Essentially Phil, its like this.


Take an example engine (yours if you like)

Take a point in the rev range, ie 4000rpm
and a particular boost figure ie 32psi of boost



run those numbers on the samge engine at every CR:

7.0
7.1
7.2
....
11.9
12.0


For a particular fuel, and then map it on the dyno for each CR


you will find an OPTIMUM CR for that particular circumstance.


Then do the same again 4500rpm, 5000rpm, 5500rpm


You will see that for each successive rpm increment you find that optimum figure moves higher and higher up the CR chart.


If you want you can then plot that as a graph

You will then have a curve of CR against Torque at each point in the rev range on the boost and fuel you are choosing to use.


You then decide from that curve which CR you want to maximise the power of the engine at the RPM you want it, it will be a compromise for every point in the rev range except one, by definition.




Ive slightly over simplified things there, ive ignored cams and their effects on VE through the range when ive said higher rpm = higher cr, for any given engien there will be some small parts of the rev range where that isnt true.

But with the level of detail its practical to go into in a post like this, what ive said holds water pretty well.