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DMP Speedcal Install
Cruise control, odometer, driveability, traffic tickets,
insurance rates... What do all those things have in common? All
of them are affected by the accuracy (or lack thereof) of your Vehicle Speed
Sensor (VSS). The vehicle speed sensor informs the computer of your
speed and also computates your mileage. If it’s wrong, you get a wrong
speedometer reading and rack up mileage that you never drove reducing the
value of your car. If you have changed gears or tire sizes, your
VSS is not reading accurately. While the common remedy for correcting
the VSS with a different Speedo gear can work (depending on gear and tire
size) but they are never perfect, most vary about 4% up or down from actual
speed and that's only if they make a gear that matches your needs, sometimes
getting a gear to work well means opening the transmission to change the
drive gear. Not only is calibration a factor, but also if you have
for example 4.30 gears on a 98 Cobra like I do, there are no real options
out there. The speedo gears become so small that they strip after a
few thousand miles and you gotta keep replacing them.
Up until recently, there was only 1 other way of correcting your speedometer,
using a gearbox that is calibrated for your existing combo. These are
expensive and cannot be adjusted if you change anything. I have used
both these methods and they were not satisfactory. The speedo gear
change method had my gear chewed up in less than 2000 miles, the gearbox
method only worked for the tires and gears that I chose at the time that
I ordered. When I changed gears, there went the 200 dollars for that
gearbox.
After changing gears and tire size again late last year, I was looking for
a better option; I would be changing gears and tire size in the future especially
when racing. On the street I use 245/45/17 Nitto Drag radials and when
racing I use 28x12.5x15 Mickey Thompson ET STREETS. The Nitto’s measure
25.7” diameter and the MT’s measure 28” so there would be a huge difference
in calibration between the two tire sizes. I did not want to be climbing
under the car and swapping out speedo gears, or buying two different gear
boxes at 200 dollars a piece just so I wont be racking up the wrong mileage,
or getting a ticket when the speedo says I’m doing 50mph and I’m really doing
80mph. When I first started modding my Cobra, there were only the mechanical
options and they were not acceptable to me. I did some asking around
and was told to look into the Dallas Mustang Speedcal, it was supposed to
be the latest solution to an age-old problem.
The Speedcal is an electronic box that is infinitely and easily adjustable
for any combination of gear ratio and tire size you can imagine. It
is programmed by setting the 10 dipswitches in the appropriate manner for
your car’s combination and is very easy to do without getting your hands
dirty. The Speedcal mounts inside the passenger compartment underneath
your center console. To adjust the Speedcal, you just pop off the shifter
bezel on the console and the box is staring you in the face. Pull it
out and remove the four screws holding the back plate on the box and set
the dipswitches. To get the proper settings, all you need to do is
direct your internet browser to the DMP website and they have a nifty calculator
where you input your cars gear ratio, tire size, and speedo gear tooth count.
It does the math and tells you the setting. The settings are in binary,
1 or 0 where 1 is ON and 0 is OFF. My settings for my 4.30-geared car
with a stock 19 tooth speedo gear and 245/45/17 tires were 1010100001.
When I switch to my 28” tall Mickey Thompson tires I would use 1001101010.
The programming takes less than 5 minutes and will be dead accurate.
Opening up the box
Upon opening the box, you will find the Speedcal unit, a connector housing,
and a scotch lock splice connector, and some very detailed instructions.
The Speedcal unit has 1 red wire (power), 2 wires installed into a connector
housing, and 2 wires that are hanging freely. This is all there is
to the unit, it’s a very simple piece and makes installation go very smooth.
Installation
The first thing you will notice in this article is there are no pictures,
not that I don’t own a camera but felt there was no need to shoot any pictures.
The instructions were very well written and needs no additional clarification,
which is very rare these days. I had absolutely no trouble with this
installation and just for the record, I HATE WIRES! I hate crimping,
cutting, measuring, taping, everything electrical (except soldering, melting
metal is just plain COOL!) but this install was VERY EASY. I can’t
stress that enough, not only did the instructions tell you what wires go
where, but even the color code of the wires for both 96-98 and 99 through
current cars. Most instructions say to install the power wire to a
“12volt power source”; well this is too generic a description for guys like
me. I like to know color codes and locations of wires and the Speedcal
instructions did just that. Again, I don’t have pictures of the install
because I felt it wasn’t needed since the instructions were so good.
I will break it down a little just to satisfy your curiosity. After
setting the Speedcal dipswitches to its proper setting, follow these instructions.
Step 1. Disconnect the vehicles battery
Step 2. Remove the shifter knob
Step 3. Remove the shifter bezel by pulling up on the
edges, they just snap in place so just pull straight up. Remove the
bezel and shifter boot and disconnect the wires going to your lighter.
Step 4. Remove the 4 8mm bolts that hold on the lower
shift boot.
Step 5. Place the Speedcal box in front of the shifter.
Step 6. Drop the wiring down the drivers side of the transmission
leaving the red wire inside the car, you will install this wire to the correct
12v + wire noted in the instruction manual.
Step 7. Re-install the lower boot, shifter bezel and shift
knob. All the in-car work is now done.
Step 8. Underneath the car, remove the VSS connector and following
the instructions remove the two wires from the connector
Step 9. Install the two wires from the Speedcal into the
VSS connector you removed in the previous step and re-install the connector,
which is now hooked up to the Speedcal onto the VSS sensor.
Step 10. Take the two wires you removed from the VSS sensor
and install them into the supplied connector housing. You will need
to match one of the wires to coincide with the gray wire on the Speedcal
connector.
Step 11. Attach the connector you just assembled to the
remaining connector in the Speedcal wiring harness.
Step 12. Tie up the wires out of the way of any moving
parts.
Step 13. Reconnect the battery
The whole install takes less than 30 minutes and now you are ready to test
drive your car, if the speedo moves the unit is working.
Final Conclusion and Testing
After installation and test-driving, I did some other testing on my own to
test the accuracy of the unit. I hooked up my laptop to the transmission
computer in my car. I have a Baumann Engineering Baumannator transmission
controller that I use to program the 4R70W transmission in my car.
One of its features is a dashboard monitor that will tell you the exact speed
of your car based on the Output shaft sensor on the transmission. You
input the tire size and gear ratio and it does the calculations in real time.
I did some steady state cruises at different speeds and compared my speedometer
to the Baumannator digital speed readings; they were EXACTLY the same at
all speeds. Very impressive. One important piece of information
I should clarify here is that this unit is designed only for 1996-1998 Automatic
Transmission cars and all Manual transmission cars. The reason for
this is because of the electronically controlled transmissions the late model
99-present cars use. The shifting is controlled by the computer, which
uses the Output Shaft Sensor to compute speed, like my Baumannator.
If you change gears or tire sizes with these cars, the transmission will
shift improperly and only a computer re-flash or aftermarket “chip” can fix
this. While the Speedcal will work on the automatic cars to correct
the VSS, the chip needed to fix shift points can also be calibrated for the
correct gear size so the Speedcal would be redundant. Willie Norman,
and the guys at DMP know this and will recommend that you fix the speedometer
with a chip instead of the Speedcal unit to save you some money. Nice
guys. According to Norman, who does not actually work for DMP but is
instead an independent contractor whose main line of work is in the Aerospace/Defense
industry and designed the box to help support his car habit, the latest version
of the Speedcal will now be a universal unit that has another bank of dipswitches
for input and output and can accommodate any electronic VSS known to mankind.
The Speedcal is not the only system of this type on the market; there is
the old Abbot ERA unit that has been around for a couple of years.
Willie Norman, the designer of the Speedcal saw that the ERA box could be
improved, so he designed his unit with some improvements. According
to Willie “On the technology we use, actually it
doesn’t have a microprocessor. I designed a custom logic circuit that resides
within the big black chip, which is a Field Programmable Gate Array. One
of
the input words actually has MORE bits than 16 bits to insure we have enough
resolution on the data.” OK, now I have no idea what that means but
it sure sounds good. Maybe some of you guys can figure it out, all
I know is the thing works and it works well. The problem with the ERA
unit is that your cruise control also uses the VSS input and many found out
the hard way that the cruise control will have stuttering/Surging problems
with the ERA box; the Speedcal does not have this problem and works flawlessly.
Now the final and all-important question, how much does it cost? From
DMP the unit costs $99.95. I believe Brothers Performance, a.k.a. BBK
also sells the unit, but I’m not sure of the price. If you have a car
that needs one of these boxes, you cannot go wrong with this unit.
You might be asking yourself why you need a box like this, but from personal
experience I can tell you it is a good investment. Speeding tickets,
“ghost” mileage, and just the peace of mind knowing your car is functioning
as intended is reason enough to buy this unit for your car. The mechanical
ways are outdated and more expensive than this unit and will save you from
having to get back under the car for another gear swap session, that’s what
I personally like the most and the fact that electronics are cool, even if
they do use some wires.
For more information, contact Dallas Mustang Parts or visit their website
at www.dallasmustang.com.
If you would like to see the page for calibrating the Speedcal, goto http://www.dallasmustang.com/speedcal.htm
and to see the real instructions online that actually show some pictures,
goto http://www.dallasmustang.com/speedcal_instructions.htm.
If you have any questions, like always, just drop me an email at jadkins@superstallions.com
and I’ll be glad to help you out in any way that I can.
Be cool guys,
James Adkins
IslandVobra
SSOTN Pacific Islands Coordinator and Staff
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