RPM reading

[Tony]

Have a look at the waveform directly across the SCR with your oscilloscope.
It should be negative going, and look exactly like the small blue drawing on the circuit diagram. It will be quite narrow, but must be very clean, and pulse only once at regular intervals, and only pulse when the spark plug fires.

Then check the waveform coming out of the 555 timer. It should be positive going, with very fast vertical rise and fall, but much wider than the SCR pulse. Quite likely your counter only responds to the negative falling edges, so I doubt if that is the problem.

Not sure there is a recognised standard ramp rate for rolling road dynos.
I believe 600 rpm/sec is a fairly commonly used ramp rate for engine dynos.

Before you can ramp a rolling road, it must be able to hold constant speed against very sudden throttle openings and closings. Only when the dyno closed loop speed control system is working really well, can you feed a rising speed command ramp into it, and have the dyno respond appropriately.

Unless the dyno speed control loop responds very fast and very accurately, the ramp rate will wobble around, and the ramp rate will change as engine torque changes.