I found a link to a pdf of the Swift fuel test report from FAA testing done last year.  Looks like there is a heat issue ( around 50F greater than 100LL) and peak HP is about 1.3% less than 100LL.

 

I know very little about the chemistry behind fuels and engine design, but if more heat is generated, how come that can’t be harnessed and turned into power?

 

http://www.tc.faa.gov/its/worldpac/techrpt/ar0853.pdf

 

Kevin