THe -4's have been used by some folks. 10:1 seems to be a good limit on the top end of the compression ratio. But running 10:1 takes into a lot of factors that have to be spot on to make the deal work. Jim Hand and Cliff have successfully used these type of slightly higher compressed engines. But neither post here any more. Maybe others can elaborate more.
I DO know that a tight quench distance is needed, no sharp edges in the chamber or on the piston, getting the correct cam and degreeing it is important, and of course the carb has to be spot on. There are more details needed, I can't think of any more at the moment.
THese higher compression engine details also apply to lower compression egnines, also...
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1977 Black Trans Am 180 HP Auto, essentially base model T/A.
I'm the original owner, purchased May 7, 1977.
Shut it off
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Buddy, I just shut your Prius down... 
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