|
|
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 ’06 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.E.T. intake manifolds). After the manifold was epoxied and ported,
we tested it on the flow bench and it flowed a lot more with the epoxy,
257 CFM @28”. Now we were faced with a manifold that was about 15%
smaller, had the proper taper that an intake should have, and it flowed
14 more CFM (38 more CFM than stock!!!!) This could only mean
that the port velocity was much higher in the manifold with the epoxy.
So we took the 51mm High-Velocity throttle-body to the dyno.
Unfortunately, we were unable to retest the epoxied 51mm High-Velocity
throttle body on the same 103 cu” TC, so we took advantage of a
very mild 106 cu” TC with a very good baseline on it and a stock
throttle body. The 51mm epoxy unit was installed and properly tuned in.
This is where the results turned for the better… way better. SEE
DYNO
The HP went from 100 HP
to 107 HP and the torque went form 110 ftlbs to 115 ftlbs of torque. We
also noticed the power increases were produced throughout the entire RPM
range and not just in the higher RPM areas. These results were very encouraging
find and could only mean one thing; we accomplish our original goal.
As a result, Johnson Engine
Technology, Inc. can now offer a service that will take the stock throttle
body of a potential customer and modify it for optimum performance without
the high cost of the aftermarket part.
-Written By: Robert Johnson
J.E.T.
mod 48mm Hi-Flow Throttle-Body,
(06-present EFI, no 08 FLH):
169.95
J.E.T. mod 48mm Hi-Velocity Throttle Body,
(06-present EFI, no 08 FLH):
$365.95
J.E.T. mod 51mm Hi-Velocity Throttle Body,
(06-present EFI, no 08 FLH): $365.95
Email
us or call (401.596.9507) for more information or to order your modification
today. |
|
|
|
|
|
J.E.T.
Modified Stock Throttle Body: 51mm High-Velocity
Dear Robert:
I normally do not write Testimonials. In fact this is only the second
one in 30 years of street riding, but I am making an exception due to
the fact that I feel compelled to share my information not only to you
and your J.E.T. team but also to all of the Harley performance enthusiasts
out there that have simply burned their hard earned $ on performance upgrades
that do not work.
Robert, I appreciate your patience in answering all of my questions and
repeated phone calls. To say that I was skeptical at first would be an
understatement. You recommended that I go with your 51mm High-Velocity
upgrade which was actually cheaper than my original Screaming Eagle 50mm
purchase. You told me that it would “Rock-N-Roll”! I rolled
the dice.
J.E.T.’s 51mm High-velocity upgrade is the Real
Deal! I have a 2007 Roadking Classic with an Axtell 107CI
Mountain Motor kit, Redshift 577TC chain drive cams, Screaming Eagle 50mm
throttle body with larger injectors and a Thunderheader 2:1 system. Originally,
my numbers were a little low so I started searching for the bottleneck
that I believed was holding back the power on this 107CI Mountain Motor.
Unfortunately there has not been any data available for comparison until
now! Please
see my dyno chart.
Results are absolutely incredible! An increase
of 8.63 horsepower and 7.59 torque over the Screaming Eagle 50mm.
Even more impressive is the huge difference in real world riding and throttle
response with this upgrade. All of this has been achieved using stock
injectors. My fuel economy has improved even with aggressive riding. Talk
about having your cake and eat it too!
Special thanks go out to Angelica for her emails updating me on the process
of my throttle body upgrade.
Thank you Robert and all of the J.E.T. team for developing and producing
a product that is exceptional and a value in the Harley performance market.
Tony Johnson
Springfield, IL |
