help I'm dum
 

Ok just got done putting a 350 mag together and dropped it in my old boat Im trying to sell (1983 nova XL) I wanted to make sure of all the wiring I did so I fired it up with no out drive or belts on her for a couple of seconds and noticed exhaust pulse coming from my thermostat housing (lower hose was off) so I pulled the hoses off the risers and felt exhaust pulse coming form both risers. I'm thinking the used manifolds I bought are cracked. Or exhaust pulse bouncing off the baffles in the tips and coming into the water jakets or am I really stoned right now?:grinser010:
thanks Dan