[sammyg2]

Running 91 octane pump gas, he MIGHT be able to get away with 8 and 10.5 psig boost if his intercooler is over 90% efficient.

But he'd definately be pushing it.

I've turbocharged several engines, the latest were a 2 liter 914 and a 3 liter 911SC. Neither were inter-cooled but on pump premium the 914 was ok with 7 psig and the 911 could take a little more.
The SC was 9.3 to 1 and the 914 was around 8 to 1.

But why does he insist on 8 psig? Why not start low and gradually increase it until you find the sweet spot and then stop?

That's what I did.