Ah, but a T309 is a 3-cylinder T3 and a T312 is a 4! The only T4 I'm aware of is the T409 Tiger 900, which is a triple. Much like my 2004 T625...
Not simple like the old days, when a T120 would theoretically go 120MPH and a T140 would do 140.
Oy. Sometimes, I think I could remember my cousin's birthdays if I didn't have all this crap cluttering up my brain.
Cheers,
-Kit