it seems every time i try and calculate this i get in a muddle some where , just dont know where ?

take example - target 400whp , purely hypothetical , i know the engine cant take it but its a nice round figure worthy of twins to work with,

-- first off figured that a capacity of 116ci with a VE of 85% say at 4000rpm , ambient temp 85f , AFR 17 , BSFC 0.365 say - Requires 41 lb min at a PR of 5 ( 71 psi absolute )

-- Next sized the secondary - not much effort, say - vnt20 at 4000rpm makes 22lb min ( half total flow ) @ 2.7 P.R ( almost half total pressure ) at 65% compressor efficiency

--- Now as i have the vnt20's P.R of 2.7 , i thought i should be looking to size a primary to include a P.R of 2.3 and 40 lbs min - 2.7 + 2.3 * 14.7 = 73.5 absolute ( required for 400whp )

but im not sure thats relevant as its not figured for density .

-- So with intercooling between stages ( WI would be better i know )

unknown primary as yet but - inlet temp 85f - inlet psi 14.7 - output pressure 2.3 P.R 34psi absolute - targeted compressor efficiency say 70%

= an output temp of 399f - P.R 3.31 - density ratio 2.1

-- when put through first stage of intercooling which is 80% efficient - 1 psi loss - 80f outside temp

= Outlet temp 144f - P.R 3.24 - density 2.93

-- Now with 144f output temp + 34psia plugged through density calculations once again but for the VNT20 but with 144f as inlet temp - inlet psi 47.6 absolute 3.24 P.R - 65% compressor efficiency - output pressure 73.5 psi absolute P.R 5

= Outlet temp 425f - P.R 2.54 - density ratio 1.74

-- After 2nd stage of intercooling ( same efficiencies as the 1st )

= Overall Outlet temp 149f - Overall P.R 2.52 - Overall density ratio 2.51

-- With the engine being in normally aspirated form the calculations with capacity , VE , and rpm being unchanged at - 116ci , 85% , 4000rpm , show the engine to consume 12.82lbs min before boost

-- so when applied with the overall density ratio from above which equates with the overall required P.R from both stages 73.5 psi absolute

12.82 * 2.51 = 32lbs min - suggesting that, that is the primary flow to be sized ?

which seems to have lost me completely 32lbs min ? , if any one can put me back in line , i'd be hugely grateful , pull apart at will !

( ive been on a wing an a prayer from the very start to be honest )

cheers especially tdimeister

- though despite your best efforts + valued Patience my meatloaf still appears to be letting me down