I have an 07 flhx. im im the process of doing a 103 build.
When first got the bike I added Rinehart exhaust, S&S VFT/Pro Tuner, and an S&S Air Induction intake.
What I have for the 103 are KB 10:1 pistons, Feuling Reaper 574 cams, Feuling Cam Plate and Oil Pump.
I'm wondering if I should also purchase a J.E.T. 48mm Throttle Body.
Any suggestions?

 

don't know much about the components you are using, however I have had 3 motors built (103, 107, 107) and kept the stock TB -- each motor ran flawless--

 

what are you doing for heads?? not keeping them stock i hope,

 

I see some bikes that are 103"/107" that are wild enough to need a larger TB, but in general for the average build I don't think one is needed until you split the cases and go Big.

 

Stock size tb on an 08 touring bike is 50 mm , so a 48 mm isn't going to hurt a thing.

 

Having the heads ported and polished, new guides, springs, and larger valves. And SE Springs

 

Then talk to your head man! He should be able to advise what cams and TB will be best.

 

It depends on what you do to your heads, i.e. valve size port size, I would stay with a stock tb as it will give better throttle responce on the street. If you are racing or dyno shootout then go with a bigger one, a larger tb will flow more air but you do need the rest to keep up with it

 

If we were involved with that, I would highly reccomend an HPI 51mm t/body, with a 1.710" manifold.
Scott