Why is a high RPM engine better than a low RPM engine for performance?
It isn’t. Good towing performance usually comes at lower RPM. The big commercial trucks and heavy equipment almost always choose large displacement, low RPM deisel engines for best performance. The basic answer is essentially: the more fuel you burn per second, the more power you can get out of your engine. There are three typical ways to get more fuel per second into an engine: bigger displacement, higher pressure (turbo or supercharger) and higher RPM. Basically, if my engine sucks in one liter of fuel/air mixture per revolution and I want to (approximately) double my power output: I can run at twice the RPM; I can double the displacement at the same speed; or I can boost my intake pressure to 2 atmospheres. Or I could do some of each. You probably have to do significant engine redesign for any of these options. The reason that turbocharging and higher RPM are preferred for racing and aviation is that weight is a huge penalty in those applications. In big trucks, pumps, generators an
There are times when we wish that we could be better off running the steam engine rather than continueously improving the petrol engine. Now, for example is one of that time. Logical thinking might quick to assume that lower RPM usually translate to less fuel consumption. Part of it is true. With current automotive developments have opted to gained more horses out of screaming engine at plutonic RPM rates, we could reconsider the options. The automotive designer might reconsider the options to produce small engine with low RPM capabilities. Having longer stroke might help but the dimensions and design must be truly balance to obtain optimum engine flow. The top cylinder port design must be at the best calculative porpotionate to obtain maximum compression and flow. The biggest change might take form at the crank weight, shape and size. This is a must in order to preserve the torque but with small combustion bore and stroke, to improve or even match the RPM climb rate with the existing
