Speedometer calibrator for exact reading. | FerrariChat

Speedometer calibrator for exact reading.

Discussion in 'Technical Q&A' started by Paul_308, Jul 3, 2011.

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  1. Paul_308

    Paul_308 Formula 3

    Mar 12, 2004
    2,345
    #1 Paul_308, Jul 3, 2011
    Last edited: Jul 3, 2011
    My speedometer has always read 10% high, 60 indicated and 54 GPS. And that brings uncertainty on the interstate.

    A high-tech motorcycle aftermarket company named 12o'clock.com has speed correction modules for bike users who change gear ratios, greatly messing up the speedometer readings. Their motorcycle correction module is an ideal solution for the Ferrari whose Veglia electricals match those on many motorcycles. I've already paid $200 to California while attempting to maintain a legal speed. I had planned to send my speedo to PaloAltoSpeedometer but hesitated. So I jumped at paying only $100 to have a speedometer I can believe in. FChat's jim94-348 has already installed one in his 348...his installation details: http://www.ferrarichat.com/forum/showthread.php?t=303123&page=2. Since this solution also works well in my 1980 car, it follows the GT4s, Mondials, and 328 are also suitable for the fix. It doesn't matter what the dial says, this unit can add or subtract pulses to make a percentage correction to any units. It can also be used to change kpm to mph if desired when you cross the border.

    The product is called 'SpeedoDRD model M'. An electrical buffer must be added to match the signal levels to/from the Ferrari circuit. 12oclock suitably calls this buffer the 'FBUF' and packages them wired together (middle below) with a cable. I chose to add a 4 pin connector such as the smaller Molex from Radio Shack so the unit can be removed or installed easily. The cable with female side of the 4 pin connector (just below right) is wired into the car power and ground. The signals wires (blue and white wires with connectors (photo just below right...left side of that photo) plug into the connectors shown bottom right.
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    Finding the connector
    Next step is to intercept the car's speedometer signal from the impulse generator and provide the path to insert a corrected signal. The existing path is a red wire with black tracer (red/black). I chose to gain access to my speedometer circuit wiring underneath the dash rather than removing the guages. Just above the driver's right knee are three similar large 8 pin connectors, which join body wiring up to the instrument cluster. The proper connector has not one but two red/black wires. One of the red/black wire candidates is for the fuel tank 'low gas' warning light. The other red/black wire is from the impulse generator supplying speed signal to the speedometer. A few simple tests will confirm which wire to cut, and install crimp connectors. By using a mating connector in this way, the entire setup can be removed in seconds and original function returned if need be.
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    Finding the wire in the connector
    You will discover there are two look-alike red/black wires in the same connector, so a test for the correct wire is imperative. The red/black we are NOT interested in goes to the gas tank low reserve switch and does have voltage from the lamp on the gauge side of the connector with the ignition switch on. Separate male/female of the proper connector for direct access to the male terminals (male=car body wires and female=instrument wires). Place a Voltmeter on the male terminal of the suspect red/black wire. Turn the ignition key on off on off. The correct wire will have +12v which is furnished by the impulse generator. The incorrect wire should have +12v on the female side which goes to the fuel tank. But with connector apart nothing on the male side. Another test for the wrong wire fuel tank red/black wire, can be done using an ohmmeter on the male side. That wire will read no continuity to ground until you short the red/black wire at the fuel tank to ground. It's an easy test for confirmation, done with ignition off and car battery disconnected. The proper wire on my car is shown at the inset drawing. Before cutting any wires, be certain you cut the correct one. Then add male/female connector to the ends. These will go to the calibrator but can also be used to re-establish original wiring of the car should you remove the calibrator.
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    OTHER CARS: GT4s have an 18 pin connector to the instruments rather than three 8 pin connectors but still do use a red/black wire for the speedometer. All 308s from the earliest carb to the 1989 QV use same 3 large connectors. 328 cars should be easier as F changed the 'low fuel' indicator wire color to grey so there is only one red/black wire at the connector. But there is a red wire so confirm the identity of the proper red/black by the black tracer color. Alternatively one can remove the instruments and access directly to the rear of the speedometer, the '-' terminal. 348s, check the link above for specifics.

    Power and ground must be located and wired to the harness. Power must be ignition key switched which is available at the fuse panel in many spots. A test light will prove this and find the easiest for you. I happen to have switched +12v near the lamp socket used for turning parking lights on/off with pods down, so I used that. Ground might be the most difficult but there are screws holding the fuse/relay panel to the car and are great for a solder lug.

    A word about programming. I suggest playing with the unit in the comfort of your favorite chair before installing int he car by connecting the power and ground to a small 12v battery, rather than doing it in your car. Thoroughly read the tiny-print manual (I reprinted it much larger). It takes some time to become familiar with the menu system and nano sized switch. Basically, setup is done by pressing a pinhead sized microswitch with your thumb nail while observing red-green led lights and releasing the switch after the proper lights have blinked in the desired sequence. That nano-switch is visible in the upper left photo just above the IC. Soon you will become familiar with the quick led sequences and how to insert menu commands and interpret results.

    I programmed my unit for a simple -10% correction and took the car out for a test. Voila, agreement with the GPS for the first time. Guess I could tweak further for -9.73% but don't think the difference would be noted.
    Ordering information = Brooks @ 12oClockLabs (937) 719-1518 mention my name
     
  2. ramosel

    ramosel Formula 3

    Sep 11, 2004
    1,237
    Meadow Vista, CA
    Full Name:
    R Moseley
    #2 ramosel, Jul 4, 2011
    Paul,
    As usual from you... an elegant solution to a common problem. I'll order mine this week.

    Rick
     
  3. Ferraripilot

    Ferraripilot F1 World Champ
    Owner Project Master

    May 10, 2006
    17,186
    Atlanta
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    John!
    #3 Ferraripilot, Jul 4, 2011
    This is absolutely fabulous. I notice these speedos are correct up to about 45-50mph and then they begin reading high. Is this a correction that is a flat 10% change or is it able to work at certain speeds and above? For example, at 55mph on the speedo I am really going 51mph, but a showing of 85mph on the speedo is an actual 77mph, and for academic purposes only 155mph showing is an actual 143mph. See what I mean? It's 8% in some areas and then the scale becomes larger the higher/faster you go.
     
  4. Paul_308

    Paul_308 Formula 3

    Mar 12, 2004
    2,345
    #4 Paul_308, Jul 4, 2011
    The DRD correction is a flat n% across the entire range. Since my speedo was off the same amount at town speeds as highway speeds as best noted by the GPS, I am pleased with the results. The impulse generator is fixed to wheel rotation. The speedo is a d'arsonval meter which has a reputed 3% readout accuracy. But linearity of the SAY115 IC circuit is an unknown to me, and further correction against speed might be needed. Certainly, providing an variable error curve is possible in electronics just as an ignition ECU can provide more than a vacuum advance curve for spark. Getting the actual speed data vs speedo results at all speeds would be the next step.
     
  5. jim94-348

    jim94-348 Formula Junior
    Owner Silver Subscribed

    Aug 19, 2010
    971
    Greenville, NC
    Full Name:
    Jim
    #5 jim94-348, Jul 6, 2011
    Last edited: Jul 6, 2011
    I think I would recommend that you use a GPS and check your speeds a little closer. I think you will find that it should be linear. At slower speeds the 8% is much less noticeable. From the way the sending unit to the speedometer works it should be linear. When I first started looking for something to correct this I thought the same thing. After checking it mine was also 8% off but it was linear.
     
  6. Crowndog

    Crowndog F1 Veteran

    Jul 16, 2011
    7,042
    Fairfield,Pa
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    Robert
    #6 Crowndog, Sep 6, 2011
    Great thread. Just ordered up the set.
     
  7. Jdubbya

    Jdubbya The $10 Trillion Man
    Silver Subscribed

    Dec 28, 2003
    37,453
    PNW
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    John
    #7 Jdubbya, Sep 6, 2011
    I've checked mine with GPS several times and it's about as close to exact at 60 as I could tell. I haven't checked it at higher speeds though.
     
  8. FerrariDublin

    FerrariDublin F1 Rookie

    Jun 14, 2009
    3,452
    Dublin, Ireland
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    Greg
    #8 FerrariDublin, Sep 7, 2011
    Great write-up Paul - thanks for sharing with the community.
     
  9. ProRallyCodriver

    ProRallyCodriver Formula 3

    Oct 25, 2005
    1,250
    Alexandria, VA
    Full Name:
    Dave Shindle
    #9 ProRallyCodriver, Sep 7, 2011
    Last edited: Sep 7, 2011
    Most modern car's odos read high. I install highly calibrated rally computers into rental cars to make computer-generated rally pacenotes (stagenotes) for rallyracing events. Can't think of any model car I've rented that the speedo was not high.

    Another option is to install a rally computer in your car. With a rally computer you can calibrate its speedo/odo at any moment to adjust for things like changing tire sizes (summers/winters) or crossing border from miles to kms. You can also move it from car to car easily so one could serve your whole fleet. Most are too sophisticated and bulky for what non-rally people but there are some simple smaller units like the Coralba C-Mini.

    http://www.jemba.se/

    Most will have a program to tell top speed traveled. Neat thing to know for rally to and to compare w/ other rally teams. But friend who has one in his streetcar, he uses to see how fast his teenager has gone each time the kid borrows the car.

    Anybody interested, PM more for more details and I'll share US and Canadian dealers. Any readers in Sweden/Findland, the link above is the best Scandinavian dealer.
     
  10. Crowndog

    Crowndog F1 Veteran

    Jul 16, 2011
    7,042
    Fairfield,Pa
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    Robert
    #10 Crowndog, Sep 7, 2011
    Paul_308; what chip in the speedo goes bad and is hard to source? is it the say115y?
     
  11. dakharris

    dakharris Two Time F1 World Champ

    Jun 7, 2001
    29,441
    Sleepy Hollow
    Full Name:
    Cavaliere Senzatesta
    #11 dakharris, Sep 7, 2011
    Not sure how you get a ticket if your speedometer is reading faster than actual speed, but thanks for posting. Setting your speedometer 10% over is like setting your watch 10 minutes ahead so that you won't be late. Kind of silly. Many believe that Ferrari sets the speedo to read high to make owners think the car is faster than it is. Others believe that the odometer running faster makes the car escape warranty sooner. Maybe it's both?
     
  12. jm3

    jm3 F1 Rookie

    Oct 3, 2002
    4,364
    United States
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    JM3
    #12 jm3, Sep 7, 2011
    My speedo had to go to Palo Alto speedometer, and came back with an butt-ugly solder job of an FET on the side of the thing.

    Nobody has mentioned odometer.

    When I tested a different Ferrari, the speedo was almost exactly 10% over, but the odometer was dead nuts.

    The odometer, when the last digit was centered on the viewing window, was within the accuracy of the GPS, maybe one meter.
     
  13. ProRallyCodriver

    ProRallyCodriver Formula 3

    Oct 25, 2005
    1,250
    Alexandria, VA
    Full Name:
    Dave Shindle
    #13 ProRallyCodriver, Sep 7, 2011
    Hey you goodie-goodies in hammer lane thinking you are driving speed limit, move to the granny lane and let me by you. Sad to think so many people believe their speedos and are driving too slow.

    Rally computer is an odo, speedo & clock. You won't find a more precise method for the speedo or odo. Here is a better link to a C-Mini. You can see it is displaying thousands of whatever measurement its calibrated for.

    http://www.coralba.se/rally/readone.php?categoryID=15&id=10

    You calibrate rally odo yourself after driving short measured distance. Its so precise, I will have a calibration for each type of tire we use for transit regular driving and another for racing to account for wheel spin.
     
  14. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    9,268
    #14 Mitch Alsup, Sep 7, 2011
    I plop a GPS on the dash and use its MPH readout to compare with speedo.

    I'm running 275/40 tires instead of 265/40 tires on the rear and my speedo is only about 1 MPH off GPS at 70 MPH. Perhaps the 0.2 inches of additional tire rolling radius has something to do wiht it being accurate.
     
  15. gerritv

    gerritv Formula 3

    Jun 18, 2001
    1,400
    St Catharines
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    Gerrit
    #15 gerritv, Sep 8, 2011
    Yes, the older 308's use the say115y (do not install the say115x, your odometer will read exactly 50% of real).
    The odometer is dead accurate because it works off pulses. The speedomter is not accurate nor linear due to several factors. There is a mechanical adjustment on the speedometer meter to compensate for linearity but it doesn't always work. If someone/some company has 'been in there' it is very possible/likely that the wrong spec components were installed. E.g. different types of capacitors have various temperature curves, etc.
    The SAY115Y can be very difficult to find, although searching today popped up quite a few resources. Several years ago there was only 1! Just use Google and search for SAY115Y. An example price is 89Euro.
    If you search the forums here for my name and 'sound card' you should find instructions on using the sound output from a PC to calibrate the speedometer.
    The carb'd cars use 4 p/rev, the injected cars use 8p/rev of the sensor, this is why you can't swap speedometers between the 2 types.

    Gerrit
    http://dino308gt4.com
     
  16. gerritv

    gerritv Formula 3

    Jun 18, 2001
    1,400
    St Catharines
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    Gerrit
    #16 gerritv, Sep 8, 2011
  17. Carbuilder

    Carbuilder Formula Junior

    Aug 18, 2012
    550
    Bolton, ON
    Full Name:
    Rick
    #17 Carbuilder, Sep 4, 2013
    Reviving this old thread for those that haven't seen it, but have speedometers that aren't accurate. I just installed one of those gizmos (or is it a doodad?) and it works fantastic!

    My speedo was indicating about 10% too high. Now it is dead-on. The unit is really tiny and is fairly easy to install. Since I tapped the signal wires from the speedo, I also tapped the power and ground wires from it, so the added wiring is all in one place. The unit is tucked up with the dash wiring so nothing shows. Excellent product and great write-up!

    Rick
     
  18. Mozella

    Mozella Formula Junior

    Mar 24, 2013
    905
    Piemonte, Italia
    #18 Mozella, Sep 4, 2013
    My wife and I used to do a lot of TSD rally competition (not rally-racing) on a national basis (in the U.S.). We had one correction factor for pavement and one for unpaved roads. We also used a different factor when she drove as opposed to when I drove owing to the slightly different way we negotiated corners. Really good teams could score a 6 second cumulative error on 20 stages averaging roughly 18 minutes per stage, but the actual stage length could range anywhere between one minute up to 45 minutes. That means the error, on average, was less than one and a half seconds when entering 6 of the check points and less than a half second on all the other check points; pretty impressive driving/navigating. I was happy with less than a couple of minutes error on the day. Unfortunately the computer was pretty bulky and not something I would want in my Ferrari just for fun.
     
  19. robertgarven

    robertgarven F1 Veteran
    Owner

    Feb 24, 2002
    5,269
    Ventura, California
    Full Name:
    Robert Garven
    #19 robertgarven, Mar 30, 2018
    Friends,

    I downloaded a apple app for my iPhone called speed box. I propped it up in the window of my Euro GT4 and will write down the most common speeds as its in KPH only. I know the program is very accurate as I used it my other cars and it is spot on. The app even has a reverse feature so you can lay it on your dash and in the right light or at night it reflects in the window as a heads up display. My speedometer was off 18mph or 30kph at 65! It will be easier remembering the key speeds than worrying about it! Plus he speedometer is more accurate than the lighting at night is for my gauges! Ha Great thread though!
     

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