Im having a 107 build done and it was suggested to me to go to a 50mm throttle body rather than the stock. I figured i would only need to change the injectors and not the body. Will there be enough gain to justify a 50mm ?

Also I thought a K&N high flow air filter would do fine but I keep being pushed to Bob Woods air filters. I don't know. Wanted to ask the pros. Thank you.

 

You will lose low end TQ for a higher HP number. It depends on your build. What cams, compression ratio, etc. Personally I would not for that build. Actually, even in HQ's 113 build stock TB is used for some serious tq numbers.

 

If you are chasing the biggest possible hp number you can get out of it, then the larger tb will make some difference. Depends on what you want or need. Me personally with my fxstc I want usable power and don't expect to rev to 6k anyway since 56-58 is plenty on a B motor. For me, the stock tb and injectors will work just fine. I can't justify 800 bucks for a few more hp, since torque turns me on more. Depends on what turns your crank, and how important those dyno printouts are to you. To me, they make a good a$$ wipe, nothing more.
Ron

 

If I understand correctly, it's S&S kit . 106 jugs with pistons. Had my heads reworked, woods TW7 hg cams , D&D Fatcats 2 into one.

 

Depends on what you want. I am using a SE 50mm (with 4.9 gm/sec injectors) TB in a 2007 107" FLHX and was running out of injector pulse width at around 5,800 RPM. At 6,000 you only have 20 ms to complete your injection cycle. I was up to 19.6 ms pulse width at 5,900 RPM. I can't go over that without the AFR going leaner than the desired AFR on my build.

If all you want is lower range throttle positions your stock TB is fine but if you are going over about 5,800 RPM I would up the injector size and the TB size.

If I had to do it over again I would have HPI rework my stock TB to 48mm and use the 4.9 gm/sec injectors.

B

 

+1,mike stedman at latus motors told me the same answer when helping a friend with a 103, stock inj are maxed out at about 100 h.p.

 

HPI ? Who is that ?
I was told that the 50mm throttle body would let more air in and help the bottom end and give better over numbers. Im not really looking for top end 5500 to 6000 power. 90% of my riding is done between 2400 and 3600.

 

HPI= horsepower inc.

They rework the stock (on a 2007) 46mm TB to 48mm and rework it to flow better. About $200 plus new injectors.

Or you could go with the 50mm TB from H-D for about $330 discount price.

Or you can stay with stock and set your rev limit to lower if necessary depending on your HP output.

I believe that torque will not be affected either way but if you run a good 107" build to above about 105-110 HP actual (not corrected) you will start to have your AFR go leaner than desired as the injectors can not deliver enough fuel in the time available. Depending on your build and cam you may not want to go to the higher RPM anyway. If you are on the downside of your torque curve you may not need to go up to the higher RPM.

B

 

The S.E. t-body is not a must you would see gains but the minimum you need is a set of injectors. harley injector kit is like a $150 the tbody is like $400 so thats a choice only you can make.

The S.E. 50 mm throtle body is a good deal compared to other options. you get 4.9 gm/s injectors which is more than enough for your build all new sensors and its a one piece unit. which i like instead of having the possibility of another intake leak. . I've done before and after test with a stock t-body vs a 50 mm on a similar build only a 103 and suppertrapp exaust and their were gains in both the hp and torque curves across the board.

Your k&n high flow is proablly a stage 1 in size which allows you to use the stock twin cam cover the problem with that is it tappers inwards which limits the amount of filter media. A stage 2 filter tappers outwards which increases the size of the filter thus increasing flow. and woods takes it even a step further with a larger filters. the bottom line is it dosent make much since to spend 3 grand or more on a motor and choke it down by not buying a 80 dollar filter.

 

I've heard a lot about filters lately. I remember when I had my Bigdog. I remember the size filter on it and it was a 117 ci. Now people are saying we need high flow filters. I thought that was what K&N was selling. Bob woods claims to have the best high flow filter around made by K&N . It would be good to see the comparisons.
Im game with the bigger injectors for sure. Don't see where the throttlebody would do any good on this build. the gain im guessing wouldn't even be noticable. Im interested in getting "usable" power more than top end . But it's good to have it when you need it. You say you've seen gains with the 50mm throttle body on simular builds. Would be great to see those differences.
I think im going to be much happier with this build rather than the build Harley did. Dont get me wrong. it was a nice build for Harley parts, but a lesson learned on a name being printed on the side of a head.