well, what more do you need? Spec 3 was based on "old" EFRA specs that limited crank scoops severely, the scoops could not extend into the crankshaft passage. The newer rules don't have that limitation. That was the main diff in the rules, I suppose the timing has also been altered in addition to the crank. I have never had a Spec 3, but I've used Spec 2 and 4.