What are the most powerful modifications done to the 250? I'm planning a full efi with turbo. I'm sure it can be done with the right money!
if you want to make real power a turbo is definatly the way to go check out ford six.com and classicinlines.com theyre making a really cool aftermarket aluminum head, cams, carbs, valve train, headers, ect
Latest dyno test using an aluminum head on a 200 yielded a whopping 221 horsepower at the rear wheels. This was using an Autolite 480 and a DUI. It was tested on a Mustang with a T5 which gets 25-28 MPG. A 250 is going to yield even more but to date, no dyno tests have been done.