Digiplex ignition Fiat Strada/Ritmo 130TC

Road-race engines and ancillaries - general discussion
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Robert
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Digiplex ignition Fiat Strada/Ritmo 130TC

Post by Robert »

Hello,

Is there someone who knows the map of Digiplex ignition system (Magnetti Marelli MED 408 A) of a Strada/Ritmo 130 TC ? Advance function of revs, load (manifold vacuum).

Thanks.
Guy Croft
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Post by Guy Croft »

To the best of my knowledge Robert, the map was never published in full anywhere public, even the OE workshop manual only had extracts from it.

GC
Robert
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Post by Robert »

Guy,

Thanks for this info. Could you provide this data on file format when you have time? This can help for ignition maping with other ECU.

Robert
Robert
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Post by Robert »

Guy and all other fans,

I found out this document concerning DIGIPLEX. It is the Lancia Trevi 2000 i.e one. I think it is different but quite similar. Sorry for the language of the document but curves & figures are international !!! Note that the "calculator" does not make interpolation between steps of pressure. I think it is only a hard-wired logic with a memory addressed by the "revs/position/pressure" digital image. The output (the memory values) is the advance.

Robert
PS: I will try to "reverse" the DIGIPLEX 408 (130TC) and I will post the map as soon I will succeed.
Attachments
Digiplex12.zip
(489.81 KiB) Downloaded 1338 times
NickRP
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Post by NickRP »

Hello Robert,

very interesting!

As for reversing it, the problem is that the code and the maps are stored in CPU internal ROM. The CPU has been custom labeled, and I didn't find any documents on its specs... I guess it is an MC6801 derivative...

Keep us updated,
Nikola Radenkovic
Robert
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Post by Robert »

Nick,

1/ In fact I planed to reverse the map by stimulating the digiplex (electrical is easy to me, vaccum less but I'm on going...) and see at the output the advance. I did it for the atmo pressure (without depression) and I found different resuls of the values inside the doc of the MED 408 (see below).

2/ looking for that I finally found some data from Magneti Marelli France (see attached file). Thanks to them !!!

3/ now I need the opinion of the MODERATOR (Guy?) because I don't understand the values of the advance at hi revs (44‚°) comparing to the values of the distributor system (34-36‚°). Furthermore GC advices 38‚° max if I remember well his book.

Hoping this sharing can help someone to map a more recent ECU. But from a competition point of view it is may be unuseful because the engine load and scavening leads to reduce advance compensating (?) the need of advance from the revs increase.... Guy ?

Robert
Attachments
MED 408.pdf
(496.96 KiB) Downloaded 1245 times
Guy Croft
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Post by Guy Croft »

hullo Rob, Nick

I am not getting much spare time at the moment - I already have an email from you Rob that I just have not had time to reply to. That said I have been watching this clever thread with great interest, well done both of you. I do wish more members would follow a thread through to some sort of conclusion; there only ever seem to be more questions..!

The short answer is that the part throttle advance does vary wildly throughout the load site range and over 36 deg deg advance at part throttle is not an uncommon ignition demand when tuning for max flexibility. And that behaviour is by no means confined to the 8v TC Fiat.

The full throttle ignition setting of the Digiplex at 6000rpm happens to be the same as the std distributor ie: 34-36 deg; quite right too, I myself have determined the same setting on mapped units. However at much higher engine speeds eg: 7000-8800rpm I have seen units need a lot more.

GC
Robert
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Post by Robert »

Guy,

Nice to "ear" you!
I'm not convinced that digiplex 408 (Ritmo 130TC) uses 36‚°. If you look at the file you can see that the max is 44‚°. To me it is quite huge...
Even if this map concerns production engine I can't understand the difference between distributor and digiplex, because for similar conditions (eg full load, full revs) they have to give the same "point".
Thank you to explain to us.

Robert
Guy Croft
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Post by Guy Croft »

Rob,

I have not had time to look at the 130TC download, but looking at my 105TC manual, the system on that motor (406A) only gives over 40 deg advance at manifold condition 0.28 bar vac and higher, ie: closing throttle.

36 deg max? Well, you have to play safe when calibrating a distributor, because it's not load sensistive.

GC
Robert
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Post by Robert »

I apologise. I understand that I did not catch that the higher is the vac lesser is the throttle !! Sorry for the confusion of my posts.

Have a good usage of the maps.

Robert
mtbr
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Post by mtbr »

Hello Guy, Rob and Nick,
1st post on this forum. I have a copy of the Fiat Manual for the 130TC.

The manual contains 8 graphs of "advance angle vs crankshaft speed", for manifold vacuum values of 20mm Hg to 300 mm Hg (approx 0.026 bar to 0.4 bar) in 40 mm Hg steps.

If any of you feel this information will be useful, I can scan these pages and post the graphs as PDF files.

M.
Robert
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Post by Robert »

Hello,

Hoping the file I've posted on dec 4th contains the same data. You can donwload it and verify. Thanks

Robert
mtbr
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Post by mtbr »

Robert wrote:Hello,

Hoping the file I've posted on dec 4th contains the same data. You can donwload it and verify. Thanks

Robert
The data is the same. The presentation is slightly different ad there are some tollerances for RPM and pressure.

M.
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