My home made 140 MPH speedo

With all the talk about 140 mph speedos lately, I thought I would make myself one. First, I take NO credit for any of these ideas. 100% of the credit goes to joefriday for figuring out the electronics, and Eric Dess for his high resolution jpeg images of the 140 speedo face. In all, it took me about 6 hours total to make it, and it cost me zero dollars to make, as I have a spare instrument cluster, and access to small electronis parts, namely the 33 nF capacitor needed to change the 85 mph unit to a 140 mph one.

I have access to more electroic test equipment than most people, so I thought I would check the calibration of the "new" speedo. The VSS puts out 8000 pulses per mile driven, and doing the math, this means every 2.222 Hertz signal to the speedo should be 1 mph (i.e., if speedo is driven with a 222Hz frequency, it should read 100 mph. I borrowed a signal generator and very accurate frequency meter from work to check the calibration. The first picture shows the speedo driven with a 267 Hz signal, and it indicates 120 mph, as it should. Second picture shows it driven by a 133 Hz signal, and it shows 60 mph, as it should. Here is the weird part.... from 55 mph on up, it is accutate to within about 1 or 2 mph. Below 50 mph, accuracy sucks.... an indicated 35 mph is really 40 mph, and an indicated 23 mph is really 30 mph. Very strange!

BTW, as long as pulse voltage to speedo is over .2V RMS, speedo will read correctly independant of pulse voltage. I tried sine waves, triangle waves and square waves, and all wave shapes gave the same speed indication.

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Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 20 psi, forced air intercooler, water injection, bypass valve, Ranger roller cam, subframes, etc., etc.. // 86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP nitrous, ignition, gears, suspension, etc., etc.... // 91 Escort: Bone stock winter car // 02 Taurus Vulcan(wifes car)

[This message has been edited by Jeff K (edited 12-18-2003).]

What, no instructions? Post it on the tech articles page!

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Ed Meinel
88 TC: stock
88 TC: twins!
99 Mustang GT vert: modded
www.turbotbird.com/showroom/EdMl_88TC.html

Does the capacitor replacement impact the odometer reading?

I'm looking forward to doing this, although the under 55 mph problem concerns me. Any ideas on why that is happening or how to correct?

This backs up what I found. It seems to be very inaccurate at low speeds, and since my daily commute now tops out at 55 I haven't had a chance to check it any higher. I was planning on borrowing a specialized GPS speed measurement device we have at work, but it is out for repair.

steve

Jack: Odometer is not affected by the change in speedo calibration, as the odo is driven by a stepper motor and is a completely seperate system. I did check odo calibration. I set drive freq. to 267 Hz (120 mph), zeroed trip odo, and ran it for exactly 10 minutes. Trip odo showed exactly 20.0 miles, as expected.

My spare cluster was pulled out of a running car that was rear ended / totaled, so I assume the speedo was originally working correctly. I could kick myself for not checking the calibration on the speedo before I modded it to the 140. To tell you the truth, I never really trusted my current 85 mph speedo anyway... always seemed to read a little high. When I get around to changing my current 85 to the new 140 (dont know when I will get to it... it is f***ing COLD here) I will check the calibration on the 85 mph unit.

Ed: If you want more info, see http://pub5.ezboard.com/ffoxthunderbirdsgeneralinform ationon19831988thunderbirdsandcougars.showMessage?topicID=1622.topic . Everything you need to build your own is there. I think joefriday, the guy who deserves the credit for this, is going to do a write up an post it on coolcats. If I write something up, I feel like I am steeling someone elses hard work.... remember I didnt do any of the development work on this, I just followed some instructons myself, with very little of my own innovation going into the project. I would feel like I was steeling intellectual property.... I think especially you can understand that.

One more thing on accuracy.... The accuracy specs on speedos in the Ford shop manuals are surprisingly loose. I forget the exact values off hand, but the spec is quoted only at 60 mph, and it is something like speedo is in spec if it reads anywhere from 57 to 65 mph at an actual speed of 60 mph.
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Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 20 psi, forced air intercooler, water injection, bypass valve, Ranger roller cam, subframes, etc., etc.. // 86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP nitrous, ignition, gears, suspension, etc., etc.... // 91 Escort: Bone stock winter car // 02 Taurus Vulcan(wifes car)

[This message has been edited by Jeff K (edited 12-18-2003).]

Good job, Jeff. Looks like you will be driving at 120mph, just to be accurate [Image: biggrin.gif]

My speedo over-reads by 10%, despite never changing the VSS gearing and using stock wheels and tires.

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86 TC, 73 Mini, 72 Mini Van project (w/ LS-1 motor)

Click here to beat a ricer.

I've found that a simple Garmin hand held GPS is great for checking the accuracy of a speedometer. They read to the tenth (.0) and respond very quickly to changes in speed. I found that my family truckster is off by 6% with larger tires and use that for mpg calculations.

Jeff:
Since you have everything needed to check the accuracy, can you find the correct points for the marks of the face? That seems to me like the easy way to correct for error. Maybe you or someone else can make a new JPG or PDF (personal preference).

Originally posted by TCorBUST:
tires and use that for mpg calculations.

Jeff:
Since you have everything needed to check the accuracy, can you find the correct points for the marks of the face? That seems to me like the easy way to correct for error. Maybe you or someone else can make a new JPG or PDF (personal preference).

I dont know shit about redoing jpegs, photoshop, or anything like that. I also suck at anything artistic. I did an Excel table and a few graphs of measured versus actual speed differences for my particular speedo. I will send you the Excel file if you want a copy of it. [email protected] (home) [email protected] (work)

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Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 20 psi, forced air intercooler, water injection, bypass valve, Ranger roller cam, subframes, etc., etc.. // 86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP nitrous, ignition, gears, suspension, etc., etc.... // 91 Escort: Bone stock winter car // 02 Taurus Vulcan(wifes car)

Jeff, if you wouldn't mind that file would be something we could throw in the article on COOL CATS. joefriday and I are in contact and as soon as his preliminary testing is also done, we're going to make an official page on the site so anyone can do it. Your electronic info is invaluable!

BTW, for everyone else, you can print your own speedo and instrument cluster faces via my site here: http://www.coolcats.net/media

I made a whole bunch of T-Bird logo faces for everyone. If you'd need something custom (logo, numbering, etc.) drop me a line ([email protected]) and I'll be happy to do that for ya.

So..do you think a 180mph speedo would be too much [Image: biggrin.gif]? I've got a canuck cluster which I'm going to have to have recalibrated (older style mechanical) for the 83 'Bird. I could have it set right as it sits for 180 km/h max (approx 112 mph) or I could maybe have them calibrate it so the km/h are instead mph [Image: tongue.gif]
I may just do another gauge face and have them do it for 150 mph.

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Any connection between your reality and mine is purely coincidental..
83 TC Clone, 87 Ranger (soon to be 2.3T), 84 XR7, 80 XR7, 86 XR4 and 62 Mercury Monterey
NATO Member