Rusty,
So, it sounds like we've established my overall design specs :o))  As a rule of thumb 5 or 6 psi is more than I need and the engine will probably run all day with that level of boost in a cool environment with no problems.  That's what I was looking for all along - something the engine could live with very easily, would not require extensive intercooling and would turbo normalize to just below 18k ft.

STILL ... just a theory .... Jim S.

PS  On a 60 F day, the OAT at 16k ft is about 12 F; on an 80 F day, the OAT is maybe 32 F
 

Russell Duffy wrote:

 On a 60 F day, the OAT at 16k ft is about 22 F; on an 80 F day, the OAT is maybe 42 F.  These temps would tend to reduce intercool requirements and cool the turbine which I assume (key word here) is the reason for limiting boost to 8 psi. 8 psi is a rough figure that I came up with after searching through some RX-7 forum info.  This seems like a reasonable value that folks are running on the street.  Since that's already more than I need, I didn't look further to see why they don't go higher.  It may not be a turbo limit, so much as a limit to the engine computer, or fuel injectors.  For example, on the 3rd gen engine, you can run aftermarket exhaust and intake with the stock 10 psi boost level using the stock computer.  If you want more boost, you have to install an aftermarket computer.  This will get you to about 13 psi, then you run out of fuel injector capacity.  Next you run out of fuel pump capacity, etc.   The stock twin turbos can be run to about 17 psi, but this is way above their efficient range, which means they're heating the air much more than a larger turbo would do at that same pressure.  In that respect, running higher than normal boost for a given turbo will increase the need for intercooling. Rusty

--
Jim Sower
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T