Wanted: Ignition advance curves Marelli S144 / S144B Distributors

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Spider 1969
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Wanted: Ignition advance curves Marelli S144 / S144B Distributors

Post by Spider 1969 » Wed Jul 27, 2016 8:31 pm

Hi All,

As I may have issues with an aftermarket electronic ignition I'm using I would like to go back (temporary) to a CB distributor with mechanical advance.

I have two Magneti Marelli ones available: S144 and S144B. Both originate from Fiat TC 1608cc 125 type engines. (as far as I'm aware because I took them of them).
Before fitting either one of them I would like to know the advance curve.

Only data I have available available comes from the "caratteristiche e dati" (technical specs) for the Fiat 124 Sport 1600 spider / coupe from 1970.

This however specifies the distributor for this type of engine as S134B thus not the two ones I have in my possession.
Maximum mechanical advance is specified ad 26 degrees for this distributor but is not specified at which rpm (see attached photo)

Searching the web did not lead to any results on advance data for the S144 and S144B.

Does any one of the members have the following data for the S144 and S144B?
- RPM at which mechanical advance starts.
- Maximum mechanical advance and RPM at which this is achieved.

Looking forward to replies.

Best reghards,

Charles
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Guy Croft
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Re: Wanted: Ignition advance curves Marelli S144 / S144B Distributors

Post by Guy Croft » Thu Jul 28, 2016 5:49 pm

the S144 curve from the 124 CSA MUST have been derived by dyno-test because it has 5 deg static not 10 and peaks at 3500 not 5500.

Niels van Buuren and Miles Thacker set to work on this question on my works a few weeks ago, I asked them to work out "why was it different from all the other TC atmo curves?"

their ultimate reasoning was flawless - it gave more power on dyno test but not used in general production to reduce the risk of detonation.

I let them figure it out on their own and their conclusions - in my view - were 100% correct.

G
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Guy Croft, owner

Spider 1969
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Re: Wanted: Ignition advance curves Marelli S144 / S144B Distributors

Post by Spider 1969 » Thu Jul 28, 2016 10:21 pm

Thanks Guy,

Is the CSA distributor numbered S144 or does it have additional letters or numbers?

Interestingly my 123 distributor offers several curves which also peak at 3500 rpm.
Sofar I've used the curve that should resemble the a 134B (1608) distributor and it is specified by 123 to peak at 3500 with 36 degrees of advance. Not sure whether this is really to Fiat specification because as said peak rpm is not specified in their manual for this distributor.
I presumed that this figure includes 10 degrees of static advance because 26 degrees has been specified by Fiat. When asked 123 they replied that it is without static timing. This would mean that up until now I have run at 46 degrees of advance above 3500 rpm because I've set it static at 10 degrees.
I have not experienced detonation and I have been to the dyno with this setting. Either advancing or retarding did not produce more power on the dyno test. However I do not feel comfortable so will do some testing to see if it really produces 46 total advance. There may be other issues as I've noticed timing on engine idling is around 15 to 20 degrees where as I've set its static at 10 degrees. Hence the temporary return to the CB distributor.

Sincerely,

Charles
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Guy Croft
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Re: Wanted: Ignition advance curves Marelli S144 / S144B Distributors

Post by Guy Croft » Fri Jul 29, 2016 12:32 pm

it's S144BA on the 124 CSA 8v 1800..

Ignoring vacuum advance the most important thing with the 8v TC is to have no more than 36 deg total advance - but it could be a bit less - and that peak advance (static plus centrifugal) can be at 3500 like the Abarth version - or at 5500 like the other models.

The CSA for example (see graph above) was set at 5 static plus 24-28 centrifugal, giving a max total advance at 3500 of 29-33 deg.

Vacuum advance only feeds in more advance than the centrifugal curve when there is an inlet manifold vacuum condition, ie: at part throttle.
Guy Croft, owner

Spider 1969
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Joined: Sun Sep 22, 2013 7:21 pm
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Re: Wanted: Ignition advance curves Marelli S144 / S144B Distributors

Post by Spider 1969 » Fri Jul 29, 2016 9:52 pm

I would guess that both my distributors give 26 degrees at 5500. I will test this coming days and feedback.
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