Ways to increase engine speeds

Is there any way to increase the speeds of HO (any gauge, really...) engines via the transformer? Is bigger faster? Is more expensive faster?

Re-gearing is the only way to go, although I must admit, most folks are trying to figure out how to scale DOWN the speeds of their locos, into a more realistic range. Higher voltage would work, for a few, brief moments, but then you will experience failure of the motor, due to overheating, shorting or burning through the rather thin wires, not intended to carry higher volts/amps. More expensive doesn't mean faster. You want to know the variable output maximum, for train speed control, as well as maximum amps, and minimum continuous amperage output. This generally, is not effected, by price. How "clean", the electrical signal/output, and the amout of "steps" between zero, and maximum output/amps, may be affected, by price. Another possibility, is to re-motor, with a higher speed motor, of the same general size, and voltage/amperage requirements. A motor turning 10,000 rpm will obviously move your loco faster, than one with a 5,000 rpm max speed, assuming both run off of 12-14 volts, at perhaps a 3-5 amp max load ? Good Luck ???

Well, a bigger controller might be faster if you're running several locomotives. A simple trainset controller won't be able to power 4 locomotives at a very high speed, while a more powerful controller (such as an MRC Tech II or Tech 4 with a single throttle) may be able to power a dozen locomotives at a decent speed. Some power packs will only put out about 10 V or so, in which case increasing to a larger power pack with a 12-14V rating would increase the speed without (hopefully) burning out the motor.

However, in my experience, I rarely ever use more than half the available power. An Athearn locomotive by itself will run more than a scale 100 mph on a typical controller, far faster than freight locomotives will ever run in real life. As mentioned before, any faster than that and you'd want to change the gearing or upgrade to a faster motor (neither of which I've done). Keep in mind that higher gearing would adversely affect the locomotive's slow-speed performance.