Fiat SOHC - Design and Production

Design and Production

The engine was designed as a transverse 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 driveshafts (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.