Apologies if this is not the appropriate thread, chose it because the 127 also used the Fiat 100 Series engine along with the Autobianchi A112 and other models.

Anyway the Fiat 100 Series engine has fascinated me being a compact engine with a long production run, interested to know more about it particularly whether any experimental updates and unbuilt developments were considered for the engine over the years before it was eventually phased out in favour of the FIRE units in the mid-1980s?

Was the 1050cc version used in the A112 Abarth the absolute limit the engine capable of growing to in terms of displacement or was there still more scope for further enlargement (potentially overlapping with the Fiat 128 SOHC engine)?

I was always surprised they even expanded it to 1050. It was very old tech, and the far superior & hi-tech ohc “124 series” engines were available instead. I guess it was cheap to carry on making.

There would have been no point in making it any bigger, when the ohc engines already covered 994-1995cc in various models.

Have read the Fiat 128 engine was originally conceived as a 1-litre engine via Dante Giacosa's book though based on the figures of the 1.1 version, would guess it likely did not put out much more power compared to the 48 hp 965cc Fiat 100 Series engine.

Also heard of Abarth originally wanting to fit a 108 hp 982cc engine into the A112, along with murmurings of Abarth or someone else managing to further stretch the 100 Series engine to around 1150-1300cc+ (possibly in motorsport) to compete against the Mini and others.

While aware the 1049cc Fiat 124 Series was used in the Fiat 127 (and that a 1585cc with similar mods to Fiat 127 1.05 Sport could have theoretically been used on the 128 as a possible range-topper) , would it have been able to fit into a A112 (notwithstanding the later Y10)?

Additionally what is the exact relationship between the 100 Series engine to both the Topolino and 1100 engines? While it is known the engine was designed in about four months, have read claims the 100 Series unit was either inspired by the Topolino and 1100 engines or traces it linage back to the Topolino (and possibly 1100) engine?

There seems to be a lot of confusion here.

The Topolino engine was originally a side valve unit with aluminium cylinder head (500A). After the war it was fitted with a cast iron overhead valve head (5ooB) followed by the ali headed 500C. All had a vertical distributir drive at the camshaft drive end of the cylinder head. The 600 and 600D (a lot of changes from the 600) engines -which evolved into the 850/127/A112 engine - with the 850 engine running counter-clockwise - looked very similar with the obvious difference that the inlet manifold was cast into the head with a single horizontal port. The 128 engine was a totally different beast, intriducing a belt-driven OHC design to Fiats for the first time. The A112 Abarth had the Brazilian=built engine that was (as I recall) a different single OHC design.

The 1100 engine - type 103 - was another totallly separate design with pushrods and an ali head from the start.

The 124 was again totally different - starting out a pushrod operated unit and evolving into the classic twin cam with the residue of the original camshaft driving the distributor in its original position. Some variants of the twin cam had the distributr driven by skew gears off a camshaft and the Ritmo 130TC had it onthe end of a camshaft

Was under the impression that similar displacement aside the 70 hp 1050 A112 Abarth engine was unrelated to the Brazil built 1049cc version of the Fiat 124 Series engine, the former featuring OHVs while the latter featured an OHC (and was later turbocharged in the Y10 Turbo).

There is a brilliant English downloadable PDF about Dante Giacosa's book and all the fiats he was involved with. Google it

folgore said:

There is a brilliant English downloadable PDF about Dante Giacosa's book and all the fiats he was involved with. Google it

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I've got the book - brilliant, modest man. He had an aeronautical backround and was still thinking innovatively when he was older - envisaging springs in non-metallic materials and so on. The Topoloino was the first but not his only piece of brilliant design - the transverse leaf spring in the rear of the 128, for instance, was a masterpiece - light, compact, weight low down, doubled as an anti-roll bar - and he could foresee it in a composite material..

Have read the PDF, also have Luciano Greggio's Abarth book.

Found the following curious tidbit in Luciano Greggio's Abarth book regarding the Abarth-Simca 1300 GT on page 206, though whether the following displacement was ever truly applicable for a regular production spec 100 Series OHV engine is another matter.

The four-cylinder, 1288cc twin overhead cam engine - internal code 230 - had a bore and stroke of 76x71 mm and was the first power unit entirely designed by Abarth, inspired as it was in its basic architecture by the noted and well-tested Fiat-derived 982cc four-cylinder; Carlo Abarth adopted dry sump lubrication for the new unit with two geared pumps, one to distribute and one to recoup. With a compression ratio of 10.4:1 and fed by two twin-choke Weber carburettors, the engine generated a maximum 125 hp at 7200 rpm.

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