There would have to be a standard of measurement for any data to be useful which there is not. Distance, environment, and placement of microphone all would have a dramatic affect on SPL (loudness) figures. You would also have to specify what scale it is to me measured in (A weighting, C, or flat) besides a constant engine rpm.
BTW, a 3 dB SPL increase is NOT twice the volume. This is a common misunderstanding of decibel measurements. It takes twice the power (watts) to increase the dB SPL 3 dB (speaker measurement) which is not twice as loud.
