Dick I have done a lot of experimenting with different fuels on my ZDZ 80 single and my 160. I went so far a to buy the racing stuff you know $80.00 Canadian for 5 gallons. Now you have gone the other direction and retarded the timing,which is the same as adding octane,because of the increased cylinder pressure. Anyway what I found on a full length tuned pipe the racing gas was good for 100 rpm over aviation fuel. Idle and mid range were slighty better, but no enough to justify the cost. Our 91 premium fuel works very much like the aviation fuel but smells a lot more. I did not try 87 octane. I spent weeks fooling around with this I tried different header lengths with differens fuels,it still comes down to what you want to accomplish I was looking for a quiet set up that would give me the most power on a particular prop that being a bolly 32x12 on my 160. I did not tune for top rpm as that was simply to loud 5900 rpm.