Author Topic: rev counter  (Read 15240 times)

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mintex

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Re: rev counter
« Reply #60 on: April 17, 2016, 02:22:16 PM »

On a more serious technical note, to have any use other than being purely cosmetic, you want the tacho to match the rev range of your engine. I don't know what that is for the baby Fiats, but I imagine it's around 0-4000 rpm, with most of its life being spent around the 2000rpm mark.

For the Fiat you really want a 0-5000 (-ish) range, not something designed for an ultra-high revving motorcycle.

Yep, your spot on, Mine revs to 5000rpm with the most torque at about 2000rpm,not sure if that's the same for the air cooled or not  :)   
« Last Edit: April 17, 2016, 02:25:51 PM by mintex »
Dave

dombooth

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Re: rev counter
« Reply #61 on: April 17, 2016, 03:48:16 PM »
I seem to remember someone on here using one for a 2CV

mintex

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Re: rev counter
« Reply #62 on: April 17, 2016, 04:27:35 PM »
Dave

Joe Webb

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Re: rev counter
« Reply #63 on: April 17, 2016, 05:24:30 PM »
Yeah i realised that the rev range was way off, wasn't going to get it.

I have an idea of wiring in a variable resistor so i can calibrate a 4 cylinder with one of those tiny tachs but this is all theoretical at this point

That way i could potentially put the mechanism over a custom gauge face.
Thinking about maybe replacing the tyre pressure graphic in the dash with the tacho

Again, a lot of hard work and is just an idea :P
1999 Fiat 126p elx, 1971 Greeves Pathfinder, 72 Datsun 240z

Joe Webb

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Re: rev counter
« Reply #64 on: April 23, 2016, 12:06:25 AM »
Well I have a cheap tacho that looks pretty good actually and I have ordered some variable resistors to test my theory.

My next issue will be finding where to run the tach wire as my ELX has no distributor

if anyone knows where to run it that would be a great help

Cheers!

1999 Fiat 126p elx, 1971 Greeves Pathfinder, 72 Datsun 240z

mintex

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Re: rev counter
« Reply #65 on: April 23, 2016, 08:42:16 PM »
I can check on mine tomorrow but i'm sure i connected the rev counter to the - on the coil as mine has no dizzy either.

does yours have a coil like this one?



 
« Last Edit: April 23, 2016, 08:45:25 PM by mintex »
Dave

Joe Webb

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Re: rev counter
« Reply #66 on: April 23, 2016, 10:54:18 PM »
not sure, mine looks like the HT leads are coming from some kind of CDI

I guess it's the same thing though right?



1999 Fiat 126p elx, 1971 Greeves Pathfinder, 72 Datsun 240z

Joe Webb

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Re: rev counter
« Reply #67 on: April 25, 2016, 10:14:41 PM »
Well I got excited and hacked up my rev counter... before I have tested it.  :$

It should theoretically work, but I've probably made a mistake somewhere!

anyway what I've done so far was very simple. I cut some slots in the face surround so I could rotate it 90 degrees, but that was self explanatory. It allows me to mount it to the vertical face of the instrument cluster surround which is the only place I have space for it. It meant I had to dremel a new slot for the cylinder selection switch.

I figured out that the 8 cylinder setting has a resistance of around 400 kΩ and the 4 cylinder setting has around 200kΩ, so I bought a 100kΩ potentiometer and wired it in place of the 400kΩ resistor.

I chose a variable resistor to allow for any slight error in my extrapolation. Should be able to use it to calibrate the tach for my engine and get a more accurate reading.

Simple!

hopefully it will work





1999 Fiat 126p elx, 1971 Greeves Pathfinder, 72 Datsun 240z

Joe Webb

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Re: rev counter
« Reply #68 on: April 27, 2016, 03:53:39 PM »
yep... Knew I'd screw up somewhere.

got the resistances the wrong way round so I need an 800kΩ resistor for 2 cylinders.

That's quite cool though as it means you could calibrate it for basically any number of cylinders with the potentiometer as it will have a range of 0-1MΩ

with a twist of the dial you could take it from your 126 and put it in your V12 850 CSi, or your fiat coupé I5, or your 2 stroke saab ;)
1999 Fiat 126p elx, 1971 Greeves Pathfinder, 72 Datsun 240z

 

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