"The List" of one engine is rather humorous to say the least. For years AMA refused to name an engine on the pure fact that it would appear that they were marketing towards a specific manufacture, so "the List" will NEVER be published by AMA.
In responce to Jim Allen and others making a desicion for the rest of us because other engines weren't "competative" is limiting new entries and new interest. Even if an engine like the "NT Evolution" isn't as competative, why should it be disallowed? There could be alot of guys that might like to give 424 a shot, but they don't want to purchase another engine just "to give it a try" . By allowing other engines, whether they are as fast or not, is limiting interest acrossed the board. I would think that allowing other engines ( St. GS 40, GMS, Evoltution. Etc: ) would possibly give a potential pilot a chance to see what racing is all about.
Now I know that some of our more expereinced racers have there blood pressure going up because the "Engine of the week" thing is coming to mind.
I know that back in the mid to late 80's, there were several engines that people were trying,
( OS, St. Como, Hp, HB, Mvvs, Irvine, Rossi, Webra, just to name a few) and aot of people were suddenly feeling the pressure that "my engine isn't as good as there's" or whatever. It turned into the "engine of the week" and people were getting frustrated that "all weren't created equal" .

Well Guess what, they aren't all created equal!

So why cant "The board", that ruled on the TT40 , from doing testing, produce an engine list with basic spec.s ? ( weight, Hp Rating, Rpm figures on a 9X6, and average price) Let the consumer make the choice. If the TT40 is the HOT engine and 424 pilots want the best possible speed, let them make that choice. But to say that an engine isn't legal because it isn't fast enough is possibly stopping growth and limiting participation . I know of a hand full of club racers that might like to go to a 424 race and try 3 pole, BUT they won't go because they don't want to buy another engine because there OS. St. GMS, Or Evolution isnt legal!
Lets open it up support the potential and realise what 424 is supposed to be and who our FUTURE racers might be .

Just my Humble 2 cents worth.