Fiat Twin Cam engine explained
Designed by Aurelio Lampredi the Fiat Twin Cam (also known as the Lampredi Twin) 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 shares a lot of parts and most dimensions with the pushrod Fiat 124 series engine (later also available with an overhead camshaft). As the name implies, it was a DOHC design, which was quite unusual in the late 1950s. 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, Morgan and Alfa Romeo cars.
The engine has four cylinders , an engine block from cast iron with five-bearing crankshaft and a cross-flow - cylinder head made of aluminum with two overhead camshafts. The two camshafts act via tappets on the V-shaped valves and are driven by a toothed belt. The engine was developed under the direction of Aurelio Lampredi , initially as an 8-valve version and later as a 16-valve version. Numerous vehicles of the Fiat Group were equipped as standard with the twin-cam engine.
The engine also celebrated success in racing: overall, he won between 1977 and 1992 eleven titles in the World Rally Championship , 1980 and 1981, the Brand World Championship Group 5 , as well as other titles at the national level. The Fiat twin-cam engine is thus the most successful rally engine in history.
The DOHC engine featured a novel and Fiat patented valve timing methodology: the tappets had direct contact with the valves, and the spacers needed to adjust the valve lash were at the top of the tappets with contact with the camshafts. As a result, the ram only had to be pressed down with the aid of a special tool, the spacer plates could then be removed with needle-nose pliers and inserted. The necessary in the hitherto conventional constructions such as Jaguar or Alfa Romeo expansion of the camshaft to get to below the pushrods lying on the valves distance plates omitted. This very simplistic maintenance design was also used in the Fiat 128 and laid the foundation for the triumph of OHC and DOHC engines in everyday and mass production cars. She encouraged many other companies to bypass the Fiat patents with their own designs, but ultimately this setting method prevailed until the widespread introduction of hydraulic valve clearance compensation.The Lampredi four-cylinder always had a three-piece cylinder head in the originally exclusively manufactured 8-valve version: a casting carries the combustion chamber calotte and valve guides, valves and springs, two separate parts each carry a camshaft. This design greatly simplified manufacturing compared to other DOHC designs
.In the 1970s, a four-valve cylinder head was developed for the Fiat 124 Spider Abarth used in rallying. This was one-piece and had a very narrow valve angle, which is why the camshafts had to be removed in order to get at these screws for the then still usual during maintenance work tightening the cylinder head bolts. This high level of maintenance was acceptable because the few vehicles so equipped were in the hands of the factory team in the sport and did not come into the customer's hands. For later use of the four-valve Lampredi engine in the Fiat 131 Abarth Rally, this cylinder head was revised and provided with a larger valve angle to allow retightening the cylinder head bolts without disassembling the camshaft. This change was introduced Since the 400 built vehicles of this type also came into the customer's hands and you did not want to expect the customer to maintain high maintenance. This engine was then charged, used in the Lancia Rally 037.
All previously built Lampredi engines had in common that with longitudinal installation the inlet side in the direction of travel left and the exhaust were on the right or that with transverse installation as in Lancia Beta, the engine against the direction of 20 degrees was tilted backwards and the inlet to the radiator grille and the outlet to the bulkhead showed. The engine was fundamentally redesigned for use in the Lancia theme and Fiat Croma for the first time. The engine received a new, now one-piece cylinder head without separately removable camshaft housing and the installation position was changed so that the engine was tilted forward by 15 degrees in the direction of travel - there was no longer a longitudinal installation of this engine variant. At the same time, the flow direction was changed so that the inlet towards the bulkhead and the outlet towards the radiator grille showed. In addition, the engine block was redesigned to allow the use of two balance shafts used on some variants. For this engine, a one-piece four-valve cylinder head was later developed, which had nothing to do with the old sports cylinder head and was used in vehicles such as the Lancia Thema 16V, the Fiat Tipo Sedicivalvole, the Lancia Integrale 16V. The last variant built by the Lampredi engine was a 1.6-liter four-valve engine used in the Fiat Bravo / Brava until the year 2000. which had nothing to do with the old sports cylinder head and was used in vehicles such as the Lancia Thema 16V, the Fiat Tipo Sedicivalvole, the Lancia Integrale 16V. The last variant built by the Lampredi engine was a 1.6-liter four-valve engine used in the Fiat Bravo / Brava until the year 2000. which had nothing to do with the old sports cylinder head and was used in vehicles such as the Lancia Thema 16V, the Fiat Tipo Sedicivalvole, the Lancia Integrale 16V. The last variant built by the Lampredi engine was a 1.6-liter four-valve engine used in the Fiat Bravo / Brava until the year 2000.
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.
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.
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. This meant considerably improved fuel mileage.
|Displacement (cc)||Bore (mm)||Stroke (mm)|
|1297||76||71.5||Lancia Beta, Fiat 131 Supermirafiori|
|1367||78||71.5||Lancia Beta, Fiat 131 Supermirafiori|
|1438||80||71.5||Fiat 124 Special T/Coupe/Spider|
|1585||84||71.5||Fiat 131 Supermirafiori/Argenta/Ritmo 105TC; Lancia Beta/Delta GT/Delta HF/Prisma|
|1592||80||79.2||Fiat 124 Special T/Coupe, Fiat 132; Lancia Beta|
|1608||80||80||Fiat 124 Coupe/Spider, Fiat 125|
|1756||84||79.2||Fiat 124 Coupe/Spider/132/Tipo/Tempra; Lancia Beta/Delta/Prisma|
|1995||84||90||Fiat Spider 2000/132/Argenta/Strada/Ritmo/Regata/Croma/Tipo/Tempra; Lancia Beta/Delta/Prisma/Thema|