PursuitSpecial
Well-Known Member
So after I gave up on the thermoquad and put it on my 400, I switched to a Holley Economaster for the 318. It really doesn't run any different, though it has much better cold manners. Anyway, now I'm noticing that the car is spark knocking very badly under moderate loads like would be encountered in everyday driving getting up to speed, but it only does it in certain weather conditions. It's an audible tap-tap-tap sound that manifests only under acceleration. Last weekend it was 25F with a barometric pressure of 30.54 inHg and humidity of 75% when it did it, the engine was as warm as it would get. Once the pressure dropped and the rain moved in this weekend it stopped. I have already experimented with timing, it is as conservative as it will get without hurting the power too much. I currently have it at 10 degrees initial and 30 total with a stiff advance spring so it won't see total until about 3000 rpm. There is 6 degrees of back and forth slack in the timing chain. I fed some water down the intake with the engine revved up and it didn't blow any carbon out of the exhaust. As it is a bone stock 318 HP engine it should have 8.2:1 compression due to the larger 360 heads. The engine has a history of doing this. When I first got it out of the woods and started driving it, it would knock on regular gas, the only way to stop it was to lock the timing at less than 20 degrees and make it a dog to drive or burn premium in it. I experimented by running a tube to the carb and feeding it pure oxygen out of a tank at different concentrations and it would knock very, very badly. For some reason it seems this engine is incredibly sensitive to atmospheric conditions and fuel octane, which it definitely shouldn't be ast such a low compression. The only other thing I can think of is spark plugs, I'm running a 0.750 reach plug, which should be correct for 360 heads, unless they were different or something in the early 80s. Any ideas what's going on?
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