A dyno test is where you lash the car unto rollers that are connected to a Dynamometer. It measures RPM and torque at the rear wheels. You are actually driving the car "in place". Usually a computer gives you a printout and a read-out on a screen showing torque, HP and speed, sometimes fuel mixture. You can load the engine that way and adjust timing to suit. There are also places that advertise having a dyno, but it is only a drum your tires accelerate as you step on the pedal and it shuts off when you reach redline. It also gives HP but does not provide a steady state loading. It is less desirable for making adjustments, although it serves for comparison. Cost varies, I have seen it for free to $145 per run. I have played with timing. The start of pinging depends on the octane of fuel. I use regular and my timing is set to the book, i.e. 30º at 3000 and about 3º after TDC at idle. Engine runs really very sweet that way. Dyno indicated 156 HP. Keep in mind this never was a hot rod, but a touring car.
'69 280SL,Signal Red,113044-12-007537,tired engineer, West-Seattle,WA