Ok, so I stopped by a local indy shop to ask about upgrading to a FM 107. He recommended doing an 106 kit instead, he said that’s what he’s been recommending and building and getting good numbers. His reason for preferring the 106 was that in his opinion going to the 107 requires thinner walls than the 106 and they tend to run hotter. Any thoughts on that?
He also recommends the 58mm throttle body and I’ve heard/read that the 50mm is fine for either a 106 or 107. So if anyone has thoughts on that, I’d like to hear them as well. May sound dumb to some but I don’t want this thing to be a total pig on fuel. Just looking for solid numbers for 2 up riding .
I do have another indy who does do 107 kits but he tends to take a while to get things done. Both shops have pretty good reps as far as quality of work goes.
I’m going to go all the way and have the heads done and do the crank with Timken bearing etc. I want this thing to be as bullet proof as possible. Looking at about $6k from both shops. I figure this is my last bike and I want it my way if you know what I mean.
I know you guys aren't shy about sharing your opinions so let em fly!

 

The 107" reliability issue has been discussed at length and I can't recall ever reading about any piston/cylinder failures. A benefit with the 107" is the seasoned cylinders (yours) are bored to specicially match the 107" pistons. 106" kits come with mass produced bored cylinders. Not saying this is bad but a precise fit is better. Your local indy is more likely a S&S dealer and makes a better profit margin on the 106" kit I'm a bet'n. The 58mm throttle body will help make better peak HP numbers. Depending on the extent of your headwork (if any?), you may just end up using your stock injectors. The crank $$ isn't a waste of $$ but might not be neccessary. Just have the indy check your run out and go from there. Good luck in your project ...

 

Your builder is a smart guy. I recommend the same things to my customers and friends.

106 with the thicker fins and the stock TB is a great combo

 

My bike runs fine with the FM107. I added a Jagg 10 row oil cooler and the factory runs a cooler on the 103.
Basically you do want you need to feel safe over. Piece of mind means alot.
Now I wouldn't pay that. Really with the kit all it is, is swapping parts. I mean look for scoring everywhere or wear and check run out on crank and bam your done. It is very simple job. Time consuming because I dont work on them everyday or I bet I could get three done a day.
Anyway good luck.

 

I think you would be happy with either, but IMHO I think the 58mm might be over kill. Bore your stock 50mm or maybe a 54-55mm tops and the stock injectors are fine for you build.

 

I have a 107 with stock bored cylinders and it doesn't run hot if the oil temperature is what you are looking at. I just installed a PowerVision so I should be able to monitor head temps now. Jamie, Fuel Moto, has done hundreds if not thousands of the stock over bores and for the most part I have only seen positive feed back. You can get 107 kits that have after market cylinders such as Revolution Performance or Axtell. Axtell has pistons available that have a 20 degree camphor circumference which the porter that did my heads (Mike Lazano, New Braunfels, Tx.) says will cut down on detonation and make excellent power. If I do a 117" in the future I will use Axtell pistons and cylinders.
I suppose you are talking about the S&S 106 kit when you say 106. One nice thing is you get a new crank which means you don't need to have the stock one straightened, plugged, and welded. These 106 kits make some outstanding power, especially at the lower RPM's. The only Harley I have ever ridden that would spin the rear tire just by cracking the throttle had a 106 kit in it. One of the local indy's did one on his personal bike and it will do the same thing. As for the throttle body, if you are looking for top end horse power the 58mm is an option, but on a 107 or 106 I would say the stock 50mm would be sufficient and give you the low end that you probably want.