Quote:
Originally Posted by FUNFER2
Question. Why does the FE like to have squared up intake & exhaust and lift numbers ?
Because the both valves are the same size ?
|
No, the valves aren't the same size.
Typical timing for many four stroke engines.
Makes it easy for the cam grinder, only one master needed to copy from.
The intake valve/s is/are nearly always larger than the exhaust on a naturally aspirated engine.
The intake valve has, at best, atmospheric pressure behind it, filling a negative pressure in the cylinder.
The exhaust is a high pressure (blowdown) as the valve opens, becoming near atmospheric at the end of exhaust, beginning of intake, overlap period.
Hence the "reversion" that occurs on the inlet stroke, seen in the inlet manifold runners on a plenum manifold, and part of the reason for the fuel cloud on IR carbs, Webers etc.
The longer the overlap period, the worse the phenomenon .
Gary