Originally Posted by LA_Dog

Well I guess we might as well make an old post current and relevant for anyone else who reads it

I looked into the SE 50mm TB and I believe it only fits the SE heads- I could be wrong, but there is no way to confirm if it fits stock heads.

What I'm doing now is, I picked up a nice condition used 46mm TB off ebay for $50. I picked up a set of 4.9 SE injectors for $100. I'm having George at maxbore.com hog the TB out to 50mm or 51mm and cut a new butterfly, $125 total.

Main reason I am doing this is my current stock 3.9 injectors are maxing out at 100% duty cycle under high MAP and mid to upper rpms. that is bad for tuning accurate fuel delivery as it should always be kept under 85% max IDC. And since I'm swapping injectors I might as well pop on a slightly larger TB for not much added effort or expense.
Right now, the 46mm TB flows less than the stock heads, so a 50/51mm is not "too big" at all in this situation, it's actually more appropriate and correct of a size for the 103. I'll be adding a 204, 54, 57 set of cams later on (one of those or similar mild cam, TBD).

But- if we are talking straight "bang for buck", as mentioned the 30/70 pulley upgrade would give much more immediate performance benefit vs a mild cam and TB upgrade. Even though it's well higher in cost. Doing both of these upgrades though, will work together beautifully. It's actually a rather economical spend of est. $1300 total for a lot of added grunt.

You do however need a powervision, fp3, tts or similar tuner to be able to dial everything in and also set the speedometer correction correctly for the pulley changes.- that's another $300-$500.

But hey- What's almost a couple grand on Harley performance upgrades? Chump change right? LOL