There seems to be quite a few mis-conceptions about throttle body diameter size on B-series VTEC engines. When a manufacturer states the throttle body diameter, they refer to the inner diameter (ID) not the outer diameter. Measure the ID with a set of vernier calipers to find out for yourself (Refer to Fig 1.1). The figures below show stock Honda TB IDs.

B-series DOHC VTEC engines:

1st gen. B16a: 58mm

2nd gen. B16a: 60mm

B17a (USDM): 60mm

B18c: 60mm

B18c (Spec R): 62mm

B16b: 60mm

62mm bored out 1st gen. B16a TB

Fig 1.1

Spoon tapered Type R TB

Other:

H22a: ?? (someone please enlighten me, I think it's 60mm)

Spoon: 70mm OD tappered to 62mm ID

Holley: 64-68mm!

BBK: ??

Spoon TB has 16% more volume over stock ITR TB. It boasts more mid-range power (approx 5hp) and ON/OFF throttle response.