It should be the 50mm throttle body which is the OEM throttle body HD uses on the 96/103/110 engines since 2007.
The 58 mm throttle body is really too big for a 103 stage 2 and it is too big even if you have a 103 stage 4 unless you are running the bike over 3000 rpms all the time.
I had a 58mm TB on my 103 stage 4 and I hated it for cruising and I took it off and put the 50mm TB back on.
Stick with the TB you have and you will be fine.
But if you want a 58mm TB with 5.3 gram per second injectors PM me I have one here.
Go for the 58mm and you will love it. I know a local builder here that has been putting 58mm throttle bodies on 110" motors and getting 2 to 3 more HP and 3 to 4 more in TQ just by adding the larger TB alone. If you are going with stage II on your 110 the 58mm TB will be the cherry on top.
For basic builds no they are not needed but on a ported head increased compression build they work fine.
With the most tuners easy change of blade control if low speed manners are a bit jerky.
Testing has shown that the larger unit will increase tq not only in the peak number region but completely across the curve. Just did a back to back CVO 110 test with and with out the SE 58 . Nice % of increase
Picked up 7% hp and 4.9 % tq from stock t/b to 58 MM . IF you are doing a build and have correct items it works great.
IRON how much do you want for the 58 and 5.3 we use them on a very regular basis.
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