North American Turbocoupe Organization



140 speedo problem
ratrapp Offline
Member
#1
we just installed a motorsport 140 speedo yesterday.it only has 16k miles on it.the speedo is 5 to 8 mph off for some reason.the needle doesn't shake or do crazy things,it's just off.i think i can change the speedo gear to make it pretty close but why should it be off in the first place?it reads slow,not fast.
88 turbo coupe ported e6 kirban afpr forge bpv walbro 255lph stinger3" dp into 2 1/2 duals ultra flows bobs gutted upper with 60mm tb ranger roller cam.t-3 race engineering cam pulley gillis vale k&n cone 3.73s centerforce d/f 140 motorsports speedo and fms rear spoiler 17x9 cobras
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bhazard Offline
Posting Freak
#2
You sure its a genuine Ford Motorsport one and not a converted one?
88 TC, 170k, K&N, $5 Boostvalve, Stinger 3" ex., 3" Magnaflow, 3" Stinger tail, Zoom clutch
15.26 @ 86mph, 2.18 60' killed valvetrain & headgasket
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Keith Nubel Offline
Posting Freak
#3
What rearend gear are you running?
1985 TC
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ratrapp Offline
Member
#4
yes,it's definitly a motorsports piece.the car is an 88 5spd. with the stock 3.55 gear.i thought there was someone on the board who calibrated the speedos.does anyone know who it was and if he still does them.
88 turbo coupe ported e6 kirban afpr forge bpv walbro 255lph stinger3" dp into 2 1/2 duals ultra flows bobs gutted upper with 60mm tb ranger roller cam.t-3 race engineering cam pulley gillis vale k&n cone 3.73s centerforce d/f 140 motorsports speedo and fms rear spoiler 17x9 cobras
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tps87turbo Offline
Posting Freak
#5
That would be Jeff K. He can calibrate it for you. I would send him an E-mail to ask how much & when it can be done.
Tony Sceia -

HIS Red 88 TC
http://turbotbird.com/showroom/data_r-z/...a_88tc.php
HERS - Blue 87 TC, fully loaded with every option, Work in Progress
87 Gray TC Parts Car - Gave to BJL and is now his daily driver
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Jeff K Offline
Administrator
#6
Yup, I am the one who does the calibrations. You can do it yourself also. Mike Walstead has instructions somewhere on the site for using the sound card in your PC as a signal generator to do the calibration.

I question: Is it off by a constant 5-8 mph, or does the accuracy change at different speeds, like it is accurate from 0-40, and then starts to read higher than actual speed as speed increases?

Most TC speedos, both the stock 85 and Motorsport 140 tend to read higher than actual as speeds increase.

One last question.... how are you checking the accuracy? I hope it isnt bases on indicated speed versus RPM compared to the old 85 mph speedo, as the original speedo is likely calibrated for crap in the first place.
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
11 Crown Vic Interceptor
14 Toyota Camry (wifes car)
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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Retired 56 Offline
Member
#7
Jeff, just a quick question. I'm converting a speedo to a 140 and was planning on checking accuracy with the tach verses 85 speedo trick. What is the best method for checking the accuracy? I'm planning on probably sending the speedo to you once it's put together but later on I plan to drop the tire size to a 225/16/50. What will that do to the accuracy of the speedo?
K&N cone, lowering springs urethane bushings subframe connectors, 255 pump, Spec stage 3, kevlar posi , 5 lug swap, Cobra 13"fr & 11.65 rear brakes
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Jeff K Offline
Administrator
#8
Best way to check the accuracy is with a signal generator with accurately known frequency output. The VSS puts out 8 pulses per revolution, and the VSS rotates at the industry standard of 1000 rev/mile (assuming speedo drive gears, etc are correct). The VSS puts out a sine wave like output. Doing the math gives 2.22 Hertz per mph. In other words, speedo should read 60 mph for 133 Hz input freq, 100 mpg for 222 Hx input, etc. I use a POS signal generator we were getting rid of at work, along with a Global Specialties 8 digit frequency counter to measure the actual freq output of the POS signal generator.

Of a fair number of stock 85 mph speedos I have checked before conversion to 140, I have found that they are often pretty accurate up to about 50 mph, but once over 60 mph, they read way high. Had one that read 67 mph when it should have read 60. Most read 64 or so at a real 60. Dont even ask how bad they are at 80 mph.

When I do the calibration, I can usually get them to within +/- 1 or 2 mph between 20 and 80 mph, but often they still read 5-7 mph high at 130 mph. I can either get the low speed region nearly dead on with the high speed region off, or the high speed region dead on with the low speed region off. That is just the nature of the way the calibration weights inside the meter movement work.
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
11 Crown Vic Interceptor
14 Toyota Camry (wifes car)
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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trashline Offline
Posting Freak
#9
haha so that would explain why I sat there and played with speedo gears for two months I go thru a radar station at 60 and it says 64 lol gesh what a crappy design. Time for a autometer and custom gauge install lol.
Brian

www.BCPCustom.com

06 Cobalt SS
66 mustang 289 C4 handfully modded

Stingers IC install and tbird photos
http://community.webshots.com/user/trashline
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ratrapp Offline
Member
#10
nope,i'm not basing it off the old speedo.it reads slower,not faster anyway.i'm basing it off my brother getting a ticket in it.it said 55-58 and he got 68mph.hopefully in like 2 or 3 weeks i'll be sending you a speedo to fix.thanks alot.
88 turbo coupe ported e6 kirban afpr forge bpv walbro 255lph stinger3" dp into 2 1/2 duals ultra flows bobs gutted upper with 60mm tb ranger roller cam.t-3 race engineering cam pulley gillis vale k&n cone 3.73s centerforce d/f 140 motorsports speedo and fms rear spoiler 17x9 cobras
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