145 mph speedometer (Page 1/1)
jonrev SEP 10, 01:34 AM
Found this low-mile '85 GT, anyone know where the 145mph speedo came from? I assume it's a modified metric speedo but the 145mph readout (versus 140 like the IRM conversion kit) and non-matching font are throwing me off.
hyperv6 SEP 10, 06:27 AM
Not sure as I have never seen this one, I wager a conversion of some kind.

I have a metric but it does not look like this, I also have the Fiero club conversion and it goes to 200 MPH in case you drive off a cliff.

Back in the day there were several conversions and this may be one of the more rare ones,
Dennis LaGrua SEP 10, 09:02 AM
Only one forum member Scott (Darkhorizon) has ever gone the quarter mile at 142 miles per hour in a Fiero with a 9.42 ET so he might need it.. The person who did this conversion was very optimistic and my guess the unit may have come from another vehicle..

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

82-T/A [At Work] SEP 10, 09:51 AM
In my less responsible days... my 87 Fiero in good service, aftermarket exhaust, hogged manifolds, and K&N air filter, would exceede 120 miles an hour. It would actually go well past... probably closer to 130 miles an hour. And then it just kind of... stopped accelerating. I don't know what this is called, but I assume it's where horsepower and co-efficient of drag and resistance on the road hit a wall... and the car just wouldn't accelerate any further. I still had another 400 of usable RPM before it got into the red.

This was with a GX3, 3.33:1 final drive Th-125c. The car ran really well... to be clear, and I had a ThermoMaster chip on it (which who knows what it even does). If I had to guess, I was probably doing around ~128 miles per hour.

Totally irresponsible. I was 19.


I think I remember seeing that speedometer in the Big Fiero Parts Book from back in the day.
1985 Fiero GT SEP 10, 10:29 AM

quote
Originally posted by 82-T/A [At Work]:

In my less responsible days... my 87 Fiero in good service, aftermarket exhaust, hogged manifolds, and K&N air filter, would exceede 120 miles an hour. It would actually go well past... probably closer to 130 miles an hour. And then it just kind of... stopped accelerating. I don't know what this is called, but I assume it's where horsepower and co-efficient of drag and resistance on the road hit a wall... and the car just wouldn't accelerate any further. I still had another 400 of usable RPM before it got into the red.

This was with a GX3, 3.33:1 final drive Th-125c. The car ran really well... to be clear, and I had a ThermoMaster chip on it (which who knows what it even does). If I had to guess, I was probably doing around ~128 miles per hour.

Totally irresponsible. I was 19.


I think I remember seeing that speedometer in the Big Fiero Parts Book from back in the day.



And I've gotten to 138mph at 10 out of 14psi and 75% throttle, 3.4 turbo, f23, only stopped accelerating because that's when the headlights popped up! That's with the 140km/h speedo, it was doing loops for a little while haha, real speed was logged with the megasquirt ECM, then verified based on transmission ratios and rpm. As for responsibility, this was on a closed taxiway (old, long closed Loring air force base, there was an event there, and I got to accelerate down the 1.5 mile long taxiway). I certainly don't do that on the roads haha. 1/4 mile speed doesn't dictate total top speed, so it's believable that that speedometer could have a use on some modded Fieros, although top speed tests are a lot less common and accessable than the quarter mile.

[This message has been edited by 1985 Fiero GT (edited 09-10-2025).]

82-T/A [At Work] SEP 10, 11:31 AM

quote
Originally posted by 1985 Fiero GT:


And I've gotten to 138mph at 10 out of 14psi and 75% throttle, 3.4 turbo, f23, only stopped accelerating because that's when the headlights popped up! That's with the 140km/h speedo, it was doing loops for a little while haha, real speed was logged with the megasquirt ECM, then verified based on transmission ratios and rpm. As for responsibility, this was on a closed taxiway (old, long closed Loring air force base, there was an event there, and I got to accelerate down the 1.5 mile long taxiway). I certainly don't do that on the roads haha. 1/4 mile speed doesn't dictate total top speed, so it's believable that that speedometer could have a use on some modded Fieros, although top speed tests are a lot less common and accessable than the quarter mile.





Yeah, for me... the pedal was floored. I was WOT at ~128 miles an hour, and just not accelerating any more. It was a weird feeling. But yes... totally dumb and irresponsible, but again, I was 19... so I've changed a lot since then.

Kind of funny, but before I put my Fiero away into storage, like 15 years ago... I installed a Canadian equivalent to the 120mph speedometer. A lot of Canadians live in South Florida during the winter, and sometimes their cars call it quits when they're down here... so they end up in the yard. I saw dozens of Canadian cars down here (some I'd never seen before), but a lot of Canadian Fieros too... so these were plentiful at the time.




I installed it because I thought it made my car look cooler and faster, haha... of course... it's less than 120mph... but at least it still has the 120mph in small numbers. I swapped out the motor that runs the odometer with the metric one.

That 3.4 sounds awesome though...

css9450 SEP 10, 01:26 PM

quote
Originally posted by 82-T/A [At Work]:

I installed it because I thought it made my car look cooler and faster, haha... of course... it's less than 120mph... but at least it still has the 120mph in small numbers. I swapped out the motor that runs the odometer with the metric one.




Did you ever swap temp gauges? That one reads temp in Celsius.
hyperv6 SEP 10, 04:42 PM
I have the 180 KM GT dash in storage, Found it in the junk yard.

The early cars were all 85 mph and one of the greatest changes back then was to make the speedo to a higher mph. There were number of kits as a diode and capacitor was all you needed to change and the face was usually a decal.

The 4 cylinders were generally just over 100 mph and the GT could hit 115 to 119 usually in stock form. The headlight doors often come up at 110 mph.

This was the era where the automakers decided to put more numbers on to make customer feel better. Even today most say 130 mph even if they are limited to 110 mph.