
there are tremendous amounts of variables, exhaust back pressure, cylinder fill efficiency, overlap, duration etc....
In a nut shell, as was just mentioned, it is an air pump, so, let it breath,,,
Good flowing exhaust, proper LSA, narrow in the boosted application, limit the duration, and wala, amazing power....
the exhaust can cause back pressure, which you want some, but if it reaches say 10 lbs of resistance, and you are pushing 7 lbs, and there is some overlap, both valves open at the same time, then the air will go to the point of least resistance... In this case the intake side,,,, with exhaust gases... If this is a 30 degree overlap in a 280 degree duration cam, then you end up with roughly a 85 percent efficiency in cylinder filling with fresh air...
The same can be said for velocities... Exhaust valves are smaller, and therefore the same volume, or actually more volume has to flow through a smaller are! So velocities are much higher... Leading to back pressure in a restrictive exhaust system...
If you free flow the exhaust, and limit the overlap via either duration and/or LSA, then you can achieve higher cylinder filling efficiencies with fresh air... And create more power.
Wow, now my head hurts...
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