Fiat Dino Tacho

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Fiat Dino Tacho

Postby Stefan2000 » Mon May 18, 2015 8:23 am

I have a question concerning the tacho of my 1967 Dino Coupé.
It had a perfectly functioning dinoplex ignition and the tacho was working correctly, i exchanged the dinoplex for a 123 ignition and the only disadvantage of this is that my tacho is not reading correctly anymore, it's showing about twice the rpm. I expect the output signal from the red bosch coil is different than the Original Marelli coil. What's the best way to get it functioning properly with a red bosch coil?
I read some things at dinoplex.org about circuit board replacement but is it possible to get it functioning properly with the Original circuit board and how?

Thanks in advance!
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Re: Fiat Dino Tacho

Postby alh » Wed May 20, 2015 8:52 am

The electronic Veglia tach expects a square wave 12V signal, as coming from the distributor in a Dinoplex factory setup, it won't work with a high voltage pulse when connected to a coil minus terminal. What you could try as a work around is to put a 10K-47K resistor in-between the tacho wire and the coil minus terminal, and a 12V Zener diode between the tach wire (after the resistor) and ground.

simpletachoadapter.png
simpletachoadapter.png (13.95 KiB) Viewed 2254 times


Unfortunately, the 123 ignition/Bosch Red coil is not an ideal setup for the Dino engine, due to the low spark energy (similar to a points and coil setup) you get a relatively short and weak spark, whereas the Dino engine due to the fuel/air turbulence in the cylinders requires a strong spark to reach a good combustion rate. Fiat found this out the hard way with the first several hundred produced Dino cars, as a consequence Fiat then replaced the standard ignition setup against the F1 proven Dinoplex.

Good luck,
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Re: Fiat Dino Tacho

Postby Stefan2000 » Wed May 20, 2015 10:03 am

Thanks Adrian, i will definitly try. If i use a potentiometer instead of a 47k resistor, am i able to finetune the reading on the tacho?
What's the problem with the 123 ignition and red coil in your opinion? Is it the ignition itself or the coil output? And if it is the coil output can it be easily exchanged by a higher output coil and will this make any sense?
I would expect the red coil to be higher output than the Original point based marelli coil and that in combination with variable dwell contol from the ignition and EIX plugs would be a great improvement??? If i check my Sparks it looks pretty much like serious lightning to me, even stronger than the Original dinoplex (which might in real life does not mean much but anyway)
Please tell me for what reason you would prefer another system above this one, i'm really interested to know the technical reason because i'm not a serious in depth electo engineer or something.
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Re: Fiat Dino Tacho

Postby alh » Wed May 20, 2015 2:12 pm

You could try a 100K potentiometer for finding the best resistance as long as you don't go below 5K to avoid too much load on the Zener. I would just try a 10K, 33K, 47K or 68K resistor and keep the one which works best.

The problem with the 123 is the maximum specified "coil current", which is around 3.3-4 Ampere for the 123/Bosch coil setup. For the Dino engine you want to have 6-8 Amperes for an inductive ignition setup to produce a good and long spark. The IGBT transistor on the 123 controller board could handle a larger current but might have problems cooling the circuit sufficiently as the engine compartment heats everything up to around 80º C.
The Bosch Red coil manages a spark up to 15-20KV which is usually ok to ignite a spark in normal (not race derived) engines except with a richer fuel mix or on hot or cold starts (hence the ballast resistor which is shortened out while starting).

The factory Dinoplex/Marelli coil is a capacitive ignition developed for F1 racing engines and can create a maximum of 40-45KV secondary voltage, so no problem with the initial spark ignition here. The best alternative ignitions to the factory setup are either the high power Bosch ignition with an 8 Ampere coil, or an MSD 6A which is similar to the original DInoplex. Both rely on the original mechanical advance though. I designed a full electronic setup (no mechanical parts anymore) together with Rob from Carbonio for the Dino but this setup is still in testing and not yet available.
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Re: Fiat Dino Tacho

Postby alh » Wed May 20, 2015 2:14 pm

p.s. you can remove some of the problems with the weak output of the Bosch red coil by using NGK BPR7EIX spark plugs, they lower the secondary voltage required to create a spark due to the fine tip design.
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Re: Fiat Dino Tacho

Postby Tobi » Wed May 20, 2015 6:47 pm

Why did you replace your perfectly functioning dinoplex ignition?
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Re: Fiat Dino Tacho

Postby Stefan2000 » Thu May 21, 2015 8:28 am

I just wanted to fiddle with the ignition curve and that is fully adjustable on the 123 ignition. Beside that it has vacuum advance which i think is a must have on all cars, than it also has variable dwell and so on + it was cheap and i like milling, turning and welding.
And if it would not work as i wanted i could still put it back to Original spec in an hour or so. Maybe i will even do but to me it is/was interesting to be able to play with the parameters.

Adrian, that makes sense. The guy producing the 123 ignitions lives around the block for me so i'll might discuss with him what is possible and what not. If i understand you correctly the downside of this ignition is the maximum current output from the coil in combination with what the circuit board of the 123 could handle. So a higher output coil might raise your output but could damage the circuit board?
Temperature problem might be less of a problem in a fiat dino compared to a Ferrari dino because it right there with it's nose in the wind??? (well ofcourse it's behind the radiator) I can monitor the temperature from the 123 on my laptop and so far it never exceeded 60 degrees or something while driving.
Your right about the coil current, i can also monitor it on my laptop and it is somewhere inbetween 3 and 4 Amp's
I do drive the BPR7EIX Plugs.
Do i need a special zener diode, i see that for a 12V you can have 0W to 5W
http://www.dil.nl/Search.aspx?SearchFor=zener&QuickAbort=True
Thanks for the interesting reply!
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Re: Fiat Dino Tacho

Postby Tobi » Thu May 21, 2015 9:15 am

Stefan2000 wrote:I just wanted to fiddle with the ignition curve and that is fully adjustable on the 123 ignition. Beside that it has vacuum advance which i think is a must have on all cars, than it also has variable dwell and so on + it was cheap and i like milling, turning and welding.
And if it would not work as i wanted i could still put it back to Original spec in an hour or so. Maybe i will even do but to me it is/was interesting to be able to play with the parameters.


I completely understand this. Always nice to tweak and see what happens for a curious child - even if grown a bit ;)
I was afraid you'd have torn out a perfectly working Dinoplex - an ignition as iconic as the whole Dino engine - to replace it with some aftermarket thing that doens't even produce the performace of the original setup for some strange reason.
I'm not such a fanatic that puts originality above everything and tries to find NOS water for the coolant, but the ignition is sacrosanct to me. Changing the ignition is just next to changing the engine ;)
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Re: Fiat Dino Tacho

Postby Stefan2000 » Thu May 21, 2015 10:19 am

I agree, the original system is probably as iconic as the rest of the engine and from a point of view of preserving cultural heritage it would be dishonoures to just replace it with something new. But knowing i have this piece of cultural heritage stored in a box in my bedroom ready to bolt on, i don't really care.
You could discuss about the fact if it produces the performance of the orignal one or not. I did went to the Dyno with this exact setup and it produced about 15 more horsepower than the other couple of Dino 2000's he has had over the years on his dyno with a dinoplex system. From that perspective i would even think it's better if it can produce it's horsepower with a lot less output than with a lot of output from the ignition (which has to be generated by the alternator and that is driven by the engine and that costs horsepower)
https://www.youtube.com/watch?v=SC0bA_vHZZM


Think if Adrain comes up with a perfect replacement for the Original dinoplex with the benefits of the electronics (especially adjustable igniton curve and hopefully vacuum advance) and the charm of the dinoplex i will be the first in line :D
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Re: Fiat Dino Tacho

Postby Tobi » Thu May 21, 2015 10:41 am

Stefan2000 wrote:I agree, the original system is probably as iconic as the rest of the engine and from a point of view of preserving cultural heritage it would be dishonoures to just replace it with something new. But knowing i have this piece of cultural heritage stored in a box in my bedroom ready to bolt on, i don't really care.

This is the perfect basis for playin' around ;)

Stefan2000 wrote:You could discuss about the fact if it produces the performance of the orignal one or not. I did went to the Dyno with this exact setup and it produced about 15 more horsepower than the other couple of Dino 2000's he has had over the years on his dyno with a dinoplex system. From that perspective i would even think it's better if it can produce it's horsepower with a lot less output than with a lot of output from the ignition (which has to be generated by the alternator and that is driven by the engine and that costs horsepower)
https://www.youtube.com/watch?v=SC0bA_vHZZM

It would be very interesting to see the differences of your engine on the dyno with the original Dinoplex setup and the 123 setup. The 15 more hps compared to other engines may have many reasons. I don't think that the extra load of the alternator costs 15 hp.

Stefan2000 wrote:Think if Adrain comes up with a perfect replacement for the Original dinoplex with the benefits of the electronics (especially adjustable igniton curve and hopefully vacuum advance) and the charm of the dinoplex i will be the first in line :D

Maybe there is a way to trigger the Dinoplex with the signal of an 123 iginition instead of the original distributor. I don't think this is a serious setup, but this would allow you to adjust the map while having the spark from a Dinoplex. Again just for playin' around ...
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