As chip said rod 8.4:1 isn't really a high CR, modern FI engines are using over 10:1 in some applications, made possible with good combustion chamber design and direct injection.

The higher the compression ratio the more vital timing and fueling becomes, a low compression ratio is much more forgiving at highish boost than a high cr...

IMO an mfi car is better suited to a slightly lower CR at over 20psi due to less accurate fuelling/timing etc.

My car is a bit over 8:1, if i were to build it again i would use stock CR if not slightly higher.

Rob,