Make sure your balancer mark is indeed at tdc on the cylinder #1. They do have a tendency to slip and if original it is over 50yrs old. Next with the timing light read the power timing thread the wizard posted and do the measuring and marking to see just what you are getting for timing as the distributor brings the mechanical advance in and where it is "all in". I'm guessing the plugs look decent for fuel. But with the detonation they can be unreadable. Wires in good shape and ohmed out for the length.
When you say the engine runs warm, how warm is that? What do the spark plugs look like? The top of the piston looks bad. While it’s harder to do now, but not impossible since you have a head off, you should really measure and calculate the cr from actual measurements.
to Larry's point, the stock pistons did sit below deck but if that measurement is somewhat accurate these pistons are .080 below... thats pretty far, and with that measurement would be tough to achieve 9.3 as you calculated. I run the calculation on my 462, mving the piston from .008 (my deck clearance) to .080 (indicated on your measurement) brings my compression from 10.0 to 8.7. I think we need more accurate deck clearance measurements, and I'd like to see what numbers youre plugging in for CR/DCR, and whatever other specs you have including deck and pin height spec on those pistons if you still have it.
Based on everything so far, ignition timing is retarded if anything. That actually looks kind of low overall. One other thing that can cause detonation is excessive oil getting into the combustion chamber. The piston tops do not look great. Does the engine use oil? How do the spark plugs look?
I agree with Larry. The condition of those pistons is from oil consumption. I would check the valve seals or the intake gasket.
Thanks for all the advice! I will measure again today to make sure it is accurate. I have tried 2 different balancers and verified that the timing mark is approxamately in the right place (it almost aligns with the keyway). It does not go through significant amounts of oil. About a quart per oil 4000 miles. The spark plugs are generally fine, perhaps a little black, but i assumed that was from the carb. I will put the numbers together for my CR calcs and get those posted.
There aren't that many things that cause detonation, Too much compression (static or Dynamic) for the octane of fuel being used. This can occur from using too small a cam coupled with too much static compression. I don't think that is the case with your relatively low cylinder pressures. Cam timing being wrong causing higher Dynamic compression. Again, I don't think so. Excessive coolant temperatures Too much total ignition advance. Hot spots in the cylinder. Sometimes this is due to deposits, or wrong heat range spark plugs. Not likely, AC R43TS plugs should be fine. Lean fuel mixtures caused by wrong jetting in the carburetor or vacuum leak. Oil getting in to the combustion chamber. Maybe.
Whens last time you checked the sock in the gas tank. Had that problem with my 350, motor was always starving for fuel. After converting to a big block and redoing the entire car, when I put a new gas tank in I found the sock compressed basically like sipping through a closed straw. Something to check out. After I found it told some people and answer was oh yes that always happens.
Here are my assumptions for the CR calcs. i used a calculator at butlerperformance.com. Bore (60 over) - 4.100 inches Stroke - 3.9 inches piston relief volume - 12cc (per TA performance) Felpro head gasket compression thickness - 0.041 inches Head displacement - 69cc deck clearance (previously calculated) - 0.050 inches CR = 9.38:1 Using measured deck clearance - 0.075 CR = 8.96:1
I have tried 2 different carbs - one that runs leaner that the other (based on emissions testing in Phoenix.). no change in pinging. Hot spots in cylinder, maybe, lots of carbon. I have not checked the sock in the gas tank, been years since i have dropped the tank. But the car doesn't seem to be running out of fuel. Just pinging.
The car runs hot during the summer, not the winter. I recently put in a much better radiator and a TA performance hi-flow water pump. While i used to see temps on the freeway of 225 F, that isn't the case now. But as i mentioned, it pings at 50 F outside and the car bouncing off the thermostat.
I will measure the deck clearance again tomorrow. Is there a more accurate way to measure it than the caliper i am using?
The motor is running hot and pining for 2 reasons from what I can clearly And without question see going on! 1) all of that Carbon build up from whatever oil source is a bad thing! The Carbon heats up and glows red hot like charcoal embers once you open the throttle enough to get the cylinder temps up high enough and the creates ping and knock, oil getting into the cylinders also reduces your fuels octane rating and exasperates that condition! 2) your low cylinder pressure makes getting the hot Exh gasses out of the motor a harder and slower process which retains excessive heat in the cylinders and ontop of all this is that excessive deck clearance with the new Pistons that does not help to pump out the hot gasses. All of this adds up to one issue creating yet another and more damaging issue for the motor, think of it as a circular firing squad! If your motor was sealed up well and built with the right pistons and the needed Cam then even a 9.5 compression would not be a issue. Motors are built all the time these days making over 165 psi of cylinder pressure even with iron heads and they run fine with no ping and make well over 600 hp on 87 octane pump fuel, no less 94 octane! Another good reason to not run a cast piston these days besides the strength issue is that cast Pistons run 100 degrees hotter on there deck surface then a forged piston does, this makes Carbon built up even more deadly. These are all conciderations that should not be overlooked these days even on builds where only 350 hp is wanted out of the motor. PS, by the way when I run the numbers for you compression ratio with a .075" deck I get 7.95 to 1 which to me explains your very low cylinder pressure assuming your rings / leakage is ok. Note that this ratio I did was without factoring in the 1.5 to 2 CCs of ring land volume that every motor that does not run gapless rings has to yet further low the compression ratio. It's beyond me why all of these high tech on line comp calculators do not add in atleast 1.5 CCs when they run the numbers?
did you ever check or unhook your vacuum advance and drive it. what was your total timing with advance hook up. seems if it was that lean it would surge. could to much piston clearance sound like its pinging ?
This is what I get for static compression with your numbers, And DCR with the TA Stage1 cam set at 109* ICL,
The most accurate way I have found to calculate compression is to convert all numbers in cubic inches into cubic centimeters. To do this just multiply your numbers in CI by 16.386. Bore 4.100 x 4.100" = 16.81 CI. 16.81 x 3.900" ( stroke )= 65.55 CI. 65.55 x .7854 ( turns a square into a cylinder ) = 52.49 CI 52.49 x 16.386= 843.71 CCs per cylinder. Combustion chamber volume = 69 CCs Piston dish =12 CCs. Deck clearance = 16.81 x .075"= 1.260 x .7854 =.9896 x 16.386 = 16.21 CCs. Head gasket= 16.81 x .041" = .6892 x .7854 =.5412 x 16.386 =8.869 CCs. This all added up is 106.08 CCs which you then divide into the cylinder volume of 843.71 for a compression ratio of 7.95 to 1.
Have you checked your total timing? The issue may be that your advance slot in the distributor is too long because the bushing is no longer there.
