RPM. What is Best?

Here are the torque curves for a unmodified 2100cc water boxer, and all of the larger GoWesty engine variants:


The peak efficiency of any engine occurs at the RPM where it makes peak torque. Peak efficiency means highest power output with the least amount of fuel and wear. You will notice that peak torque of all the engines we offer, regardless of size, occurs right around 3000 rpm. It is no wonder that is where VW put the tach needle straight up and down, smack dab in the middle of the green zone!

Indeed, even our largest, most powerful engine make a lot more torque, and for a much wider RMP range—but its peak is right about the same spot! This is due to the fact that the fundamental, overall design of the engine is the same for all the variants we offer.

The other side of the coin is HP, which occurs at a much higher RPM:


Here again, you see that the peak HP occurs at around the same spot for all engines, but not at the same RPM as peak torque. If you were superimpose the T and HP graphs, you would see that they intersect somewhere between 3000 and 4000 RPMs. It is at that point where you feel the “sweet spot” which, anybody that has spent any time driving a waterboxer-equipped Vanagon knows, is around 3500-4000. This is indeed true for any all of our larger variants included.

So, what is the right RPM for any particular situation? It all depends on how hard you are working the engine, and how much of a hurry you are in! Here are the rule of thumbs:

Really slow: If you are cruising around town at part throttle, or even light throttle-the lower the RPM, the better. You can’t really go too low. If you look at the graph, you can see that even a stock 2.1 make 30+ HP 1500 rpm. Poking around town at 30MPH, all you need is about 30HP, so why not?

Highway: Cruising down the highway at steady state for long, long periods of time—the closer you can stay within the sweet spot, the better.

Hard work: When climbing a steep grade, for example, you can down shift, back off the throttle and cruise on up at around the sweet spot. What gear you are in, and how fast you go up the hill, all depends on how powerful your water boxer is. Regardless, the fastest way to the top  with any engine, is to wind it up to around peak HP. But just like anything, there is no free lunch! When you ask a machine to make more power, you are asking it to perform at a higher duty-cycle, which necessarily reduces its expected life. Plus, you use quite a bit more fuel.

Patience is a virtue and, like my dad used to say, “Go slow, get there faster!” (except in Spanish.)