Today's flying was much more than just a couple quick flights. I was to meet Ed at Jim Martin's field this afternoon but I had early trouble with my elevator pull-pull cables...I must have jammed the elevator putting it into the van and the down side came loose. By the time I got that fixed and got on my way, Ed called saying he was on his way back home. Not a good way to start the afternoon.

When I got there, Jim was packing up, so I asked if I could have a tankful of his 100LL Avgas. Changing nothing in my settings, I started the engine and took a quick hop. The mid range was extremely rich but the top end was pretty good so I made several passes. After a couple minutes the engine died for no apparent reason. Investigating, I found that my check valve that I've used forever on the vent line, simply stopped working. OKAY THEN!!

Restarted with leaner low end and very slightly richer top end and took a whole flight. Very interesting results. Engine was back to its normal self on the 18.1x10. Extended vertical was ever so slightly worse than when running the 87 Octane regular gas but no sagging noted.

Decided then to try the 17x12 apc which is a standard we all understand in pattern. Took a very quick hop because the low end went fat again. Landed and leaned it out a small amount plus richened the HS needle some more. Much better but still not quite there using the 100LL. Talking with Jim (who has flown CDI stuff for many many years) we realized that the 100LL retards ignition just a little too much. If we had a CDI unit that automatically advanced ignition a couple degrees, we would be able to run a fatter midrange and drive more power in the midrange. Ed, there's an opportunity there buddy!!

Learned a lot: 100LL Avgas smells great and has more than enough pop. Requires different set-up than 87 Octane regular gas. 100 LL retards ignition too much as is....I think a mix of 87 and 100 could be just the ticket, unless there is a 90 Octane Avgas altrenative. The 17x12 was turned superbly, just like on glow. 100LL Avgas runs cooler in the engine, but Jim thought that the flame could be propagating into the pipe more and to keep an eye on that.

See, high Octane burns slower than low Octane does so the indications of retarded ignition is on par. Since it burns slower, it is reasonable to assume the burn could be proceeding out into the exhaust a little. However, the engine was pretty cool when checked after landing, even in 90 degree conditions. There's an awful lot going on in there.

If anyone gets a chance to try 93 Octane in a piped set-up before I do, please report your findings