Valvetrain sound after 2000 rpm.

Hi all, I have a bit of a mystery on my hands.
I have gotten my 65 Mustang out of its 8 year slumber. The car has a 250 with a T5, DUI ignition, a 2150 carb on a 2 to 1 plate.
The problem is that the engine makes alot of valve train clatter noise above 2000 rpm. I have checked the compression in all the cylinders and they are all 155, give or take 5. I checked the oil pressure and it is 25ish at idle, but goes up to 50ish under throttle.
What is interesting is that the valvetrain noise is worse under light load, but under heavier load I can get the engine up to about 3500rpm without hearing much valvetrain clatter. I have played around with changing oil, trying additives like Marvel Mystery oil or seafoam just in case it was a collapsed lifter, but nothing seems to make much difference.

Anybody have any idea what this could be or what to try?

Pull the valve cover & see if the rocker arm shaft is getting plenty of oil?? Good luck.

... sloppy cam chain slapping around ? , tightening up at higher RPM ?. ... rock crank FW / BW with plugs out - listen and see how distrib or PR's move.

Howdy Back Yoda and All:

Since the engine has been modified, I'd add to Bill's advice to remove the valve cover to check for sufficient oil- and also to check on the condition of the rocker arms and the ball ends of the push rods for excessive wear. Does this engine have adjustable or non-adjustable rocker arm. IF non-adjustable check valve clearances. If adjustable check clearances and re-ajust as needed for your engine, which I assume has hydraulic lifters- so zero clearances.

IF the engine has been sitting dormant for 8 years I would strongly suggest that the inside of the rocker shaft is due for a good cleaning. The inside of the rocker shaft is a transfer tube to get oil from the back of the engine to all of the rocker arms, with the front ones getting oil last, on start up. They are also the ones to show most wear.

High detergent oils are good for cleaning the inside of the oiling system but they may not be enough to clear blockages, and work slowly over time.

How old is the engine? How Many miles? compression sounds good but may not be the complete answer on component wear. PBs suggestion on checking for timing chain wear is a good one. The only solution there is to replace the cam timing set.

Sounds like a great ride. So keep the info coming on both your ride and your progress.

Adios, David

Hi, I would run it with out the valve cover and make sure there is good oil flow to each rocker arm. The rocker arms have squirt holes which can become clogged. Good luck

You've got to pull the cover. How many miles are on it? How did it run when parked? Are the rocker arms adjustable? If they are, adjust them or replace the rocker assembly with a stock non adjustable rocker assembly and let them adjust themselves so long as you aren't running a hydraulic cam and lifters.