The intake system should support the load-change. The higher the volume delivery, the more effective the load-change is. By delivery volume, the ratio of the real- to the theoretically possible filling of the cylinders is meant. A large amount of air means a higher oxygen portion in the filling. Apart from that, the oxygen portions, in slightly compressed air, have a higher density, thus, the combustion path is shorter.
A great help for a better filling was the introduction of the cross-flow cylinder head, in racing engines in the first- and standard engines in the second half of the last century. In this case, the in- and outlet are not on the same- (counter-flow head), but on different sides of the piston engine. The incoming fresh gasses can leave the combustion chamber in nearly the same direction again, and are no longer deflected. Thus the multi-valve technology, with optimum cross-section opening for the valves and the ideal central positioning of the spark plug (see above figure) is possible. Earlier, the counter-flow cylinder head had the advantage of more effective heating of the fuel mixture through the exhaust manifold lying directly below it. this advantage proved however, to be a disadvantage when the engine was hot. This is why the (later also thermostatically controlled) inlet air pre-heating has become rare. The only remaining disadvantage of the cross-flow head, the division of the engine in a warm exhaust-and a cold inlet side, must be compensated by construction and material choice. As one can see in the above figure, space is now created for a mighty, in this case, even adjustable vacuum pipe inlet system. In the meantime, it is made from aluminium or synthetics. Whereby, the synthetic material is heat resistant up to 140° and, compared with aluminium, weighs about one third less. Internally, the inlet system should be smooth and have no irregularities. The beginning of the air intake system and the cross-over to the air filter also require very careful construction. 08/06
Vacuum-pipe: approx. 50 - 200 m/s
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