My home made 140 MPH speedo

Spooler87: all the answers to your questions can be found on the Fox Thunderbirds link posted above.

In the next week I plan to have that article typed up, so if you can wait a little while there should be a nice, clean cut and easy to understand article with lots of pics for you to view on the Coolcats website.

Joe

[This message has been edited by joefriday (edited 12-19-2003).]

Thats cool. Thanks for all the work you have put into this. One small question though. did you have to cut out the individual hash marks on the white guage overlays? I just dont think that the dash lights would shine through if you didnt. Also, if you did cut them out, would they be visible during the day? I'm really interested in using the overlays for the stock speedo, while i try my hand at converting the spare I have. I'd really like to use the white overlays.

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87 Tubocoupe, Light Regatta Blue, All Options incl. Leather; 2.5" exaust, Dynamax super turbo mufflers w/3"chrome tips, MSD 6AL, Blaster2 Coil and wires, Homemade adjustable boost valve.

"May the fluids under the hoods of the beleivers flow forever"

For properly sizing the gauges I ended up pasting them in a Word .doc I can mail it to anyone who wants it.

steve

UPDATE: I pulled the cluster out of the car today. I checked the calibration on the 85 mph speedo that was in the car, and it was high. At an actual 60 mph (133 Hz signal in to speedo) it read 64 mph, which confirmed my suspisions that it always read high. At an actual 30 mph, it read 34. Only got accurate at 80 mph. So, I thought, WTF, change the cap in the old speedo to a 33 nF, put the 140 gauge face / clear/green plastic assy on the old speedo, and see how well it works. TO MY COMPLETE SURPRISE, calibration was MUCH MUCH better than it was with the other JY speedo I had tried the conversion on the first time. Very low speed calibration sucked (actual 20 mph indicated as 16 mph), but as speeds climbed, accuracy increased greatly. For example, actual 30 indicated 29, actual 40 indicated 39, from 50 to 75, accuracy was dead on, from 80 to 100, speedo indicated 2 mph high, and by 130, it was reading 5 mph high. MUCH better than the original speedo! This leads me to believe the meter movements in the speedos are cheap pieces of junk, and every one will turn out differently.

I put the original speedo that came out of the car (now calibrated for 140 mph) in the car, and went for a drive. WORKS GREAT! Seems to be very accurate!


Eric: I tried several different resistances from 470 ohm to 3300 ohm in series with the 33 nF cap, and none made any difference to the calibration at low or high speeds.

Spooler: Do not cut out the hash marks. As I mentioned above, I used heavy paper, sprayed on both sides with clear coat, and light comes thru just fine. A little dimmer than the tach, but not enough to really matter.

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Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 21 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)

Hey all, I thought I'd check out an extra 87 speedo I have for accuracy. Here is what I found using the freq generator before mod:
10mph (22.2Hz) = 9 indicated
20mph = 18
30 = 30
40 = 40
50 = 51
60 = 62.5
70 = 73
80 = 83
90 = 91
I'll post results after I do the mod.
After mod results:
(This was done leaving in the 100K resistor and installing the .033ufd cap)
20 = 19
40 = 40
60 = 62
80 = 87
90 = 98
Beyond this point, all readings were way high. Putting in the 110K resistor made this even worse. I went down to 92K and it read too low. I decided to try a 200K trim pot. It allowed tweaking and I was able to find a happy medium:
10 = 5
20 = 18
40 = 40
60 = 61
80 = 84
100 = 103
120 = 120
140 = 138

Since I'm too lazy to get out my DMM, I'm going to guess the final resistance of the trim post is around 98K. Just from the tests run on this thread, it's safe to assume that each speedo will be different and will require a specific resistance to read as accurately as possible. Thanks to all for the great ideas!

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www.stangnut.com
1988 Tcoupe
1984 20th Anniversary GT350 Mustang 'Vert
1984 Mustang GT T-roof
1965 Shelby Cobra Replica

[This message has been edited by fiveliter8 (edited 12-21-2003).]

Okay Jeff, I See your point. The heavy paper and not cutting the hash maks out would work with the Black faces, because the hash marks/numbers are white. Light would shine through them. But what about the White face overlays?? the numbers/hash marks are black.....meaning that light will not shine through them. or will it work as sort of a "Negative Effect" meaning that at night the entire face lights up, leaving the numbers black for visibility?

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87 Tubocoupe, Light Regatta Blue, All Options incl. Leather; 2.5" exaust, Dynamax super turbo mufflers w/3"chrome tips, MSD 6AL, Blaster2 Coil and wires, Homemade adjustable boost valve.

"May the fluids under the hoods of the beleivers flow forever"

I really dont know how well the white faces would work when lit up. Never tried it.

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Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 21 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)

Steve,I would LOVE to have them if you don't care to send them out to me...Here or [email protected] way is fine...thanks

Jeff

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86 T/C black with red leather interior,tinted windows,5 spd,3" exhaust,
dynomax dumped at the axle,lots of mods planned,gonna be a heck of a ride,hang on

I would be interested in buying the 140 and the 7k tach for the V8 inlays if someone can make them out of the plastic that they used in the factory ones.

James

Originally posted by teal95:
For properly sizing the gauges I ended up pasting them in a Word .doc I can mail it to anyone who wants it.

steve

I would LOVE to have it if you wouldn't mind. Thanks...

Jeff

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86 T/C black with red leather interior,tinted windows,5 spd,3" exhaust,
dynomax dumped at the axle,lots of mods planned,gonna be a heck of a ride,hang on