Highway RPM's

[TDecker]

Hi All,
I just got my '80 FI 2000 out on the freeway for the first time since I bought it and was surprised by how high the engine rev's at free way speed. I only took it up to 65ish. Should I be well above 3000RPM in 5th gear at those speeds?

(I found a discussion regarding differential replacement on older models that seems to indicate that the spider does indeed rev that high for modern freeway speeds.) I'd just like to verify that it holds true for "newer" models as it's a bit unnerving...
Tristan

[JohnMc]

They rev high!
After sorting everything out I took mine out on the freeway and got it up to 95 mph. Somewhere around 6,000 rpm's - great fun and ran it for about 15 miles passing many cars and getting thumbs up from some and fingers from others. (I do have "Z" rated tires that are pretty overkill to have on this car).
With this car I know that I won't have the car impounded for going 120 plus mph - something that just occasionally I used to do with other cars.
There is a replacement 5 speed that costs about $2k that has different 5th gear - see AR. Also some have changed out rear axle for lower gearing - but then it does effect the acceleration. Unfortunately no 6 speed that I have heard about - but would love one.

[ward00]

I had a link once for a 6 speed tranny, but it was with cross cut gears. The noise from the cross cut gears would make it unacceptable for street use, as I understand it.

[18Fiatsandcounting]

Should I be well above 3000RPM in 5th gear at those speeds?

Yes, this is normal. I seem to recall 70 mph is slightly below 4000 rpm (3800 or 3900 or so).

-Bryan

[redcars]

On my 82 70mph gives 3500 rpm and 80 mph gives 4000 rpm. This is normal for these cars and most all european cars of this age. I have run for hours at 4000 rpm. This is what these engines where built for. ENJOY

[MattVAS]

Those RPMs are normal but there are 2 ways to reduce them.

1. Find a good used Automatic Rear. These have a 3.58:1 ratio vs 3.9:1 that you have now.
2. Replace the transmission. The above poster mentioned replacement. But buy beware.... There are two different version of this replacement. The difference is that of the 5th gear. We'll call these type 1 and type 2 with factory listed as OE....
Type 1 - .82:1 5th gear
Type 2 - .78:1 5th gear (best ratio available)
OE - .87:1 5th gear

Other things to know about these replacement transmissions. They DO NOT FIT A FIAT 124 SPIDER! They must have a modification to them to fit. If you are buying one make sure the shifter will actually fit to your 124 hole. This is something we do here at VAS.

We no longer sell the Type 1 at VAS because the Type 2 is simply better.

[TDecker]

This is all helpful and comforting to know that it is indeed normal given my old Jensen Healey w/ a 4spd didn't rev that high while cruising...
Tristan

[Bjorn68]

Checked my 1974 CS1 with 1800 engine and 5 speed manual. I have 4000rpm already at 95km/h, which should be equal to 60mph, not 70mph.
I don't know the history of my car. The engine has been replaced with a European engine, so somewhere in that process, someone may have done someting to the transmission too. I don't really need all that acceleration, so any help on how to find out what could have been changed and how to restore it to original specs would be appreciated!
/Bjorn

[18Fiatsandcounting]

The first thing I would check is the accuracy of your speedometer and tachometer. They are not usually wrong by very much, but it can happen. The tachometer could be checked with a high quality external tachometer, and the speedometer can be verified using GPS or even the distance markers on the sides of some roads.

Given your 4000 rpm at 95 kph, it sounds like either the transmission or differential gearing was changed. Early stock spiders should be about 3400 rpm at that speed.

But, there is no way to look at the outside of the transmission and tell if it has been changed inside. You pretty much have to disassemble it, count the gear teeth, and do some calculations.

You might be able to get a crude estimate by removing the flywheel inspection plate, putting a mark on the flywheel with a pen or the like, rotating the engine by hand until the mark makes one full circle, and then counting exactly how far the output yoke of the transmission has rotated. This would require the car to be in gear, which means you'd have to raise one rear wheel off the ground so that it could spin. Laborious, but it could be done, and it might be accurate enough to see if you have the stock transmission ratios.

I believe a stock 1974 spider has a 0.881 ratio for 5th gear, which means if the flywheel rotates exactly one turn, the output shaft will turn 1.135 times (1 divided by 0.881). You could do the reverse method, that is, turn the output shaft exactly one full turn, and the flywheel should have turned 0.881 of a full revolution. Which is hard to measure of course. Perhaps count the flywheel teeth as you rotate it? I believe the flywheel ring gear has 134 teeth for every model except the early 1438 engines. So, if you turn the output shaft exactly one full turn, 118 teeth should have passed by a marker point. (134 times 0.881)

-Bryan

[Bjorn68]

Hi Bryan,
super useful help - thank you so much!
I'll start with checking the tachometer. There is probably an electronic circuit inside, which converts the pulses from the ignition coil to dc current and pass it through the coil which moves the needle. Anyone who has the schematic and knows how to open the tachometer?
/Björn

[18Fiatsandcounting]

That's exactly how they work. A pulse signal is converted to a DC voltage and the magnitude is dependent on the frequency of the pulse.

I do have a schematic that I believe is fairly generic for the Veglia tachometers, including the one used in the spiders. If you send me a private message with your email address, I can email it to you.

However, while not terribly complicated, the circuit does require you to know Zener diodes and an NPN from a PNP transistor, and how to test all this. I've taken tachometers apart and even replaced a faulty diode once, but I would have no idea how to properly calibrate them.

It would be far easier to take the car to an automotive shop that has a high quality diagnostic tachometer, and just have them test your engine at 4000 rpm in neutral to see if your tach is off.

-Bryan

[Nut124]

You can check the tach with an adjustable timing light w rpm indication.