boost pressure in a parallel twincharged setup


Full member
mitsubishi evo 9
Looking to combine rotrex and turbo [theory only atm] with siamesed intercooler intakes running simultaneously and not feeding into each other [?avoiding retrograde flow with valves]. I imagine flow is added from each but is pressure also added together i.e. at 'x rpm' if turbo is making 10 psi and rotrex also on 10 psi, what is the combined pressure ?
As I understand it, the parallel setup is additive (10psi +10psi), the sequential is geometric (1 bar into 1 bar yields 4 bar).
As I understand it, the parallel setup is additive (10psi +10psi), the sequential is geometric (1 bar into 1 bar yields 4 bar).
Thanks yldo :) recently dug up a few subaru wrxs with twin screw and centrifugals but critical info re piping and boost management lacking. I will do a full write up if/ when I get there.
Here is a practical example of how this works:
S/C boost =5psi
T/C boost =32psi
inline calc: (boost+atmosphere-loss)/atmosphere = 54psi
adjacent calc: (boost+atmosphere-loss)/atmosphere = 50psi

inline pressure ratios (1.24x3)
adjacent pressure ratios (5+32+14.7-1.5)/14.7
Adjacent = parallel setup?
5+32+14.7=51.7/14.7=3.5 is pressure ratio? Or 2.5 bar, correct?
Yes, the pressure ratio is multiplied inline and summed when adjacently (parallel/common) piped. In my instance, I lose 1.5psi through my air filter, manifold restriction, etc. Take those into account and your numbers match mine.
Are you hapoy to share build spec, boost curve/ piping, dyno and broad mapping strategies? An expert builder and expert mapper will be doing all this but I want to know as much as my little brain can handke as I am driving the project to be and funding of course. Only this am came across garage g (japan) evo x hks centrifugal and turbo. Learning more every day. I plan on kickstarting project @ October . Cant register on eng-tips as I am no engineer.
Let’s look at one last real world example to nail it down for all reading:

S/C = 8 psi
T/C = 24 psi
atmosphere = 14.7 psi

adjacent feed calculation: (8+24+14.7-1.5)/14.7 = 3.0 pressure ratio and 44.1 psi @ 14.7 psi ambient
inline feed calculation: (8+14.7-1.5)/14.7 x (24+14.7-1.5)/14.7 = 3.64 P.R and 53.5 psi @ ambient

You’ll note that for a given inline total boost, the disparity in final boost increases as the boost levels of the two chargers equalize. The best analogy for this is the area measurement of a rectangle. The perimeters of a 2 x 6” and 4 x 4” rectangle are equal but note the area difference. The numbers above are NOT temperature corrected so the actual boost will be quite a bit lower if you don’t mind the inter-cooling. I'll be providing information in my other thread on this topic. I hope you understand why I can’t provide those calcs for free 8^)
Hi I am new to this page but this is exactly why I joined. I am doing this at the moment on a RB30.
My biggest question is what why to plum it all together. I wanted the supercharger feeding into the turbo because it would save it if the turbo let go but not sure how well that will work. I'll keep reading the posts before making that decision. Cheers

Similar threads

Please watch this on my YouTube channel & Subscribe.