Valvetrain noises

[Jmand]

Back again with (probably) another dumb question! So I got the electrical bugs out of her ('73 'cuda 340) and now I'm noticing a "clacking" under hard acceleration, say 3800 rpm plus. Fear gripped me but I drove her for another twenty minutes and it was all fine unless I really stood on it. First thoughts were lifters? Did the old test, ran her in the driveway at "clacking" rpm for a few and checked each header tube - all hot (very hot   ONly other thought without tearing into her is a header leak. Guy i got the car from had lowered  ( 3 leafs out back) and just pulling out of the driveway I've dented my driver side headers all up. Dying to drive her now that nice weathers returned to the city - any advice or test I can run??
Thanks!

[Chryco Psycho]

probablyt a header / exhaust leak

[Bullitt-]

could it be pre-detonation? a bit high on the RPM but clacking is exactly how I would describe the sound. 

[Oldschool]

Could be either of the above, and both are easy to diagnose and repair.  Hope it is something easy and cheap to fix!       

[ShelbyDogg]

I agree wit Bullitt, It's probably pinging. Try retarding the timing a feww degrees and see if it gets better.  By the time you can hear it, it's too late.

Rob