Fiat 128 SOHC engine

Designed by Aurelio Lampredi, the Fiat SOHC engine first appeared in the front-wheel drive (FWD) Fiat 128 of 1969.[1] The in-line four-cylinder engine comprised an iron block with an aluminium 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 was driven by a 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) to an eventual 1900 cc (in the Fiat Linea). The Fiat 130 2.9 L (2,866 cc) V6 engine, 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. It was gradually replaced by the Pratola Serra engine series starting from 1995 (and in the 1100 cc guise, by the FIRE unit of comparable displacement), although it was also converted to use a multivalve DOHC head, giving birth to the Torque engine, used until 2005.

Fiat SOHC engine
Overview
ManufacturerFiat
Lancia
Zastava Automobiles
Tofaş
Production19692010
Layout
ConfigurationInline-4
Displacement1.1–1.8 L (1,116–1,839 cc)
Cylinder bore80–86.4 mm (3.15–3.40 in)
Piston stroke55.5–78.4 mm (2.19–3.09 in)
Block materialIron
Head materialAluminium
ValvetrainSOHC 2 valves x cyl.
Combustion
TurbochargerIn some versions
Fuel systemWeber carburetor
Multi-point fuel injection
Single-point injection
Fuel typeGasoline
Cooling systemWater-cooled
Output
Power output55–133 hp (41–99 kW)
Chronology
SuccessorPratola Serra modular engines
E.torQ engine
FIRE Turbojet/Multiair engine

Design and production

Cut apart 1,581 cc version of the 128 engine

The engine was designed as a transversely-mounted FWD-only power-plant being the second engine/gearbox combination to exhibit the now standard transverse engine-next-to-gearbox layout with unequal length driveshafts (the first was the Autobianchi Primula, the Mini had its gearbox in the sump of the engine). The exception to the engines 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 based longitudinally-mounted, front-engine, rear-wheel-drive layout platform. Unusual for the time was the electrically driven fan, rather than it being powered directly by the engine.[1] The 128 engine has five crankshaft 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 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.[1]

The 1.3 L (1,301 cc) version was turbocharged and used in the Fiat Uno Turbo. The 1.4 L (1,372 cc) 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 (appearing in 1,500 cc guise in the Lancia Delta/Prisma of the 1980s) as well as being used in the Fiat 128 derived Yugo.

The final incarnation of the 128 SOHC engine was modified to use 16 valves and double overhead camshafts. The engine (using the designation "Torque") initially featured the bore-spacing, bore and stroke of the 1.6 L (1,581 cc) 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 1372 block with a longer stroke, displacing 1.6 L (1,596 cc), ending production in 2005. The same stroke of the later version was also used in Brazil with the earlier Torque block, giving birth to an 1.8 L (1,839 cc) 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 80 mm × 55.5 mm (3.15 in × 2.19 in) to produce a displacement of 1.1 L (1,116 cc). The bore was increased to 86 mm (3.4 in) (maintaining the 55.5 mm (2.19 in) stroke) to give a displacement of 1.3 L (1,290 cc) for the X1/9. The original 1.3 L (1,290 cc) 128/X1/9 engine is the only one of the family to have used the 86 mm (3.4 in) bore. The second generation used bores of either 80 or 86.4 mm (3.15 or 3.40 in) with strokes of 55.5 or 63.9 mm (2.19 or 2.52 in) giving four possible engine capacities.[2] The final generation of SOHC engines standardised on a longer 67.4 mm (2.65 in) stroke with either an 80.5 or 86.4 mm (3.17 or 3.40 in) bore (giving 1.4 and 1.6 L (1,372 and 1,581 cc) respectively). The 67.4 mm (2.65 in) stroke with the 86.4 mm (3.40 in) bore was subsequently used by the early Torque engines, while the later Torque units used an 80.5 or 86.4 mm (3.17 or 3.40 in) bore with a 78.4 mm (3.09 in) stroke.

Valid engine bore/stroke combinations
Stroke
(mm)
Bore (mm)  
8080.58686.4
55.5 1116 1130 1290 1302 Capacity
(cc)
63.9 1285 1301 1485 1499
67.4 1355 1372 1566 1581
78.4 1576 1596 1821 1839
Key
1st generation  
1st & 2nd generation  
2nd generation  
3rd generation  
3rd generation & 1st generation Torque  
2nd generation Torque  

Engine specification (by engine-number)
Engine CodeBore (mm)Stroke (mm)Capacity (cc)
stated
Capacity (cc)
calculated
Production
(from - to)
BHPNotes
128.A.0008055.5111611161969–198255-65128
128.A1.0008655.5129012901971 - 7875-85128 Rally & Sport
128.AS.0008655.5129012901972–197875X1/9 1300
128.A.0648055.5111611161971–200855-64Zastava 101
128.A1.0648055.5111611161979–198364Zastava 101
128.A2.0648055.5111611161988–200860Zastava Koral/Yugo
128.AC.0008655.5129012901989–198373
128.A7.0648655.5129012901981–198665
128.A6.06486.455.5129813021987–200865
11.E1.0648055.5111611161986–199860
13.E1.06486.455.5129813021986–199865
13.E3.06486.455.5129813021988–199865Zastava Florida
11.MA.0648055.5111611161998–200860
13.MA.06486.455.5129813021998–200865
131.D1.01686.467.4158115811992-200296Tofaş Doğan and Kartal 1.6 S, SL, SLX (carb)
131.D2.01686.467.4158115811995-200292Tofaş Şahin S, Kartal
131.F3.01686.467.4158115811998-200296Tofaş Doğan and Kartal 1.6 S, SLX (i.e., cat)
131.F4.01680.567.4137213721995-200282Tofaş Şahin 1.4
138.A.0008055.5111611161978–198560Ritmo 60
138.A1.00086.455.5130113021978–198275-65Ritmo 65
138.A2.00086.463.9149814991978–198275-85X1/9 1500, Ritmo 75
138.A3.00086.455.513011302198275Ritmo S75
138.A4.00086.463.9149814991980–198275-85X1/9 1500, Ritmo S85
138.A5.00086.455.5130113021982–198570Also 138.AS.000
138.B.0008055.5111611161983–198555Uno 55
138.B1.0008055.5111611161982–198555-58Ritmo Mk II
138.B2.00086.455.5130113021983–198668-70Uno 70
138.B3.00086.463.9149814991982–198570-85Regata 85S
146.A4.0488055.5111611161985–198958,5Uno 60
146.A2.00080.563.9130113011985–1989105Uno Turbo Mk I
146.A2.14680.563.9130113011987–198999Uno Turbo Mk I (cat)
146.A2.24680.563.9130113011989–1991101Uno Turbo Mk II (cat)
146.A8.00080.567.4137213721989-1994118Uno Turbo Mk II
146.A8.04680.567.4137213721989-1993111Uno Turbo Mk II (cat)
146.C1.00080.567.4137213721989–199372Uno 70SXie
149.A7.00086.455.5130113021986–198965Uno 70SX
149.C1.00086.463.914981499198875Uno 75 SX i.e. (cat)/Selecta
159.A2.00080.567.4137213721990–199376Tipo/Tempra 1.4 (carb & i.e.)
159.A3.00086.467.4158115811990–199675-78Tipo/Tempra 1.6 (carb & i.e.)
159.B9.00086.467.415811584199690Tempra i.e.
160.A1.00080.567.4137213721988–199372Tipo/Tempra 1.4 i.e.
160.A1.04680.567.4137213721992–199369Uno Selecta
160.A2.00086.467.4158015811988–199383Tipo/Tempra 1.6 (carb & i.e.)
176.A4.00080.567.4137213721993–1995133Mk I Punto GT (GT1), CR 7.8:1
176.A4.00080.567.4137213721995–1997133Mk I Punto GT (GT2), CR 7.8:1
176.B6.00080.567.4137213721997–1999130Mk I Punto GT (GT3), CR 9.0:1
176.A9.00086.467.4158115811994–199788Mk I Punto Sporting & Cabrio
178.B3.00086.467.4158115811996–2005103DOHC 16v, Palio/Siena/Albea
182.A4.00086.467.4158115811995–2002103DOHC 16v, Bravo/Brava/Marea/Multipla/Lancia Dedra
182.B6.00080.578.4159615962002–2005103DOHC 16v, Marea/Multipla/Stilo/Palio/Siena/Strada/Doblò[3]
310 A3.01186.478.4183918392008–2010132DOHC 16v, Brazilian Linea 1.9 16v Torque
835.C1.00086.467.4158115811989–199575-78Tipo/Tempra 1.6 i.e. (Typ 160), Lancia Dedra Mk I (1.6 i.e.)
835.A1.04686.467.4158115811989–199475-78Lancia Dedra Mk I (1.6 i.e.)
835.A1.00086.467.4158115811995–199790Lancia Dedra Mk II (1.6 i.e.)

Applications

List of vehicles using variations of the Fiat SOHC engine.

Fiat

Lancia

Zastava

  • Yugo 55
  • Yugo 60
  • Yugo 65
  • Zastava 101
  • Zastava 128
  • Zastava Florida
  • Yugo Sana 1.3 1.4

Tofaş

Induction

Production

The Fiat SOHC used the full gamut of induction techniques through its long production run. The original 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 (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 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 1500/1600sohc 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 are used to feed a shared manifold do exist. DCNF's tend to be either 36 or 40 mm (1.4 or 1.6 in), the larger 44-DCNF is deemed too large for the engine. Both 40-DCOE and 45-DCOE are commonly used where space allows.[4]

For a normal street car DMTR carburator 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.[5] 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

Standard production camshaft specifications
ProfileDuration
(degrees)
Overlap
(degrees)
Lift
(mm)
Clearance (mm)
Inlet/Exhaust
Application
12/52-52/1224424--1.1 L 128 - European Specification
10/54-54/1024420--1.1 L 128 - North-American Specification
24/68-68/24272489.85-128 Rally
24/68-68/24272489.85-1300 X1/9 - European Specification
10/54-54/1024420--1300 X1/9 - North-American Specification
12/52-52/1224424--1300 X1/9 - Australian Specification
24/68-68/24272489.9-1500 X1/9 - European Specification (carb)
10/54-54/1024420--1500 X1/9 - North-American Specification (FI)
10/54-54/1024420--1500 X1/9 - Australian Specification (carb)
9/39-31/1228-212108-1.3 L Uno
0/30-40/10210-230108-1.3 L Uno Turbo
14/36-44/6230208.8-1.4 L Uno Turbo
7/35-37/5 222 12 8.8 0.4/0.5 1.6 Tipo
- 244 - 9.2 0.4/0.5 1.1/1.3 "DMB" Zastava - European Specification
- 256 - 9.2 - 1.6 90hp i.e. Punto/Tempra/Dedra

Aftermarket camshafts

Fast-road/race camshaft specifications
ManufacturerProfile nameProfileDuration
(degrees)
Overlap
(degrees)
Lift
(mm)
Clearance (mm)
Inlet/Exhaust
Application
KentFT735/67-67/352827010.330.20 / 0.20NA - fast road
KentFT852/76-76/5230810410.820.20 / 0.20NA - race
PiperBP27033/67-67/33280669.800.20 / 0.20NA - fast road
PiperBP28536/72-72/362887210.400.20 / 0.20NA - fast road
PiperBP30039/71-71/392907811.180.25 / 0.25NA - race
PiperBP32053/83-83/5331610611.180.25 / 0.25NA - race

Footnotes

  1. Becker, Clauspeter (1971), Logoz, Arthur (ed.), "Fiat 128", Auto-Universum 1971 (in German), Zürich, Switzerland: Verlag Internationale Automobil-Parade AG, XIV: 84
  2. Mazzocchi, Gianni, ed. (March 1979). "Fiat "Ritmo 75 CL" Automatica". Quattroruote (in Italian). Milan, Italy: Editoriale Domus. 24 (280): 84.
  3. Fiat Palio technical data (page 131, engine specification)
  4. To fit DCOE carburettors in an X1/9 a small amount of bodywork must be removed/reshaped
  5. 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.
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