I'm thinking of selling my KB Hypereutetic 103 pistons I bought recently and are still sitting on the shelf and opt for the slightly larger 107 CP versions to install in my 2008 FXDWG.
Now my question is will my stock throttle body be adequate or would the bigger 107 with mild heads and cam require a 50mm body?
Thanks

 

It's going to depend on head work and cam selection. You referenced "mild" head work but no mention of cams. If stock valves are retained as part of the head modications and you select "bolt in" cams, sayu cams with no more than .550" lift; I don't believe the stock T will hold you back. However, if you go with bigger valves and longer cams, say like TR625, then the stock TB will likely be a bottle neck. Is 50mm big enough? Don't know.

 

I was thinking a mild port and maybe 1.90 ex valves with a cam that can be used w/ stock springs only.

 

I think you mean 1.90" intake valves?? Not sure what you're expectations are or how you ride the bike but a BigBoyz street port with Andrews 48H cams or TMans 525 or 555 with the increase in displacement will wake things up and the stock TB should work OK. BigBoyz street port is a velocity port job and Bean likes to retain the stock valve sizes but will go bigger if requested by the customer. You can pick up some respectable TQ/HP without breaking the bank.

 

Thanks for the reply, very informitive. I guess I did mean 1.90 intakes. I've heard a lot of good things about Big Boyz.

 

Just finished my 96 this winter, just port work and mild cams (204's). The 96 std head actually flows pretty well. I was flowing with the throttle body and was frustrated with the progress and realized the TB was a big part of thre problem. Went to an aftermarket 51mm body with the smallest runners available (1.6 I believe) and the numbers on the bench took off. It's not just size but shape and plenum. In hindsight not sure I would have even done the heads. So my answer would be yes, pitch it. Came off the dyno at 100 ft/lbs and 90 HP which the dyno guy tells me is pretty good for a mild build and mild cams... My opinion only..

 

Another story that squashes the theory of "bigger is better", eh? Impressive numbers.
Thanks for the info

 

When WE set up a 107"er, we usually end up with a head that'll be running north of 165 cfm @ 10", @ .600 lift.
That IS NOT a stock valve, or a 1.900"er either.
Many times we are using a head of ours that moves 172 @ 10" @ .700 lift.
We want to see the head pulling past the cams peak lift, while still concentrating on the mid-lift flow characteristics.
ONCE that is established, with the proper t/body,(usually a 55mm HPI) and cam/compression, big power, easy tuning, and cool running are what is to be expected.
Scott

 

My little 95" with the stock 46mm tb spun the drum at 104/100, know guys with 113's running nothing larger than a 50mm, there's even been some 120's running a 50mm and making pretty decent numbers. Sometimes bigger works and sometimes bigger is a waste of $$$, depends on what your looking to accomplish.

 

Looks like it will be a good idea to choose a tuner and pick up the phone! We can chew the fat here, but there is no substitute for talking to a specialist in person, with a view to giving him your business. That way you'll get a complete and proven package of matching parts.