Re: Which manifold for 4.3 Vortec/OMC?
The 4.3L Vortec engines are really bad about sucking water back into the exhaust. Even worse than a V8 Vortec.
OMC and Volvo both used a 2 piece riser and manifold on the 94 and newer V6's (Not sure about earlier OMC) and in 94 Volvo and OMC went into the joint venture.
Anyway, they also have a special elbow that prevents water from sucking back into the engine. (Item 18 in the pic below)