[steve25]

Sorry to hear of the issues your having Sam.

The main restriction in those heads is the stock valve job and the way the head bolt boss juts out from the common wall between both intake ports.

These heads typically flow less then 270 intake cfm out of the box and after a rework of the valve job go over 285 cfm.

Also as cast the roof In the runner of these heads are actually too tall for the as shipped stock size intake port gasket.

In other words they are made to have the intake ports use the RA4 / SD455 height gasket.

It’s good you have these on a 455 because this factor of overly tall intake ports effects around town drivability on motors of 400 cid or less, especially with rear gears of 3.42 or less.

These heads are also known to be shipped with too tight a valve stem clearance which can make a valve hang up, or ware the guide fast and then there goes your oil control and power .

NOTE that in each head two of the valve cover bolts holes break into the intake ports, so if your not applying sealer to the bolt or stud your using for the valve cover then oil can get sucked into the intake ports that way.

If your valve guides or valve stems are getting loose from the ware of being set up from day one in too tight a guide then no valve stem seal will do it’s job well when the rocking valve is making what was a nice round hole oval.