high rpm "popping" sound

Squash mpc at genevaonline.com
Mon Apr 6 19:13:47 GMT 1998


I was out 4-wheeling (yup, in the mud) sunday and noticed something. 
This is my first high-rpm run with this truck/motor.  4500-5000 rpm, 454
with holley projection, 268 cam, headers, alum intake, etc.  It sounded
like an ignition miss.  I have a new accell blueprint HEI (electronic
advance) with all new accell parts except the coil, which is probably
100 years old.  Also running 34 degrees total ignition advance.  I
recorded a run on the laptop, and analyzed it.  I could not see much of
a pattern except that it only occurs over 4500 rpm.  The O2 almost the
entire time was around 60 mV.  Normal cruising usually reads around 85
mV.  Here's the question(s):

Will the O2 read correctly under very heavy throttle (50% and up), and
if so, does 60mV sound lean, and could my popping sound be from running
lean?

Could this be my ignition?  The only original part is the HEI coil.  The
spark plugs are brand new and gapped according to the manual (can't
remember what, tho).

And lastly, could this be valve float?  I know that big-block chevrolets
are known to do this, but i have never experienced it, so i don't know
if it is or not!

Thanks in advance for everyones help.
-- 
Andy Quaas



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