If a 1986 350 El Camino with a performance cam has low vac to booster 8-inch vac has no brakes what do you do?

the only thing to do is replace your cam with a lower duration cam or you can try adding a brake booster resevior to store vacuum for the power booster. == With such low vacuum, you might want to add an electric vacuum booster pump to augment the vacuum booster resevoir.