OK, I am not the smartest guy in the world. I hav had a problem with an engine I built for a guy and am not smart enough to figure it out. I was hoping for some input.
The engine is a lower hp $ copy of mine. It is a 468, stock type block, dart cast iron heads, ferrea valves, k1000 springs, comp stainelss rockers, and stud girdles. (my differences are 10-71 blower, jesel rockers (top end stuff) We run the same camshaft, lifters, springs, ret, keepers. So, damn near a low $ lower hp engine combo that I know works (for me I guess)
MINE, 7800 to 8g through the traps. 10-71, never adjust (ok, 2 x a year (stupid I know)) adjust the valves. Reliable as the day is long. 8.0 sec
HIS.. well, he says he has a 7200 rpm rev chip in in and he does not hit the chip, he says he runs 6800 to 7g though the traps. 9.0 sec
He had a new piece (he brought it because he had a lifter failure and tore up the cam) I frehsen up the piece. He jumped 2 exhaust pushrods out of the rockers this weekend. The lfters were fine, tight, etc. Second time, hit exh. valve and bent it. I thought he was adjusting valves worng, or something. Nope, I watched him. He did the same as I do. Maybe this, maybe that, etc.
I did check p to v. +.200 int and exh + lash
New guides, no exhaust seals, proper clearances (same as I have run and do run for years)
Pushrod lengths are right, patterns look beautiful.
Same cam, same/ similar lifters, same pushrods, same springs, ret. keepers, valves, heads, (not rockers)
Customer said the engine has had a history of some valve issues. Over hell, maybe 7 years I have done this engine maybe 2 or 3 times and he has had problems maybe 4 or 5 times in 7 years. So no big deal, but should not be happening.
The ONLY THING I can think of is spring harmonics in his opeating range? I never thought of this as a drag problem, really, more of a constant rpm issue?? I run more rpm, and flash through them quicker. He runs a direct drive, so it stays in an rpm range longer. I run 7800 he runs maybe 6800?
What do you think? I am missing something. Do harmonics set up at a certain rpm based upon spring, camshaft profile, or some of both?