I have a 1970 Cadillac with a 472 V8 that has a bad spark knock issue. First, let me start by telling you it has been converted to an HEi ignition. I have replaced the ported vacuum switch, checked and rechecked the timing, checked the plug gaps, etc. and it’s still knocking. I thought it might be the TCS switch but finding that part is next to impossible. Can you please tell me what I can do to fix this?
This may be one of those modifications for which there is no published specification.
That engine had a 10 to 1 compression ratio and was designed to run on leaded fuel, with a certain amount of camshaft timing, and a certain amount of ignition timing.
Odds are the advance curve of the HEI is different than the contact point distributor also.
This means that you may have to retard the timing as compared to what the original spec is and possibly learn to live with some reduced engine power. No matter what, a bad spark knock cannot be allowed to continue or the valves and pistons may be kissed goodbye.
Another possibility would be to consider installing a later EGR equipped intake manifold. The EGR can make a huge difference when it comes to a spark knock problem. The 500 intake up through 1976 should fit.