[oil pan 4]

Well if you are running a really hot cam or have the cam timing retarded you get reversion back into the intake manifold, this reversion is what makes hot cams or heavily retarded cam timing make the engine run poorly at lower RPMs. So I would be surprised if adding a reed valve didn't work as advertised.
To be able to take advantage of a hot cam or retarded cam timing the engine has to be spinning faster than about 3,000rpm. Just having hydraulic lifters can tame the reversion on mid range cam grinds that have poor idle quality.