Here's a thought. You want to make it as cheap and as accessible as possible to attract participants. The more participants you attract the more viewers you attract. Most engine builders will have stuff lying around collecting dust or have access to a cheap core and since 318's are junk in most peoples eyes that would represent a good candidate for the participants.
2nd thought. Make it about average HP per cube so as to challenge the builders to build overall power efficiencies instead of just a peak number. Make them use factory parts so as to keep the costs down and showcase builders smarts not their check book. Then when it's said and done use the relevant builds to educate the viewership on the builders approach and show case his/hers ideas and what and how it was accomplished.
In my view its not about the engine you use but about the ideas and know how and what people can learn from the exercise.
