You will likely get a variety of responses ranging from 10:1 is fine to throw as much compression at it as you can. I know because I asked a similar question last year.
As a result (and further research) I am taking my 358 SBF from 11.2:1 to 13:1 as part of my changeover from Enderle (hat) injected gas to alky.
But this could be only a part of the solution. What types of problems is your buddy having?
Murff