SU's come in several sizes 11/4" , 11/2", 2"then there are CD SU's as used on XU1 Toranas and lots of pommy cars like Jag's,there are new types and old Types. i think there is another size also,but the funny thing is you measure across the inlet where it bolts to manifold and they are not exactly 11/4 or 11/2 but smaller as is the 2 inch and also they have different bolt patterns for air cleaners but most air cleaners have mark outs to drill for different carbs,as for whats best it all depends on how modified your engine isof course a stock motor will probably flood with tripples but for a warm grey with slightly higher compression ,stronger valve springs ported head, warm cam and regraped dizzy the 11/4 would be good, for a head with big ports big valves hot cam regraped dizzy with good coil and strong bottom end preferably with bridged crank and better high comp pistons then 11/2 , ive been wrong before but i have run this set up before and it worked well with a bit of fine tuning (every week end)
