looking at installing new throttle body which one of HPI units 51mm or 55mm and injector size.

 

If you get the SE 50mm it comes with the larger injectors. Are you doing head work and what cams. What exhaust.

 

I run a 107 in my wide glide. Running stock throttle body (cleaned up and polished) but swapped injectors to 4.9's. 124lbft of torque with big radius 2-2 pipes. Heads are fuel moto's "b" heads

 

hillside stageII heads, woods 555 cams, thunderheader 2into1