Fiat 128 SOHC Engine
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Designed by
Aurelio Lampredi Aurelio Lampredi (16 June 1917 – 1 June 1989) was an Italian automobile and aircraft engine designer. Early career Lampredi was born in Livorno, Tuscany. He studied mechanical engineering at the Institut Technique Supérieur in Fribourg. A cl ...
, the Fiat SOHC engine first appeared in the
front-wheel drive Front-wheel drive (FWD) is a form of internal combustion engine, engine and transmission (mechanics), transmission layout used in motor vehicles, in which the engine drives the front wheels only. Most modern front-wheel-drive vehicles feature ...
(FWD)
Fiat 128 The Fiat 128 is a transverse front-engine, front wheel drive small family car manufactured and marketed by Fiat from 1969 to 1985 as a two- or four-door sedan, three- or five-door station wagon as well as two- or three-door coupé. The 128 runn ...
of 1969. The in-line four-cylinder engine comprised an iron
block Block or blocked may refer to: Arts, entertainment and media Broadcasting * Block programming, the result of a programming strategy in broadcasting * W242BX, a radio station licensed to Greenville, South Carolina, United States known as ''96.3 ...
with an
aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
cylinder-head containing a single overhead camshaft operating directly on both the inlet and exhaust valves in a reverse-flow cylinder-head configuration. The
camshaft A camshaft is a shaft that contains a row of pointed cams in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines (to operate the intake and exhaust valves), mechanically controlled ignition syst ...
was driven by a toothed belt rather than chain. The engine remained in production until about 2010 and grew in capacity over the years from 1100 cc (in the
Fiat 128 The Fiat 128 is a transverse front-engine, front wheel drive small family car manufactured and marketed by Fiat from 1969 to 1985 as a two- or four-door sedan, three- or five-door station wagon as well as two- or three-door coupé. The 128 runn ...
) to an eventual 1900 cc (in the Fiat
Linea ''Linea'' () is a genus of foraminifera belonging to the subfamily Rhabdammininae. It is a monotypic genus containing the sole species ''Linea simplex'' (). It was described in 1989 from samples of foraminifera collected at the Nares Abyssal Pl ...
). The Fiat 130
V6 engine A V6 engine is a six- cylinder piston engine where the cylinders and cylinder blocks share a common crankshaft and are arranged in a V configuration. The first V6 engines were designed and produced independently by Marmon Motor Car Company, ...
, also appearing in 1969, although having crossflow cylinder head, is directly related to the 128 SOHC engine, but with a 1.20 upscale in bore and stroke. The 128 SOHC engine was gradually replaced by the Pratola Serra engine series starting from 1995, and in the 1100 cc guise, by the
FIRE Fire is the rapid oxidation of a fuel in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. Flames, the most visible portion of the fire, are produced in the combustion re ...
unit of comparable displacement. It was also converted to use a multivalve
DOHC An overhead camshaft (OHC) engine is a piston engine in which the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combus ...
head, giving birth to the Torque engine, used until 2005.


Design and production

The engine was designed as a transversely-mounted FWD-only power-plant, being the second engine/
gearbox A transmission (also called a gearbox) is a mechanical device invented by Louis Renault (who founded Renault) which uses a gear set—two or more gears working together—to change the speed, direction of rotation, or torque multiplication/r ...
combination to exhibit the now standard transverse ''engine-next-to-gearbox'' layout with unequal length
driveshaft A drive shaft, driveshaft, driving shaft, tailshaft (Australian English), propeller shaft (prop shaft), or Cardan shaft (after Girolamo Cardano) is a component for transmitting mechanical power, torque, and rotation, usually used to connect ...
s (the first was the
Autobianchi Primula The Autobianchi Primula is a Supermini car, supermini economy car manufactured between 1964 and 1970 by the Italy, Italian automaker Autobianchi, partly owned by and later a subsidiary of the Fiat, Fiat Group. The Primula was Fiat's first model wi ...
drive-train, the
Mini The Mini is a very small two-door, four-seat car, produced for four decades over a single generation, with many names and variants, by the British Motor Corporation (BMC) and its successors British Leyland and the Rover Group, and finally ...
had its gearbox in the sump of the engine). The exception to the engine's FWD-only design is its revolutionary use as a mid-engine drive-train in the Fiat X1/9. Also, Tofaş has adapted 128 engines into its
Fiat 131 The Fiat 131 is a mid-size family car manufactured and marketed by Fiat from 1974 to 1984 after its debut at the Turin Motor Show#1974, 1974 Turin Motor Show. Available as a two-door and four-door Saloon (car), saloon and 5-door station wagon, ...
based longitudinally-mounted,
front-engine, rear-wheel-drive layout A front-engine, rear-wheel-drive layout (FR), also called Système Panhard is a powertrain layout with an engine in front and rear-wheel-drive, connected via a drive shaft. This arrangement, with the engine straddling the front axle, was the t ...
platform. Unusual for the time was the electrically driven fan, rather than it being powered directly by the engine. The 128 engine has five
crankshaft A crankshaft is a mechanical component used in a reciprocating engine, piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating Shaft (mechanical engineering), shaft containing one or more crankpins, ...
bearings. A prominent feature of the Fiat SOHC engine is its massively over-square proportions. This over-square design allows large (within the constrains of a reverse-flow configuration) valve sizes relative to engine capacity. A secondary benefit is the short crank throw, which reduces the accelerative forces on the con-rod allowing the engine to operate at significantly increased engine-speeds. The original engine's limit was only reached at 8000 rpm. The version was
turbocharged In an internal combustion engine, a turbocharger (also known as a turbo or a turbosupercharger) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake air, forcing more air into the ...
and used in the
Fiat Uno The Fiat Uno is a supermini manufactured and marketed by Fiat. Launched in 1983, the Uno was produced over a single generation (with an intermediate facelift, 1989) in three and five-door hatchback body styles until 1995 in Europe — and un ...
Turbo. The unit was also turbocharged and first used in the MkII Uno Turbo, then in the Punto GT. As with its bigger brother the famous Fiat DOHC ( aka Fiat/Lancia Twincam) engine, the Fiat SOHC engine was shared with the Fiat subsidiary
Lancia Lancia Automobiles S.p.A. () is an Italian car manufacturer and a subsidiary of Stellantis Europe, which is the European subsidiary of Stellantis. The present legal entity of Lancia was formed in January 2007 when its corporate parent reorganise ...
(appearing in 1,500 cc guise in the
Lancia Delta The Lancia Delta (stylized Lancia Delta (letter), δ) is a small family car produced by Italian automobile manufacturer Lancia in three generations. The first generation (1979–1994) debuted at the 1979 Frankfurt Motor Show#1979, Frankfurt Motor ...
/ Prisma of the 1980s) as well as being used in the Fiat 127 derived Yugo. The final incarnation of the 128 SOHC engine was modified to use 16 valves and
double overhead camshaft An overhead camshaft (OHC) engine is a piston engine in which the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combus ...
s. The engine (using the designation "Torque") initially featured the bore-spacing, bore and stroke of the 159/160 series engine with a new 16 valve DOHC crossflow cylinder-head. To incorporate the extra oil-return-paths and symmetrical head (as opposed to the asymmetrical SOHC head) the cylinder-block was slightly revised making the DOHC head non-interchangeable with the previous incarnations of the 128 engine. It powered the Brava/Bravo, Marea and Multipla Fiat automobiles as well as the second-generation Lancia Delta. It was then replaced with a version based on the 1.4 L (1,372 cc) block with a longer 78.4 mm stroke, displacing , ending production in 2005. That same stroke of the later version was also used in Brazil with the earlier 1.6 L block, giving birth to a version, used in the Linea.


Engine specification

The Fiat SOHC engine was produced in a number of configurations differing in stroke and bore, but maintaining a standard bore-spacing. The first generation of 128 derived engines used a bore and a stroke of to produce a displacement of . The bore was increased to (maintaining the stroke) to give a displacement of for the 128 Rally. This engine was later used in the 128 Coupé and X1/9. The original 128/X1/9 engine is the only one of the family to have used the bore. The second generation used bores of either with strokes of giving four possible engine capacities. The final generation of SOHC engines standardised on a longer stroke with either an bore (giving respectively). The stroke with the bore was subsequently used by the early Torque engines, while the later Torque units used an bore with a stroke.


Applications

List of vehicles using variations of the Fiat SOHC engine.


Fiat

*
Fiat 128 The Fiat 128 is a transverse front-engine, front wheel drive small family car manufactured and marketed by Fiat from 1969 to 1985 as a two- or four-door sedan, three- or five-door station wagon as well as two- or three-door coupé. The 128 runn ...
: 1969-1985 * Fiat X1/9: 1972-1989 * Fiat Ritmo/Strada: 1978-1988 * Fiat 131 Mirafiori: 1980-1984 *
Fiat 147 The Fiat 147 was a three-door hatchback subcompact car produced by Fiat in the Brazilian state of Minas Gerais from autumn 1976 until 1987, when it was replaced by the Fiat Uno. It was the Brazilian variant of the Fiat 127. Some were also buil ...
: 1982 (Argentina) *
Fiat Uno The Fiat Uno is a supermini manufactured and marketed by Fiat. Launched in 1983, the Uno was produced over a single generation (with an intermediate facelift, 1989) in three and five-door hatchback body styles until 1995 in Europe — and un ...
: 1983-1989 * Fiat Regata: 1985-1990 * Fiat Spazio/Vivace: 1991-1996 * Fiat Tipo: 1988-1995 * Fiat Tempra: 1990-1995 * Punto Mk I: 1993-1999 * Fiat Palio/Siena: 1996-2002


Lancia

*Lancia
Delta Delta commonly refers to: * Delta (letter) (Δ or δ), the fourth letter of the Greek alphabet * D (NATO phonetic alphabet: "Delta"), the fourth letter in the Latin alphabet * River delta, at a river mouth * Delta Air Lines, a major US carrier ...
: 1979-1994 *Lancia Prisma: 1980s *Lancia Dedra: 1990-1998


Zastava

*Yugo 55 *Yugo 60 *Yugo 65 *Zastava 101 *Zastava 128 *Zastava Poly *Zastava
Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...
*Yugo Sana 1.3 1.4


Tofaş

* Tofaş Şahin/Doğan/Kartal: 1992-2002


Induction


Production

The Fiat SOHC used the full gamut of induction techniques through its long production run. The 128 and 138 series engines originally used a single down-draught carburettor. The carburettor was normally of progressive twin-choke design (two asymmetric sized chokes operated progressively) such as the Weber DMTR and DATR of the X1/9.
Multi-point fuel injection Fuel injection is the introduction of fuel in an internal combustion engine, most commonly automotive engines, by the means of a fuel injector. This article focuses on fuel injection in reciprocating piston and Wankel rotary engines. All co ...
(MPI) was introduced late in the 138 series to help meet lowered emission requirements in the US. The original MPI system comprised a large cylindrical plenum running parallel to the engine with individual runners to each inlet port and a single throttle controlling air-flow into the plenum. This plenum was pressurised in the Mk I Uno Turbo. The plenum was slightly redesigned to a more angular "box" shape for the 3rd generation engines and was again pressurised for the Uno and Punto GT Turbo models. For the 3rd generation engines, the down-draft carburettor was replaced with a Single-point injection system (SPI) in the base-level models. The SPI system mounts on a manifold similar to that of the carburetted models and looks, as well as acts, much like a single-choke carburettor with a single throttle plate but no venturi and a centrally mounted single injector.


Tuning & modification

Since the Fiat SOHC engine series was produced for a long time and has been used in a lot of cars, it was just matter of time before people realized you can tune them fairly easily. They are oversquared by design, SOHC heads flow very well and 1500/1600 SOHC engines come with forged rods. The Fiat Tipo/Tempra/Punto 1.6 8v (75-90hp) is commonly used as a base because it's easily accessible and is de-tuned from factory (especially the 75hp versions), leaving tuners with a lot of headroom for horsepower increase. Common modifications are: swapping to a better carburetor, using a higher overlap/lift camshaft, bigger intake/exhaust valves, lowering the head to increase compression and a tuned 4-2-1 exhaust manifold. Most of these modifications are very cheap to do since you can use the parts from Fiat/Zastava parts bin.


Carburettor

Traditionally both down-draft (DCNF & IDF) and side-draft ( DCOE) twin-choke carburettors have been used to extract more power from the 128 derived engines. IDFs are rarely used due to an incorrect orientation of the float-bowls (causing possible surge/starve issues under cornering), the correctly orientated DCNF being the preferred down-draft carburettor in this application (also having a much lower profile than the IDF). For ultimate power the DCOE carburettor is used even though the float-bowl direction matches that of the IDF (i.e. incorrect). The aforementioned carburettors are usually used in pairs (effectively giving one independently tuneable carburettor per engine-cylinder), though applications where a single DCNF/DCOE is used to feed a shared manifold do exist. DCNF's tend to be either , the larger 44-DCNF is deemed too large for the engine. Both 40-DCOE and 45-DCOE are commonly used where space allows. For a normal street car, a DMTR carburetor is commonly used in sizes varying from 32/32, 32/34 to 34/34.


MPI

Tuning of the early MPI systems has previously been difficult as the electronic control systems are analogue, making them difficult to "re-map". Low-cost DIY Fuel Injection (FI) controllers (such as MegaSquirt) have made it easier to alter the characteristics of the early MPI systems and release similar potential as the DCNF/DCOE carburettors. It is possible to "chip" the later digital MPI systems, though aftermarket FI controllers again give greater flexibility.


Throttle bodies

Individual FI Throttle Bodies (TBs) are available for mounting to DCNF and DCOE manifolds as well as custom-built FI systems which, with aftermarket controllers, give the most flexibility and control over fuelling out of all the options.


Motorcycle carburettors

Motorcycle, or "bike" carburettors, being a modern and cost-effective alternative to DCOE/DCNFs, have been adapted to work with the 128-derived engines. They potentially offer better control over fuelling than DCNF/DCOE, but their use on the Fiat SOHC engine is still in its infancy.


Camshaft profile

The camshaft was a main methods of varying the 128 series engines characteristics for different applications/markets. The high-revving oversquare design of the 128 engine lends itself to high-overlap high-duration cam profiles better than more traditional square/under-square engine designs without losing drivability.The standard European carburettord X1/9 used a camshaft more radical than many after-market "performance" camshafts offered for contemporary engines from other (non Italian) European manufacturers. Though a beneficial characteristic for sports orientated engine the high-overlap high-duration cam design gives poor emissions output which was unacceptable under the tightened US emissions regulations. To remedy this (in addition to the introduction of MPI) camshafts for emission-restricted markets featured asthmatic low-lift, low-duration, low-overlap profiles totally unsuited to the nature of the 128 engine.


Factory produced camshafts


Aftermarket camshafts


Footnotes

{{Reflist
SOHC An overhead camshaft (OHC) engine is a piston engine in which the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combus ...
Straight-four engines Gasoline engines by model