Originally Posted By: 440Magnum
Incidentally, there's one other thing that's dead wrong in the article you quoted. It says that using ported vacuum is an emission control device used to lower hydrocarbon emission. Using ported vacuum at idle lowers NOx, and actually RAISES hydrocarbon emissions.
You are absolutely right! I didn't catch that one.
Now, the OP's car COULD have the centrifugal advance curve set up in such a way that it is advancing WAY too early in the RPM range (like just off of idle). Adding-in vacuum advance can push it over the top and cause the pinging. On engines that I set up for the street, I like to have the centrifugal advance start to move at 1500 to 1600 RPMs and be all-in by about 2700 to 2800 RPMs. But, with only a 8.5:1 compression ratio, he should be able to run a TON of advance and still not have it ping. Using 93 octane fuel, at that compression ratio he should be able to run as high as 52 degrees of total advance at as low as 2500 RPMs without a pinging problem. That is why I mentioned the carburetor power valve. It could be either... way too lean or not functioning at all.
All of the possibilities we are throwing out are just guesses. First off, we don't know what he is running for a cam or carburetion. And, until the OP puts a timing light and vacuum gauge on it, ALL we can do is guess about what the possible problem might be.
Incidentally, there's one other thing that's dead wrong in the article you quoted. It says that using ported vacuum is an emission control device used to lower hydrocarbon emission. Using ported vacuum at idle lowers NOx, and actually RAISES hydrocarbon emissions.
You are absolutely right! I didn't catch that one.
Now, the OP's car COULD have the centrifugal advance curve set up in such a way that it is advancing WAY too early in the RPM range (like just off of idle). Adding-in vacuum advance can push it over the top and cause the pinging. On engines that I set up for the street, I like to have the centrifugal advance start to move at 1500 to 1600 RPMs and be all-in by about 2700 to 2800 RPMs. But, with only a 8.5:1 compression ratio, he should be able to run a TON of advance and still not have it ping. Using 93 octane fuel, at that compression ratio he should be able to run as high as 52 degrees of total advance at as low as 2500 RPMs without a pinging problem. That is why I mentioned the carburetor power valve. It could be either... way too lean or not functioning at all.
All of the possibilities we are throwing out are just guesses. First off, we don't know what he is running for a cam or carburetion. And, until the OP puts a timing light and vacuum gauge on it, ALL we can do is guess about what the possible problem might be.
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