I don't get the 9.0:1 Street Hemi idea - the chamber is not that sensitive to octane.
That's a fundamental reason Chrysler introduced it for the '51 models.
I ran 10.8:1 in mine with iron heads on Calif 91 and it never rattled.
Granted, the cam had some overlap that bled off a bit of CR, but it had a fairly aggressive curve, 36 total, + vac advance.
I don't get it either but then again the engineers at Chrysler thought it was a great idea to make the stage 6 wedge heads with a raised intake port entrance and stock iron wedge head valve lengths ...
