+ // This magic formula yields about 4 inhg at 700 rpm
+ suction = pressure * rpm / (rpm + 4875.0);
+
+ // simple regulator model that clamps smoothly to about 5 inhg
+ // over a normal rpm range
+ double max = 5.39 - 1.0 / ( rpm * 0.00111 );
+ if ( suction < 0.0 ) suction = 0.0;
+ if ( suction > max ) suction = max;