Centifugal supercharger efficiency by restrictor

[vic52]

thread71-115031
LIMITING PRESSURE WHILE MAINTAINING EFFICIENCY of output of high capacity centrifical automotive supercharger by means of input restrictor as well as blow off valve.
Large Vortec V2 T trim centifugal SC used into high efficiency 3.5 litre 4valve BMW motor to rapidly raise boost to 7psi.
Dangerous side effect is potential 26psi at 55,000rpm needing to be reduced to 6 to 7psi by blow-off, with loss of efficency by excessive hp consumpsion & heat production.
Desire to limit input restrictor flow to 500 flywheel hp of air to give max efficiency at max hp, & limit air blow-off to upper midrange.
Are racing restrictor sizes any guide-eg 380hp with 35mm, with a big pressure drop?
Is the cross-section of SC intake to its max hp, with no pressure drop, a better guide?
It would all seem to depend on how well the Vortec sucks.

 

[gruntguru]

26 psi @ 55,000 rpm is a pressure ratio of (26+14.7)/14.7=2.76
To get 7 psi with the same PR would require an upstream pressure of (14.7+7)/2.76 = 7.8 psia. (This is your indication of how well the Vortech "sucks") Interestingly this is about the right pressure to achieve choked flow so your restrictor will only reach choked flow at peak hp.
Next, you need to size the restrictor to give the airflow you require for 500 hp (about 0.4 kg/s). A smooth 46mm venturi would be required. This assumes a less efficient engine than the 380hp from a 35mm venturi example (is this WRC?). That would equate to 500hp from a 40mm venturi. A supercharged engine will not make as much power as a turbocharged engine with the same size restrictor. Perhaps use 40mm as a starting point and machine it out till you get the boost you want.