There are several ways to control the boost of a supercharger too: bypass valves, bleed ports, drive clutches, variable speed drives, electronic controllers etc. You get the idea.
for example, from: http://www.clubsi.com/whats_hot.shtml
ZIP22 EBL (Electronic Boost Limiter): Exclusively engineered for use on JRSC equipped Honda/Acura vehicles with high boost pulleys. The EBL, Electronic Boost Limiter, is the first ever boost controller for a roots type Eaton supercharger developed by ECG electronics. It has allowed many enthusiasts to run high boost pulleys for the track and allow lower boost for street drivability & fuel economy without the need for swapping pulleys. The EBL has two methods of controlling boost, fully autonomous or user programmable (manual mode). The autonomous feature is a “set and forget” mode, which the user programs the amount of maximum boost; then the EBL will take care of the rest. The user programmable mode allows the user full control of the maximum boost attained through five distinct regions with respect to the throttle position sensor. The manual mode either extracts full linearity, or exponential production, of boost from the supercharger. Which is useful in autocross and drag racing events, respectively. The production of boost is faster than the mechanical actuator found on JR kits because the EBL boost control mechanism utilizes a sophisticated electronically controlled positioning system to moderate the programmed boost level precisely. The EBL not only controls boost, but also eliminates the dreaded tip-in detonation that is synonymous with roots type superchargers and also has a built-in VTEC controller. The EBL utilizes a 20MHz RISC processor, which samples a number of sensor parameters thousands of times per second for real time accuracy control of boost. A built-in 1 bar Motorola boost sensor, as equipped on J&S Ultras, is used to accurately measure boost pressures. The extra features found on the EBL are:
a) TPS mod: to help eliminate tip-in detonation
b) MAP mod: to richen/lean out fuel delivery (i.e. similar to the Apexi VAFC)
c) VTEC controller: adjustable VTEC engagement from 2500-5300rpms
d) IAT mod with intelligence: allows enrichment of fuel in the low and mid-range rpms but will cut-off at a user programmable rpm before the Honda ECU fuel dump to allow a perfect mixture across the motor’s rev range.
e) AF warning alert: audibly and visually warns the driver if the air and fuel mixture is getting to lean at WOT
f) VTEC light: this mountable LED informs the driver that the VTEC solenoid has begun to spool
g) Scramble boost: this feature allows maximum boost at press of a button
h) Valet feature: keep other drivers from tampering with your settings and allows no boost to be produced by the supercharger
The EBL has a handheld, mountable, user interface that has a built-in 16X2 backlit LCD display with large tactile buttons for easy menu selection. The LCD informs the user of real-time sensor outputs and the amount of boost produced. So if you want total control of your JR supercharged equipped Honda/Acura place an order for your own EBL today. Contact info: zipzoo_22@hotmail.com