The following compressor maps have boost & rpm line plotted on them to aid in comparing the stock SyTy turbo compressor to an "upgrade" unit. The blue lines roughly represent rpm of a 4.3 litre engine at 80% VE. I used the density table & pressure ratio formula from the Maclnes Turbochargers book.
Note the green dot showing 18 PSI at 5,000 RPM on the above maps. It is NOWHERE NEAR the peak efficiency (PE) island on the stock map. This may explain why I experienced little gain in drag strip performance when increasing the boost from 18 to 23 pounds.. The low efficiency levels are usually accompanied by excessive heating of the air charge, along with increased back pressure on the turbine side. Both of which kill power and increase the likelyhood of detonation. The 10 PSI line appears to cross the PE island from 3500 to 4000 RPM. Again, THIS IS ONLY AT 10 PSI! That's not a great deal of boost. The stock turbo looks GREAT if you limit your boost to 12-14 PSI. The Peak Efficiency island on the 'UPGRADE' compressor map reaches 18 PSI.
