Fiat SOHC
Encyclopedia
Designed by Aurelio Lampredi
, the Fiat SOHC engine first appeared in the front-wheel drive
(FWD) Fiat 128
of 1969. The in-line four-cylinder engine comprised an iron block
with an aluminium
cylinder-head
containing a single over-head 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 the mid 1990s and grew in capacity over the years from 1100 cc (in the Fiat 128
) to an eventual 1600 cc (in the Fiat Tipo
/Tempra
). Also appearing in 1969, the Fiat V6 130 engine 2866 cc, although no reverse-flow cylinder-head, is directly related to the 128 SOHC engine, with a 1.20 upscale in bore and stroke.
mounted FWD-only power-plant being the first engine/gearbox combination to exhibit the now standard transverse engine-next-to-gearbox layout with unequal length driveshaft
s (the Mini
had its gearbox in the sump of the engine). The one exception to the engines FWD-only design is its revolutionary use as a mid-engine drive-train in the Fiat X1/9
.
A prominent feature of the Fiat SOHC engine 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 Engine was developed for forced-induction use in the Fiat Uno
Turbo Mk I and further refined for the MK II and later 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 1500 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 utilise 16 valves and dual cam shafts. The engine (using the designation "Torque") featured the bore-spacing, bore and stroke of the 1580 cc 159/160 series engine with a new 16v DOHC cylinder-head. To incorporate the extra oil-return-paths and symmetrical head (as opposed to the asymmetric SOHC head) the cylinder-block was slightly revised making the DOHC head non-interchangeable with the previous incarnations of the 128 engine. Development of the Torque engine took place in the US rather than Italy whilst Fiat was in partnership with GM. The Torque engine (178.B3 - 182.A4) powered the Brava/Bravo, Marea and Multipla Fiat automobiles as well as the second-generation Lancia Delta (never sold in the UK) finally ending production in 1999.
) 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.
Aurelio Lampredi
Aurelio Lampredi was an Italian automobile and aircraft engine designer.Born in Livorno, he began his career at Piaggio, makers of the Vespa scooter, but quickly moved up to larger engines...
, the Fiat SOHC engine first appeared in the front-wheel drive
Front-wheel drive
Front-wheel drive is a form of engine/transmission layout used in motor vehicles, where the engine drives the front wheels only. Most modern front-wheel drive vehicles feature a transverse engine, rather than the conventional longitudinal engine arrangement generally found in rear-wheel drive and...
(FWD) Fiat 128
Fiat 128
The Fiat 128 is a small family car manufactured by the Italian manufacturer Fiat from 1969 to 1985. The engine was designed by the famous Ferrari racing engine designer Aurelio Lampredi.-History:...
of 1969. The in-line four-cylinder engine comprised an iron block
Cylinder block
A cylinder block is an integrated structure comprising the cylinder of a reciprocating engine and often some or all of their associated surrounding structures...
with an aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
cylinder-head
Cylinder head
In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket...
containing a single over-head camshaft operating directly on both the inlet and exhaust valves in a reverse-flow cylinder-head
Reverse-flow cylinder head
A reverse-flow or non-crossflow cylinder head is one that locates the intake and exhaust ports on the same side of the engine. The gases can be thought to enter the cylinder head and then change direction in order to exit the head...
configuration. The camshaft
Camshaft
A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...
was driven by a belt rather than chain. The engine remained in production until the mid 1990s and grew in capacity over the years from 1100 cc (in the Fiat 128
Fiat 128
The Fiat 128 is a small family car manufactured by the Italian manufacturer Fiat from 1969 to 1985. The engine was designed by the famous Ferrari racing engine designer Aurelio Lampredi.-History:...
) to an eventual 1600 cc (in the Fiat Tipo
Fiat Tipo
The Fiat Tipo is a small family car designed by the IDEA design house and produced by the Italian manufacturer Fiat between 1988 and 1995.The Tipo was initially available only as a five-door hatchback. The car was made entirely out of galvanized body panels to avoid rust, and was built on a...
/Tempra
Fiat Tempra
The Fiat Tempra is a small family car produced by Italian automaker Fiat from 1990 to 1998. The Tempra was intended as a replacement for the Fiat Regata. The original project was called Tipo 3, being a mid-size car between the Fiat Tipo and the bigger Fiat Croma...
). Also appearing in 1969, the Fiat V6 130 engine 2866 cc, although no reverse-flow cylinder-head, is directly related to the 128 SOHC engine, with a 1.20 upscale in bore and stroke.
Design and production
The engine was designed as a transverseTransverse engine
A transverse engine is an engine mounted in a vehicle so that the engine's crankshaft axis is perpendicular to the long axis of the vehicle. Many modern front wheel drive vehicles use this engine mounting configuration...
mounted FWD-only power-plant being the first engine/gearbox combination to exhibit the now standard transverse engine-next-to-gearbox layout with unequal length driveshaft
Driveshaft
A drive shaft, driveshaft, driving shaft, propeller shaft, or Cardan shaft is a mechanical component for transmitting torque and rotation, usually used to connect other components of a drive train that cannot be connected directly because of distance or the need to allow for relative movement...
s (the Mini
Mini
The Mini is a small car that was made by the British Motor Corporation and its successors from 1959 until 2000. The original is considered a British icon of the 1960s, and its space-saving front-wheel-drive layout influenced a generation of car-makers...
had its gearbox in the sump of the engine). The one exception to the engines FWD-only design is its revolutionary use as a mid-engine drive-train in the Fiat X1/9
Fiat X1/9
The Fiat X1/9 is a two-seater mid-engined sports car designed by Bertone and manufactured by Fiat from 1972-1982 and subsequently by Bertone from 1982-1989....
.
A prominent feature of the Fiat SOHC engine 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 Engine was developed for forced-induction use in the Fiat Uno
Fiat Uno
The Fiat Uno is a supermini car produced by the Italian manufacturer Fiat. The Uno was launched in 1983 and built in its homeland until 1995, with production still taking place in other countries.-First series :...
Turbo Mk I and further refined for the MK II and later the Punto GT.
As with its bigger brother the famous Fiat DOHC
Fiat Twin Cam engine
Designed by Aurelio Lampredi the Fiat Twin Cam was an advanced inline-4 automobile engine produced from 1959 through 1994 as a Fiat/Lancia engine until it was replaced by the "family B" series of engines...
(aka Fiat/Lancia twincam) engine, the Fiat SOHC engine was shared with the Fiat subsidiary Lancia
Lancia
Lancia Automobiles S.p.A. is an Italian automobile manufacturer founded in 1906 by Vincenzo Lancia and which became part of the Fiat Group in 1969. The company has a long history of producing distinctive cars and also has a strong rally heritage. Some modern Lancias are seen as presenting a more...
(appearing in 1500 cc guise in the Lancia Delta
Lancia Delta
The Lancia Delta is a small family car produced by Italian automaker Lancia with the first generation being produced between 1979 and 1994, the second generation running from 1993 until 1999, and the third generation Delta entering production in 2008. It was first shown inFrankfurt Motor Show in 1979...
/Prisma
Lancia Prisma
The Lancia Prisma was a midsize car built by Lancia in the 1980s. It was basically a sedan version of the Lancia Delta, and like its smaller hatchback "brother", shared its chassis and engines with the Fiat Ritmo and Regata...
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 utilise 16 valves and dual cam shafts. The engine (using the designation "Torque") featured the bore-spacing, bore and stroke of the 1580 cc 159/160 series engine with a new 16v DOHC cylinder-head. To incorporate the extra oil-return-paths and symmetrical head (as opposed to the asymmetric SOHC head) the cylinder-block was slightly revised making the DOHC head non-interchangeable with the previous incarnations of the 128 engine. Development of the Torque engine took place in the US rather than Italy whilst Fiat was in partnership with GM. The Torque engine (178.B3 - 182.A4) powered the Brava/Bravo, Marea and Multipla Fiat automobiles as well as the second-generation Lancia Delta (never sold in the UK) finally ending production in 1999.
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 stroke of 55.5 mm and a bore of 80 mm to produce a displacement of 1116 cc. The bore was increased to 86 mm (maintaining the 55.5 mm stroke) to give a displacement of 1290 cc for the X1/9. The original 1290 cc 128/X1/9 engine is the only one of the family to have used the 86 mm bore. The second generation used bores of either 80 mm or 86.4 mm with strokes of 55.5 mm or 63.9 mm giving four possible engine capacities. The final generation of SOHC engines standardised on a longer 67.4 mm stroke with either an 80.5 mm or 86.4 mm bore (giving 1372 cc and 1581 cc respectively).EWLINE
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Fiat
- Fiat 128Fiat 128The Fiat 128 is a small family car manufactured by the Italian manufacturer Fiat from 1969 to 1985. The engine was designed by the famous Ferrari racing engine designer Aurelio Lampredi.-History:...
: 1969-1985 - Fiat RegataFiat RegataThe Fiat Regata is the saloon version of the Fiat Ritmo small family car, produced by Italian automaker Fiat. It was produced from 1983 to 1990, corresponding to the post-facelift Ritmo. The Regata had a choice of three gasoline and two diesel engines...
: 1985-1990 - Fiat Ritmo/StradaFiat RitmoThe Fiat Ritmo is an automobile from the Italian manufacturer Fiat, launched in 1978. Styled by Bertone of Italy, it was seen by some as the most distinctive looking small family car in Europe on its launch in 1978 Turin Motorshow. It was badged in Great Britain and North America as the Fiat Strada...
: 1978-1988 - Fiat Punto Mk IFiat PuntoThe Fiat Punto is a supermini produced by the Italian manufacturer, Fiat, since 1993.-1st generation :Internally codenamed Project 176, the Punto was announced in September 1993 and launched in late 1993 as a replacement for the ageing Fiat Uno. The Fiat Punto was voted European Car of the Year...
: 1993-1999 - Fiat UnoFiat UnoThe Fiat Uno is a supermini car produced by the Italian manufacturer Fiat. The Uno was launched in 1983 and built in its homeland until 1995, with production still taking place in other countries.-First series :...
: 1983-1989 - Fiat TipoFiat TipoThe Fiat Tipo is a small family car designed by the IDEA design house and produced by the Italian manufacturer Fiat between 1988 and 1995.The Tipo was initially available only as a five-door hatchback. The car was made entirely out of galvanized body panels to avoid rust, and was built on a...
: 1988-1995 - Fiat TempraFiat TempraThe Fiat Tempra is a small family car produced by Italian automaker Fiat from 1990 to 1998. The Tempra was intended as a replacement for the Fiat Regata. The original project was called Tipo 3, being a mid-size car between the Fiat Tipo and the bigger Fiat Croma...
: 1990-1995 - Fiat X1/9Fiat X1/9The Fiat X1/9 is a two-seater mid-engined sports car designed by Bertone and manufactured by Fiat from 1972-1982 and subsequently by Bertone from 1982-1989....
: 1972-1989
Lancia
- Lancia DeltaLancia DeltaThe Lancia Delta is a small family car produced by Italian automaker Lancia with the first generation being produced between 1979 and 1994, the second generation running from 1993 until 1999, and the third generation Delta entering production in 2008. It was first shown inFrankfurt Motor Show in 1979...
: 1979-1994 - Lancia PrismaLancia PrismaThe Lancia Prisma was a midsize car built by Lancia in the 1980s. It was basically a sedan version of the Lancia Delta, and like its smaller hatchback "brother", shared its chassis and engines with the Fiat Ritmo and Regata...
: 1980s - Lancia DedraLancia DedraThe Lancia Dedra is a compact executive car produced by the Italian automaker Lancia from 1989 to 2000. It was initially designed to support, and later to replace, the Prisma that, six years after its launch, was having difficulties to keep in pace with its latest opponents...
: 1990-1998
Zastava
- Yugo 55
- Yugo 60
- Yugo 65
- Zastava 101
- Zastava 128
- Zastava Florida
- Yugo sana 1.3 1.4
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 fuel 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.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 mm or 40 mm, the larger 44-DCNF is deemed too large for the engine. Both 40-DCOE and 45-DCOE are commonly used where space allows.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 MegaSquirtMegaSquirt
MegaSquirt is the registered trademark of an aftermarket electronic fuel injection controller designed to be used with a wide range of spark-ignition internal combustion engines It is a complete standalone fuel injection controller with software and hardware, developed by Bruce Bowling and Al...
) 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. 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.Production
| Profile | Duration (degrees) | Overlap (degrees) | Lift (mm) | Clearance (mm) Inlet/Exhaust | Application |
|---|---|---|---|---|---|
| 12/52-52/12 | 244 | 24 | - | - | 1.1 L 128 - European Specification |
| 10/54-54/10 | 244 | 20 | - | - | 1.1 L 128 - North-American Specification |
| 24/68-68/24 | 272 | 48 | 9.85 | - | 128 Rally |
| 24/68-68/24 | 272 | 48 | 9.85 | - | 1300 X1/9 - European Specification |
| 10/54-54/10 | 244 | 20 | - | - | 1300 X1/9 - North-American Specification |
| 12/52-52/12 | 244 | 24 | - | - | 1300 X1/9 - Australian Specification |
| 24/68-68/24 | 272 | 48 | 9.9 | - | 1500 X1/9 - European Specification (carb) |
| 10/54-54/10 | 244 | 20 | - | - | 1500 X1/9 - North-American Specification (FI) |
| 10/54-54/10 | 244 | 20 | - | - | 1500 X1/9 - Australian Specification (carb) |
| 9/39-31/1 | 228-212 | 10 | 8 | - | 1.3 L Uno |
| 0/30-40/10 | 210-230 | 10 | 8 | - | 1.3 L Uno Turbo |
| 14/36-44/6 | 230 | 20 | 8.8 | - | 1.4 L Uno Turbo |
Tuning and modification
| Manufacturer | Profile name | Profile | Duration (degrees) | Overlap (degrees) | Lift (mm) | Clearance (mm) Inlet/Exhaust | Application |
|---|---|---|---|---|---|---|---|
| Kent | FT7 | 35/67-67/35 | 282 | 70 | 10.33 | 0.20 / 0.20 | NA - fast road |
| Kent | FT8 | 52/76-76/52 | 308 | 104 | 10.82 | 0.20 / 0.20 | NA - race |
| Piper | BP270 | 33/67-67/33 | 280 | 66 | 9.80 | 0.20 / 0.20 | NA - fast road |
| Piper | BP285 | 36/72-72/36 | 288 | 72 | 10.40 | 0.20 / 0.20 | NA - fast road |
| Piper | BP300 | 39/71-71/39 | 290 | 78 | 11.18 | 0.25 / 0.25 | NA - race |
| Piper | BP320 | 53/83-83/53 | 316 | 106 | 11.18 | 0.25 / 0.25 | NA - race |