Consider a pd300 making 200hp @30kft where,
2.1lt is 128 cubic inch
@30kf ft o2 density is 1/3 of sea level which means turbo has to push around 60lb/min air
Bsfc is around 0,55
Assume VE around %100 at sea level around 3000 and 4000 rpm
Then
Without a turbo engine power would be,
0,55x128x1(VE)x4000rpm /1728
:162,96cfm /14,472 = 11,26 lb/min at atmosperic pressure mean 113hp
Now pressure ratio has to be around 5.3 which is around 4.3 bars. I just realised that for 2.1l engine there is not any turbo that can provide that power in displacement.
Consider given turbocharger below, it is only capable of pushing 3.6 bar(believe me a turbo with exceeding that level will affet spool performance quite adversely), then
11,26lb/min x 4,6 (pr) = 51.8 lb/min which means 1/3 of it at 30kft means 172hp is around maximum possible given bsfc is 0,55 and VE is %100.