Is it possible that the SIR size could be determined using Marshall's line of reasoning on CR? Calculate which current engine has the smallest total intake cross-sectional area and apply that to the rest of the engines. The problem I have with having a Dave Finch working it out is that I'm sure he won't do it for free. I don't have the money to do it and I doubt that anyone else will. I also understand there were some hard feelings in the GTL ranks when it was announced that all competitors had to buy their SIR from him. I may have some facts incorrect, but I plan to make my own SIR. Isn't that the point of a "free" class?
I'm inclined to stick with F1000 and limit it to liter engines. Sean's opinion carries a bit more weight since he actually has a car. If there is a group that is interested in F600, they're welcome to follow along, but they'll have to do their own leg work. I'd like to keep this "project" uncluttered. It may be more convincing when it comes time to sell it the SCCA.
As soon as I have some free time, I'll redraft the rules and post them to continue the momentum. I would also like to start thinking about putting together a proposal and pursuing Dave G's suggested course of action. Please keep the discussion going.