I am considering this mod but would like to hear from some of the experts. Please see below...



Our goal when we started our project was to offer our customer’s a high horsepower throttle body option for a lower cost than what is currently available. Right now, big throttle bodies are available from Screamin’ Eagle and other aftermarket manufacturers at costs between $400 and $800. They all produce good results, but the total cost of installation and tuning can be over $1000. For just a small increase in performance, this can seem a little expensive to many people. Instead of having to purchase an expensive new unit, we set out to see what we could accomplish by some simple inexpensive modifications to the stock unit.
All ’05 and later Twin Cams (except for ’08 FLH’s) come with a one piece 46 mm throttle body. Upon testing we found that this 46mm unit was limiting customers to about 92-98 HP depending on displacement and the level of performance work. We found the overall design of the part to be a little lacking (it was clearly designed without performance in mind). The port runner increases in diameter from 1.900” to over 2” after the butterfly and still gets larger in area until the port exit at the cylinder head which is 1.640.” Any intake manifold that is designed to increase engine performance has port runners that are smaller then the butterfly, which also has a constant taper to the cylinder head. This is done so that the air in the throttle-body is constantly increasing in speed (this reduces reversion and increased throttle response, it also helps prevent detonation by keeping the fuel in suspension (low velocity and reversion cause fuel to fall out of suspension which increases the likely hood of detonation).
We flow tested the stock throttle body and found out that it flowed 219 CFM at 28.” We then bored it out to 48mm (.090” bigger than stock). The manifold was flow tested with just the bigger 48mm butterfly and we saw an increase of 13 CFM (232 @28”) We then did a little bit of clean up porting and re-flow tested the throttle body with results showing an increase of 22 CFM (241 CFM @ 28”). After flowing the throttle body we installed the unit on a 103 cu” TC with a mild camshaft and 9.8:1 compression ratio (baseline power of 92 HP and 104 ft lbs torque). Upon installation of the 48mm High-Flow throttle body and proper tuning; the HP increased to 96 HP and the torque increased to 106 ft lbs. SEE DYNO Seeing as the 48mm worked so well, we thought we would push it a little further and try going to 51mm. After re-boring the throttle-body to 51mm (an increase of .196” over stock), we flowed the throttle body and that’s when the bad news started. The 51mm throttle body only flowed 243 CFM @28” an increase of only 2 CFM over the 48mm unit. Seeing as the flow bench is not always a tell-all in performance, we then installed the part on the same 103 cu” TC as before and proceeded to test and tune the 51mm throttle body. The results were not good; the HP and Torque both went down about 3-4 units in the low and midrange RPMs, but the power above 4750 RPM increased by about 4. SEE DYNO All in all I would say that the 51mm ported stock throttle body was a failure, because not many people spend a lot of time riding above 4750 RPM, but we were determined to make the 51mm throttle-body work. We thought about what we could do to increase the velocity behind the butterfly. Increasing the velocity and the CFM would increase the power everywhere and make better use of the big butterfly. The port runners were then cleaned up and some very high-tech epoxy was used of fill the ports (to replicate the port runners of our J

 

Very good work there STD. I have a friend that has been doing some extensive work on the 46mm TB as well, I hope to have one in my hand any day now to test myself. Any time you can see a gain of 5hp and 5tq your work was very successful....not to mention a 7hp gain.....good job!!!

 

I guss I'm confused on the first dyno graph??
Nevermind, I think the graphs are mixed up? Looks like the second graph is the 48mm graph and the first graph is the 51mm graph!
The 48mm looks like it worked very well!!
How much is this going to run?

 

Johnson Engine Technology

48mm bore job = $170



Steve

 

That message is, for me, unreadable--how about some double-spacing between paragraphs and shorter ones as well????

 

Doc, I am looking foward to seeing the results of your testing.

 

http://www.johnsonenginetechnology.c...ttle-body.html


Steve

 

While I can't speak to the quality or results of their work, I did key on one error in the write-up.

"All ’05 and later Twin Cams (except for ’08 FLH’s) come with a one piece 46 mm throttle body. "

Every 2005 (including my 2005 RG) I have ever worked on has the older 44mm Delphi system that has the separate intake & TB. The 46mm units started in 2006.

I dunno if (in)accurate documention means anything or not...???...

 

I wouldn't run an epoxied manifold on a street bike. Ever. Asking for trouble. I've flow tested & dyno tested the stocker, SE50 & the HPInc. 51 & IMO if you're looking for max power the HPInc. throttle bodies outperform the others hands down. For the guy that's looking for 100/100 the stocker is fine.The older 2 piece were much better performance wise than their replacement. But that's how it is with all things Harley. Even some of the SE stuff is made in asia.

 

I emailed them yesterday asking about their service, and they responded saying they couldn't do anything with my '05 setup. So I replied pointing out exactly what you quoted here..........should be interesting to see their response.

Steve