[Rick Parker]

The manifold mismatch will not have any affect on leakdown %'s. Leaking valve seats (hissing heard through carb) or rings (hissing heard through breather/valvecover opening) are the tell tale signs of potential problem. Pressurize from a source at 100 PSI through spark plug opening and read the pressure on secondary pressure gauge. The difference between the two gauges is interpreted as your loss in %. It has nothing to do with what the compresssion ratio is, only the condition of valves and rings. The test assumes head gasket is uncompromised. Do it on a thoroughly warm engine. Do one bank, then rewarm the engine for the other side. 2% - 5% or less is target.