Need some info. Ok, four valves per cylinder is better than two valves per cylinder. Fine, why did Ford REVERT to only 3 valves (my guess is to save cost SOHC)? Audi and VW are using five valves per cylinder on some cars, does this offer any advantage over a four valve engine? Maserati even experimented with a six valve per cylinder!!!! (see link) http://www.maserati-alfieri .uk/alfieri26.htm but abandoned it (my guess is cost again?) Why are we stuck at four valves or would more valves actually render more horsepower? Pop some ideas best answer to reasonable answer...
There are multitudes of problems to resolve and strike a balance... ...In a zero valve, 2 cycle operation , clearing the cylinder of exhaust and recharge it is as basic as it comes..... ...In valved, 4 cycle operation, one valve each for exh and intake, has the least add-on linkages/cams , but limits the speed and completeness of clearing the exhaust and fully recharging the intake. By adding additional valving, the rapid removal of exhaust and recharging is accomplished, at great expense for add-on linkages/cams etc, and great loss of power...since you have many more items to accelerate and decelerate. The ideal valving, is to effectively remove the cylinder head for exhausting, and replace it for charging, but it would be a mechanical nightmare......therefore, compromises are made...2, 3, 4,6,....total head ???cost.. st...vs performance.
The ideal situation would be to remove the head during the intake stroke and put it back on during the compression stroke, but, obviously, this isn't possible. On a naturally aspirated engine, the intake is the most critical because the air is moved only by a relatively small difference in pressures. The exhaust stroke, on the other hand, is aided greatly by the super heated temperature and rapid expansion of the gasses.
One advantage is that of pressure differentials. For the intake of a non-aspirated engine, not supercharger, the pressure differential between the atmosphere and the cylinder is about 14.6 lbs. maximum, atmospheric pressure. For the exhaust there is a high pressure in the cylinder and therefore it is easier to clear out most of the burned fuel mixture. So exhausting the cylinder is easier than getting the fuel-air mixture into the cylinder. It is a bit simpler to make one large exhaust valve and two smaller intake valves as far as the layout of the valves in the cylinder head. You save on parts is one consideration. Also, high revving engines make more horsepower but passenger cars never see the advantage of higher horsepower like racing engines do. If you build racing engines, it is not that difficult to use the same cylinder heads or last years heads. If you don't build racing engines, you are not worried about high horsepower designs and more about keeping the cost of the engine reasonable. You probably never use all the horsepower your engine is capable of delivering so why pay for more engine than you will ever use?
