Doug,

The TT Pro 40 has never been in the actual core of the R/C Pylon Racing section of the rulebook. There was a web page with the Thunder Tiger Pro .40 as the approved engine. I haven't looked for it lately and the web site hierarchy has changed in the past year or so. It may still be under the Competition Documents section somewhere. I got the link from Steve Kaluf and I don't know what I did with it. I think it was an addendum with multiple tidbits for Pylon Racing. Or it may have even been on a preface page in the R/C Pylon Racing PDF file and I could be wrong.

One of the Contest Board members can probably tell us where to find it. Speaking of which ...

Dan Kane submitted the proposals that were added to 424 for the 2007-2008 cycle. As far as I know Jim Allen was/is the head of the 424 engine committee.