20* NO frickin way
Alcohol burns as a liquid not a vapor like gas, thus it fires off when conditions are right AND changes fireing as conditions change---- thats why you run a magneto because of the long spark duration, so that the spart will be around during those changes.
10+ CR gives you that needed kick to get things going before the blower comes in. Alc is extreemly hard to pre ignite (detonation) Anything less ( in reletive numbers)and you are just making a pig out of it.
On a cold motor if you had 20* of timing, you would prob fire of the cyl at 14/15 deg btdc and warmed up only have 20* in it??. Minimum I would start with is 29/30* at anywhere below 2000' corrected and 1* per 1000' after that
Its all about makeing the motor happy. The same engine I run, many years ago, because of class index, I ran 5 over on the blower, 29* of lead,and thru a lot of fuel at it (fat) to slow down to 7.60 and the motor was not happy about it. Now because of 7.0pro, I run 18 over, 34*lead, and trim the fuel back and use a high speed, now the motor runs clean and is happy (same spark plugs all year and 15 passes before I change oil)and still not even near a tune-up range that will start hurting parts.
The amount of blower boost/overdrive is what makes the combo mild, but basic motor/fuel princibles must be adheared to first and foremost
