most are set on gate pressure you can add an electronic boost controller but the stock ecu ( usually used on low boost setups) has no facility for boost control. Low boost on a totally stock engine is around 220-240bhp at around 8psi, though with a meg headgasket you can run a max of 12psi circa 280bhp.
I loved my last low boost 172, added a huge chunk of torque but it still liked to rev, really picked up its heels. I sold my kit for about 1200ish i think maybe 3 years ago.