With the major components in place, it was time resolve the vacuum system problems related to boost in the intake system. Four circuits that relied on vacuum were modified with check valves to prevent internal or external problems from boost pressure. They include the crankcase vent at the F.I. plenum, the power-brake booster, the distributor vacuum advance, and the fuel bowl vent into the F.I. plenum. Each line was fitted with a check valve from Smart Products, Inc. in San Jose, CA.