If a valve is burnt or has a small crevace in it, you will lose compression and you will be able to hear it. If an intake valve it will push air back into the intake manifold. If its an exhaust it will be distinctly audible in the exhaust note. A burnt valve will show up more at idle than at speed, too. and if its a leaky exhaust valve it will make the car run a little hot.

oil in the cylinder can sometimes seal a leaking valve too.

Good luck.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.