At the risk of getting "Sniped". I just helped a friend on his small block Chevy that was sucking the lower hose shut whenever you opened up the throttle. Everything is new, not rebuilt, the cooling system flows like a mother. We ended up installing a spring in the lower hose. It helps keep the hose from collapsing, but you can still see it getting sucked in. I would be interested in knowing what the causes of this are and what possible fixes could be employed. (Don't say thermostat, we changed it and nothing was different.)
Revhendo