ANY OTHER ADVICE??

[Mr. Chevy]

I am working on a 1967 Impala with a factory 327/275 HP motor, 4 barrel,and powerglide trans. The motor is factory stock with 37,500 miles. It has been sitting for 5 years and I recently got it running. I have gone completely through the ignition system changing everything with new parts, checked the timing setting it between 6 and 8 degrees before TDC per factory specs, flushed and refilled the cooling system, opened the heat riser and changed the fuel filter.

I have a detonation issue while under a load. It is driving me nuts. The hotter the motor gets the worse it is. When the engine is cold it does not do it.. It sounds like it is restricted to the passenger side head area. The motor otherwise runs fantastic. I have had all kinds of thoughts from friends and mechanics about different issues that might be causing the problem. The gas in the tank that had been sitting for 5 years was siphoned out and Shell 89 octane was put in about one month ago by the prior owner. One old time mechanic told me this is the issue. He said that octane rating is too low for that motor plus there is most likely a carbon build up.

Research shows the compression rating on this motor is 10:01. The heads are the double hump heads. My thought is to drain ALL of this fuel out and put in some 110 octane racing fuel mixed with Sunoco 93 and then BLOW OUT THE CARBON. Trouble is the tank is 3/4 full...

Any ideas or thoughts from anyone???? It could simply be just this fuel issue and maybe bump the timing down a bit...

Thanks.....Rich