2.8 pressure ratio means absolute pressure so 2.8 x 14.7 = 41, meaning absolute boost including barometric pressure. On a gauge it would read 26.5 psi.
Careful, wish it was that easy Josh.
PR=COP/CIP,
COP=plenum boost (MAP) plus plumbing losses (3 psi for us)
CIP=inlet pressure in absolute
A lot of people just use 14.x psia for CIP, and this is wrong. CIP must be determined experimentally. For an LLY, the plumbing losses are extravagant, 4-5 psi at stock levels, 8 psi at choke levels of airflow. This number gets subtracted from ambient pressure. If you are in Denver, ambient is 12 psia, and CIP=12-4=8 for stock flow, or 12-8=4 psi for 30 psi boost (42 psi MAP).
Now you can apply this to the compressor map, using a PR=COP/CIP=(30+12+3)/4=11.2...yes 11.2
that's in Denver.
Back near sea level, PR=(30+14.2+3)/(14.2-8)=7.5
The heat produced by the PR of 11, is a lot more than that produced at 7, hence altitude induced CAC overheating.:villagers:
These boost settings cannot be used for towing, for obvious reasons. A year ago, I condemned boost devices on the stock LLY because they don't discriminate. Until you can get rid of the inlet restriction, don't use boost higher than 28 psi, 24 psi at higher elevations, subjective opinion. These numbers still plot off the map, but they at least won't leave you stranded.
FWIW, even stock boost is off the map at elevation. And yes, this is the reason for LLY ECT control issues.
:bdh:
