Turning It Up a Notch! - ATRA

LET’S PLAY BALL
Turning It Up
a Notch!
In the countless seminars, bulletins
and articles from the ATRA technical
department, the question
always comes up: “How much does it
increase when I turn it up?” No, not the
radio: the EPC solenoid.
Recently, Irvin Gers from APD and
I were discussing the difference
between the old and new Ford EPC
solenoids. Turns out they’re interchangeable,
but I took it a bit further. In
this issue of Let’s Play Ball we’re going
to lace up the pads and throw the ball
downfield for an EPC touchdown!
22 GEARS November 2002
D A Y & N I G H T
60
HOT OFF COOL
Okay, so what do you want your car
to do again? Are you sure you want the
tires to break loose at 55 MPH? There
are many, many modifications that will
do just that. Some of the top names in
the business have gone into overtime
researching the specific spring weights
and bore sizes to keep those hotrods
free of problems.
But what about the weekend warrior,
who can’t afford to bark the tires
with the wife and kids in the back… the
one who wants to race on Saturday, and
Sunday he’s plopped in front of the TV
70
80
by Lance Wiggins
watching every football game available?
Or what about the average Joe,
who just wants a little more uummph!
when the trans shifts? Try turning up
the EPC pressure.
Let’s take a look at what happens
when we turn it up: We’ll look at the
EPC solenoid from a Ford 4R70W.
There are two solenoids available for
this unit: The original one, and a new
one that Ford released. The first question
that usually comes up is: Will the
two solenoids interchange? Yes, they
will. Both solenoids have 4.5 ohms of

We performed these tests
on a 2000 Ford F150 and
a 1999 Lincoln Navigator;
both vehicles with
less then 50k miles.
resistance at room temperature, and the pressure ranges are
very similar, as you’ll see by the results. We performed these
tests on a 2000 Ford F150 and a 1999 Lincoln Navigator;
both vehicles with less then 50k miles.
The first graph (figure 1) indicates an early (F8 part
number) solenoid operating at the normal factory setting.
Notice the pressures on the right and the current flow in
amps at the top of the chart; these are going to be our indicators
for comparison.
The EPC pressure and amperage are inversely proportional;
that is, the higher the current flow, the lower the pressure,
and the lower the current flow, the higher the pressure.
Because the solenoid is normally open, energizing the solenoid
closes it. As the current varies, the pressure adjusts
accordingly.
When we turned the solenoid screw a quarter turn in
(clockwise), we noticed a slight but effective change. Look
at both of the graphs closely (figure 2). Both idle and
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GEARS November 2002 23

Turning It Up a Notch!
EPC SOLENOID
1/2 Turn
part-throttle pressures increase slightly
from the factory setting. This is just
enough to make those shifts feel right
on the money, on a unit with normal
wear.
Next, we cranked the screw in
another quarter turn, for a total of a half
turn clockwise. This is where your neck
starts to snap back, and the pressure
climbs to where it’ll bark the tires if you
have the horses to push it. As the graph
shows (figure 3), the pressure is significantly
higher and increases much
faster than the two previous graphs.
Comparing the pressures through
the EPC is good, but comparing mainline
response will really get your heart
pounding. With the adjustment set at
factory specs, mainline pressures were
between 60 and 70 PSI at idle, with
EPC pressure at minimum 0.0 PSI. As
throttle and torque increased, the pressure
rose to 170 PSI, and finally to
about 200 PSI at WOT.
When we turned the pressure up a
TURN IT UP!
1/4 Turn
Figure 3
quarter turn, idle pressure was at 90
PSI, with a WOT at 230 PSI. At half a
turn in, idle pressure was at 105 PSI,
and WOT at 240 PSI. As exciting as the
pressure change was, what’s really
exciting was how much faster the pressures
increased, and the response of the
clutch application. This is the touchdown
throw, and the celebration in the
endzone.
So far we’ve been looking at only
the early solenoid; the late model didn’t
perform as well as the earlier solenoid.
With a much faster response time and
higher pressures to boot, the earlier
EPC solenoid looks to be the solenoid
of choice. As for the comparison (figures
4 and 5) the black line indicates the
response at the factory setting; red is
the response with the screw turned in a
quarter turn; blue is the response at a
half-turn in.
The post-game stats show that
turning up the EPC solenoid is okay,
provided the rest of the unit is tight. But
Figure 4
Figure 5
The black line indicates the
response at the factory setting;
red is the response
with the screw turned in a
quarter turn; blue is the
response at a half-turn in.
don’t get careless: Any excess wear in
the valve bores or clutches are a sure
way to fumble the ball. Not only will
these conditions cost you time and
money, but they may also cost you your
customer. And, in general, you’ll want
to stay with a quarter turn for your regular
customers; half a turn for the customer
who wants to chirp the tires.
Anything more than that is just asking
for a penalty on the play.
So the next time you get a 4R70W
in the shop, don’t be afraid to turn it up
a notch. It’ll make those shifts a little
bit better, and make your customers
really stand up and cheer! And that’s the
Game...
24 GEARS November 2002

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