Fiat Twin Cam engine

Fiat Twin Cam engine
Overview
Manufacturer	Fiat/Lancia
Production	1966–2000

Designed by Aurelio Lampredi, the Fiat Twin Cam (also known as the Lampredi Twin Cam) was an advanced inline-four automobile engine produced from 1966 through 2000 as a Fiat/Lancia engine until it was replaced by the "family B" series of engines. The engine uses the block of the OHV engine found in the Fiat 124 with some modifications to accept the belt drive for the camshafts. The head itself is made in three pieces, one carrying the combustion chamber and valves and one separate casting for each camshaft in tunnel type bearings. The valves had an included angle of 65 degrees. The engine featured a revolutionary new method for adjusting the valve clearance. Usually at that time in DOHC engines like from Alfa Romeo or Jaguar, small shims were placed on the valve stem inside the bucket tappets, thereby necessitating the removal of the camshafts to get access to these shims to adjust the valve clearance, making for time consuming and very expensive maintenance work. Lampredi’s design placed the shims on top of the tappets where they could be removed with the camshaft in situ after the tappets were pressed down with a special tool. This design was patented for Fiat and was used in the engines of the 128 and 130, and even the (Ferrari/Fiat) Dino V6 engine was converted to this system. The engine was produced in a large number of displacements, ranging from 1,297 cc to 1,995 cc and was used in Fiat, Lancia, Alfa Romeo, SEAT and Morgan cars.

Fiat was the pioneer in engine development during the time period, using a monoblock technology, belt driven camshafts and aluminium alloy heads. Earlier Fiat Twin Cam engines were actually O.S.C.A. designs. Curiously, the first directly injected diesel engine in a passenger car, the 1929cc engine powering the Fiat Croma Turbo D i.d, also derives from the Lampredi Twin Cam, despite being a SOHC design.

Applications

Lampredi's Twin Cam engine was first seen in the Fiat 124 Coupé of late 1966, but was later made available in a large number of cars.

Fiat CHT engine in a Croma

One interesting version was the CHT (for "Controlled High Turbulence"). This was mainly used in the first generation Fiat Croma and used auxiliary intake ducts to provide a better fuel and gas mixture under low or partial acceleration.^[1] This meant considerably improved fuel mileage.

Displacements

Motorsport

The Fiat Twin Cam engine has been widely used in motorsport and has been the most successful engine in the history of the World Rally Championship. The World Rally Championship for Manufacturers has been won by Fiat and Lancia, using engines based on the Lampredi Twin Cam engine, for a total of 10 years.

The four valve version made its first appearance in the Group 4 competition version of the Fiat 124 Spider Abarth, where it had 1.8 litres. Group 4 regulations at that time allowed the use of a cylinder head of a “free” design. This engine still used a three piece cylinder head design with an included valve angle of 46 degrees.

In later years motorsport regulations were changed so that the use of four valve heads was only possible when the homologation cars had four valve heads. Therefore, the homologation series of the Fiat 131 Rally Abarth came with a two-litre version of the four valve engine.

In motorsport, this engine was always hampered by some of its old design features. Despite of having a long stroke (84 mm bore x 90 mm stroke) the engine needed lots of revs to deliver sufficient power with a significant lack of torque at lower revs. In that respect the Lampredi engine was always inferior to the contemporary Ford Twin Cam with its Cosworth-developed head with much more modern geometry. In theory, the Fiat engine could have been changed to a much shorter stroke. This would have meant that the cylinder head bolts would need to be moved. These bolts made it impossible to enlarge the engine’s bore and they also were responsible for an unfortunate routing of the intake channels in the cylinder to avoid these bolts. Moving the bolts would have meant developing a new cylinder head. Abarth technicians were on their way to develop a new head when Lampredi found out and made it very clear that he absolutely refused any change to “his” engine.

These engines were later used in the mid-engined Lancia 037, where they were supercharged and eventually enlarged to 2.1 litres.

In addition to the titles in the World Rally Championship, the Fiat Twin Cam equipped the Lancia Beta Montecarlo Turbo, that won the World Sportscar Championship for two consecutive seasons in 1980-1981.

Constructor	Car used in World Championship	Seasons	Manufacturers' Titles
Fiat	Fiat 124 Abarth	1970–1975	—
Lancia	Lancia Beta Coupe	1974–1975	—
Fiat	Fiat 131 Abarth	1976–1982	3 (1977, 1978, 1980)
Lancia	Lancia 037	1982–1986	1 (1983)
Lancia	Lancia Delta HF 4WD and Delta Integrale	1987–1993	6 (1987–1992)

See also

• Fiat Pratola Serra modular engines

Footnotes

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