That's what I use, too (Kemcooil), one quart per tank of 93. That mix allows me to run initial timing of 6 BTDC without detonation. To run the full 9 BTDC I still need a mix of Turbo Blue 110 leaded/93 super unleaded at 50/50 ratio, so the octane boosting claims are not quite accurate. It does have a good amount of lead, though, and tailpipe emissions do smell very sweet! I bought a case two years ago and still have a couple of bottles left.

My engine is a factory spec untouched '69 400 YT, no head or piston work done, so compression is painfully high for pump gas.

Back when Marty worked for a GM dealer he'd bring me home cases of GM Anti Valve Recession Additive, which was very high TEL. My 'Cuda loved the stuff.