Why are exhaust valves smaller than inlet valves?
The bigger one valve is the smaller the other has to be, the pressure expelling the exhaust gas is considerably higher than the force sucking in air through the inlet tract. Why are overhead camshafts better than OHV heads? Answer: They throw away several moving parts reducing frictional losses and allow much more accurate valve timing as the camshaft acts almost directly upon the valve. Why are 4-2-1 headers better for a road engine than 4-1s? Answer 4-1s supply more peak Bhp but at the cost of mid range power, which is what you need for a practical road engine. Also 4-1 headers are also almost impossible to fit to a right hand drive Spitfire because of the steering column. What is optimum exhaust back pressure? Answer = None! The reason most engines (except top fuel dragsters and the like) produce more power WITH an exhaust system is than believe it or not air has momentum. The air rushing down the exhaust manifold actually sort of `sucks` the last of the spent fuel out of the cylind
