Do I need a SE or equivalent throttle body for 128 build?

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Feb 27, 2020 | 10:18 AM

#11

Steve Cole

HD EFI Guru

Joined: Jan 2008

Posts: 4,462

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Quote:

Originally Posted by D W K

All,

I am in the process of doing a FM 128 on my 17 CVO.
Currently have S&S 475 Can, S&S quickie push rods, S&S tappet hold downs, de catted stock head pipe to SE Street Cannons,and the CVO air cleaner.
I have purchased the SE 5.5 injectors,

Do I need a SE or equivalent throttle body? A builder recently told me they gained 10 Hp with the throttle body alone on one of their big builds but stock 114 injectors. .

I am not trying to build a monster powerhouse. however I dont want to unnecessarily leave a bunch of power on the table either.

Thoughts?

You need to define what it is your looking for.. The throttle body and intake need to be replaced if your looking to get all you can, so where is it not worth it, really plays into this. IMHO using the SE replace intake is a must as we have seen that improve a stock 117 engine output, this is using the stock throttle body still. Now as the engines get bigger the restriction point the throttle body itself comes into play. From idle to ~4000 RPM we have seen no improvement from the larger throttle bodies, all improvements are at or above that RPM. Now go to a 128 that RPM point might move slightly lower in the RPM say down to 3800 RPM. So is it worth it for you based on the RPM range you ride the bike in has to be answered only by you.

Feb 27, 2020 | 02:11 PM

#12

D W K

Thread Starter

Road Captain

Joined: Aug 2012

Posts: 579

Likes: 38

From: Texas

Quote:

Originally Posted by fuelmoto

In the short cam, mild 124/128 builds with stock heads upgrading the throttle body is optional and the gains are going to be in the upper right side of the curve. It really depends on what you are looking for from your combination, generally speaking you can expect gains of about 3-5Hp with a larger TB in this application, however if you are doing a higher output combination with headwork & more cam the larger throttle body will play a larger part in overall performance.

Thank you, this is exactly what I was looking for. So just to make sure I am understanding correctly. With the FM 128 kit, S&S cam, Stock Head pipe gutted, SE Street Cannon mufflers and stock CVO intake. The throttle body and intake will yield power in the right hand side of the curve, but not as much unless I go with the head work?

What about the 5.5 injectors? Yes or no on a stock throttle body and intake without head work?

I am asking all of this as this build is out of the blue and not something I saved and planned for. The 128's has as much to do with cost effectiveness as they did with want / need.

Honestly a 130 /130 build is fine with me. I am not looking to eek every HP out of it. I just want it back up and going. And not sumping of course.