85 MPH-to-120MPH speedometer swap

All Fiero Speedometers are interchangeable, although they do not look the same. The 85 MPH backlit speedo in the 85 and early 86 V6 cars can be replaced with a 120 mph speedo in less than 30 minutes.

"My '86 SE has the original wimpy 85 MPH speedo. I MAY have a source for a 120MPH speedo to replace it, but the 120 speedo is in a car with an automatic tranny, not 4-speed.

Has anyone on the list done this sort of transplant? Other than the speedo itself, what other parts either in the dash or down in the engine bay are required? Was there any calibration of the new speedo required to make it read within reason? Any nasty problems to watch out for when doing the swap?"

None - just put the speedo in. It is also easy to change or reset the odometer wheel while the speedo is out too, so you keep the same mileage. You can snap one out and the other in.

IRM has a NICE converson kit that will change a 85 mph speedo to a 140 mph speedo. THIS KIT ONLY WORKS WITH THE 85 MPH SPEEDO. Retail is about $100. It is backlit and matches the original very well.

From: Randy T. Agee

I'd just like to report that I recently installed the FOCOA 200 MPH speedo kit in my car. It is a replacement for the backlit 85 MPH factory one. All it is comprised of is a face sticker for the tach and the speedo and a crystal for the speedo calibration and a capacitor for the tach calibration.

The difference in the tach is that the redline is moved to 7500 RPMs and there is an "orange" line at 7000 RPMs. I didn't use the tach portion as I will NEVER rev my engine that high.

FOCOA was very helpful. Some ding dong at the post office was stealing the capacitor from the envelope. They sent me the cap. twice and it got stolen both times. (all I recieved was a direction sheet with a peice of tape where the cap used to be!!). So FOCOA finally put a third cap in a big, heavy box AND paid shipping to have it overnighted to me. I thought that was commendable of them.

The 200 MPH speedo is VERY nice and makes a world of difference to the driving ambience of the Fiero.

If any one wants to buy the tach portion of the kit, I'll let it go for $15.00. The whole kit costs $50.00.

From: Rick Stewart

"What is the formula for the speedometer? Can I change the crystal and recalibrate my speedometer to go higher?"

Okay, here's the speedometer formula:

Crystal frequency (approx.) in MHz = 534 / max_speed.

So, for the 120mph speedo it's 534/120 = 4.43 MHz
and for the 85mph speedo it's 534/85 = 6.33 MHz

Select the Xtal that matches your desired speedo range and recalculate:

534/freq = max

But the real problem is making the dial...

From: Oliver Scholz

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