2008 to present Delphi fly by wire, (FBW) 50mm, no throttle cables.
The early 2008-2009 throttle bodies can be bored out to 54mm by making the throttle plate larger. I also go inside and clean all the casting debris out and radius the corners. I also match the port runners to the heads. These can be from 1.650 to 1.800 depending on the size of the motor.
The late model Fly By Wire throttle bodys 2009 and up are not workable.
The factory changed the inside dimensions and made it so it can not be bored any larger.
This is where the S&S throttle hog and the HPi throttle bodies can be used. The companies have casted new throttle bodies that can be from 50mm all the way out to 70mm. We need to use the stock internals from the original throttle body and use them in the new castings to make a throttle body the size you want or need.
Here is an example of the differance with the early and late FBW throttle bodies.
2001 - 2005 Delphi single bore
Harley started using these in 2001 and they were a great improvement over the M&M efi throttle bodies. It has a 43mm throttle plate that is necked down to a 41mm just behind the throttle plate. I upgrade these throttle bodies in one of two ways:
The first is to bore out the throttle plate to 48mm and the area behind it to a 44 mm. this will allow the use of the original o-ring to seal the manifold to the throttle body. Next, I bore out the manifold to match the throttle body. I also will port match the intake runners to the runners on the heads. I have found that a 1.700 opening is just about perfect.
The second method is to bore the throttle body out to 48mm all the way through the body. This leaves a very small sealing area between the throttle body and manifold. It can be sealed up and work well but it must be checked often.
2006 - up 46 mm cable driven.
This is Harley's best throttle body to date. Works very well at 46 mm but can easily be enlarged to a 50mm. This is a basic change. I replace the throttle plate and blend all radius's in the body of the throttle body. Then I open the port runners to the match the heads. Here again I have found 1.700 to be the best overall size.
1995 - 2001 Magna Marrelli
This is not the best unit Harley ever made. It is not rebuildable and is a pretty poor design. Some claim it is a good unit and have made it work successfully. Most convert them to a carbutetor model. I simply replace it with a nice single bore HPI throttle body. The single bore is expensive but worth evey penny.