Here is a question for you sbc motorheads out there.
Its about the 350 I built for my Blazer. Starting around 2000 rpms, my motor starts pinging (especially under load from towing). At first, I thought it was a high compression/low octane problem but now I'm stumped. :confused:
The motor is a '96 4 bolt chevy block, .030 keith black pistons, low compression heads off of a '95 caprice (non LT1), just installed another cam, I don't remember lift/duration but its just a notch or two above stock (mid 400 lift range) performer intake, Holley 600 carb. If it makes a difference it's in my '85 fullsize Blazer with a TH350, 4.56 gears and 38.5" tires.
I always run 93 octane, run the timing from backfiring all the way to detonation, oil pressure stays a steady 60 pounds (autometer gauges). The day before I drove her from Florida to Michigan, it sounded like I dropped a lifter (chattering like hell). upon inspection, I saw nothing out of the ordinary, but threw a new cam at it just for peace of mind, that's a 1200 mile trip! I've even tried straight 30 weight oil still the lifters seem to bleed down and cause the rockers to 'dance' after a few miles which would seem like enough time for the oil to heat up and lose viscosity in Florida heat. If I snug the rockers down to stop chattering, the nut will actually bottom out on the stud and still chatter.
Upon changing the cam, I didn't see any signs of heat or wear, it just seemed like the lifters didn't have enough pressure to remain pumped up.
The only thing I can think of is that I didn't replace the bypass (oil filter adapter) when I rebuilt the motor. This is driving me nuts! She made the cross country journey like a charm but I had to keep it under 50mph the whole way. Is it possible to lose internal psi to the cam but not drop on the pressure gauge? This problem has plagued me for the 20K+ mile life of this motor. Spark plugs have never shown any kind of detonation wear either.
Any help as to what I am overlooking is greatly appreciated. I'm not a greenhorn building small blocks, but this ones got me scratching my head!!!
