[vintovka]

Thanks, What i was thinking. Pump kit is standard one with pressure switch (18-22") and will add check valve between manifold and line. Check valve at booster will remain. You described exactly what is happening even with 18" at idle or coast. While theres a little info around on piping options (like connecting pump "exhaust" to manifold vacuum). The low vacuum problem seems like a very common issue and a pump or HB seem the common solutions. Pump makers and users, however, seem hesitant to share info. Those who use the pump seem to like the results but complain mostly about the noise. May move or enclose the pump if it works. Being a somewhat anal retentive engineer I installed a shut off switch so i can compare braking with or without the pump. Had I the funds/ resources i would have used a diesel engine with the HB systems they require. If circumstances allow i'll report back on how it went and maybe offer a diagram.