Technical Fitting a tachometer

[fiat500]

No-one actually needs to know the precise engine revs on a Fiat 500 but out of all the ancillary gauges you can fit, the one that would most grab my attention would be be something telling me the RPM of the engine.
I can see that some of them are crude devices which pickup from the ignition leads, some wire in to the LT circuit to the coil and there are also ones with a pickup and a magnet which I guess is to be fitted to the flywheel or a pulley.
Does anyone have one and what sort of revs are you getting at 60mph?

 

[Bigvtwin996]

No-one actually needs to know the precise engine revs on a Fiat 500 but out of all the ancillary gauges you can fit, the one that would most grab my attention would be be something telling me the RPM of the engine ..........

Never let it be said "I told you so...!" that 123 as the thin end of the wedge...
then the 650 upgrade, then the chequered rally look, then the Sporty Scoops...
now the extra gauges.... I reckon gull wing doors next.....big arches, big wheels, disk brakes....

 

[fiat500]

Never let it be said "I told you so...!" that 123 as the thin end of the wedge...
then the 650 upgrade, then the chequered rally look, then the Sporty Scoops...
now the extra gauges.... I reckon gull wing doors next.....big arches, big wheels, disk brakes....

[emoji3]... I didn't say I was going to do it... just asking for a friend. [emoji3]

 

[Bigvtwin996]

[emoji3]... I didn't say I was going to do it... just asking for a friend. [emoji3]

I can see it now...... in a year or so... just so Murp can cope with the rough roads...

 

[SDHXIII]

I can see it now...... in a year or so... just so Murp can cope with the rough roads...

Looks good on 13" rims!!!

 

[giardini]

I don't have a tacho either, but peak power is quoted at 4.400 rpm in the litterature I have, and I can't imagine there being loads of "over revs", so there's your ballpark I guess...

 

[Toshi 975]

I rigged up a tachometer on my standard 500L then gave it the full beans on a level road. It maxed out at about 5,700rpm and beyond any power band. I then had the cylinder head worked on, porting , valves and fitted the 126 28IMB carb on the enlarged inlet port. Went back to the same road to repeat the procedure and this time the engine maxed out at 6,500rpm at which point the standard cooling fan let go with some of the vanes piercing the cooling housing tinware

 

[giardini]

Just found an article that gives the gearing as 20.5 KMH per 1.000 RPM.

That sounds about right to me.

 

[fiat500]

Just found an article that gives the gearing as 20.5 KMH per 1.000 RPM.

That sounds about right to me.

I can't prove that this is correct but I worked it out a while ago:

https://www.fiatforum.com/500-classic/463651-top-speed-increase-126-bis-pinion.html?p=4364748

 

[giardini]

I can't prove that this is correct but I worked it out a while ago:

https://www.fiatforum.com/500-classic/463651-top-speed-increase-126-bis-pinion.html?p=4364748

OMG ! So you've sneakily been at this for a while. :doh:

That's like Galileo posting "Anyone here ever tried timing balls rolling down an incline ? Just asking for a friend who's obsessing a bit...".

 

[fiat500]

OMG ! So you've sneakily been at this for a while. :doh:

That's like Galileo posting "Anyone here ever tried timing balls rolling down an incline ? Just asking for a friend who's obsessing a bit...".

Never been compared with a Renaissance genius before; but I'll take that.

 

[giardini]

My emphasis was on the obsession, but they say genius is 10% inspiration and 90% perspiration, so you're still looking good

 

[fiat500]

My emphasis was on the obsession, but they say genius is 10% inspiration and 90% perspiration, so you're still looking good

:bang::bang::bang:

 

[Bigvtwin996]

OMG ! So you've sneakily been at this for a while. :doh:

That's like Galileo posting "Anyone here ever tried timing balls rolling down an incline ? Just asking for a friend who's obsessing a bit...".

Did you miss that Peter/Murph are the unofficial after market long term Fiat 500 Testing team...

 

[fiat500]

Did you miss that Peter/Murph are the unofficial after market long term Fiat 500 Testing team...

Yes, it's called Project LIFTOFF....Long, Interminable, Fanatical Trials Of a Fiat Fivehundred.[emoji3]

 

[lazylobster]

So, as you know, I now have a tach on mine. Cruising at 100kmh last night on the motorway, I’m at 3200 rpm. Which is surprising. Thought it would be higher?
Not complaining, as lower revs are good in not stressing the lump etc.

What is the maximum rpm of a 594cc engine?

R

 

[the hobbler]

That does seem to be very low revs for 62.5 mph---on a standard 500 I would have expected it to be more like 4,000/4,200rpm. My car has 13inch wheels and at 60mph the tacho shows 4,250rpm (14.13mph per 1,000rpm). might be worth getting both your speedo and tacho checked for accuracy---especially the speedo--a rolling road would be the best place)

 

[lazylobster]

Hi Tom, I have a sync gearbox fitted, maybe the final drive is lower ratio than the standard box?

I have a GPS based speedo on my phone, next time I'm out, I'll take some measurements. It won't be 100% accurate, but at least an indication.

Cheers
Rob

 

[fiat500]

Hi Tom, I have a sync gearbox fitted, maybe the final drive is lower ratio than the standard box?

One or both of your parameters will be wrong. The standard 126 final drive does have a better ratio than the 499 engine and gearbox but I'm not sure about the 594. In any case you would not be getting such a low RPM reading.

Your speedo will be reading wrong; mine was displaying an optimistic speed with a standard engine and box, an exact reading when I fitted the 126 setup and it is now reading about 10% slow with a 9:39 crownwheel and pinion.

I did soem calculations a while ago; they are probably wrong but I think that the principle is correct.

https://www.fiatforum.com/500-classic/463651-top-speed-increase-126-bis-pinion.html?p=4364748

 

[the hobbler]

Apologies Rob, forgot to answer your other question---a good condition 594 engine should be able to rev to 6,000rpm. If you take it much higher there is a chance that the fan will shed blades---NOT recommended!