Get it up to a speed where the transmission takes a hard jab to kick down to second gear and roll into the throttle. You'll feel how the boost comes in. It's interesting to feel your rate of acceleration, well, accelerate as boost builds.

The hot rod was about as tight as reasonable on a street car. About 1/4" of throttle at 60 mph in 3rd gear would build boost and I'd be close to 90 mph by the time I got around the truck I was passing.

You can also lock it down in 1st gear and see where the boost builds. That's a bit deceiving because the gear multiplication doesn't load the engine as hard and it revs easily.
When doing that, the hot rod would start making boost by 2800 rpm and the car would be sideways by 3200 rpm.