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== The New 5-Liter 8-Cylinder Engine with 4-valve technology for the Mercedes-Benz 500 SL ==
From Jürgen Frey, Rolf Ohlendorf, and Hans-Jürgen Strauber Mercedes- Benz AG - Dept. EP/MVO

ABSTRACT

The 5-liter V8 light-alloy engine presented by Mercedes-Benz in the new 500 SL at the motor show in Geneva in March 1989 is a new development on the basis of the 8-cylinder engines which have proved themselves for many years.

For this engine, Mercedes-Benz have used a 4-valve light-alloy cylinder head designed in accordance with the most up-to-date features; it has two overhead camshafts per cylinder bank with bucket-type tappets and hydraulic valve clearance compensation. For the first time an electronic/hydraulic adjustment of the intake camshafts is used on a 4-cylinder engine.

This provided the basis for outstanding torque and performance characteristics, stable and smooth idle even at low engine speed. and favourable emission values and fuel consumption figures.

Since the engine consists to a large degree of light alloy, and the power output gained is considerable. it has been possible to attain a weight to power ratio of less than 1 kg/kW.

A NEW ENGINE DEVELOPMENT with 4-valve technology, on the basis of the 8-cylinder aluminium engine which has proven its worth for many years now. was implemented for the 500 SL. This new development is described below.

With the given size framework of the very compact sports car, particular attention had to be paid to a space-saving arrangement for all components. The newly developed 4-valve light-alloycylinder head with two overhead camshafts per cylinder bank, bucket tappet. hydraulic valve clearance compensation and variable intake valve timing was developed specifically for a narrow overall width.

It was thus possible to retain the overall width of the previous 2-valve per cylinder engine. 

An electronic/hydraulic variable intake valve timing system was used for the first time on this 4-valve engine. This provides the precondition for above-average torque and performance, stable, smooth idling even at very low engine speeds, and favourable exhaust gas and fuel consumption figures.

Consistent use of light alloy on the engine and the high power output of 240 kW produces a weight-to-power ratio of less than 1 kg/kW.

The scope of maintenance was reduced further by introducing the single-belt drive which has proven its worth on other Mercedes-Benz engines, hydraulic valve setting, the easy-to-service oil filter arrangement and other facilities to make maintenance simpler.

Mercedes-Benz has further developed the tried and tested 8-cylinder aluminium engine which was presented in 1978 and approx. 500 000 of which have been built to date, for the new SL successor model. and has incorporated a future-orientated 4-valve system with hydraulic valve clearance compensation.

The demanding technical concept of the new roadster necessitated an 8-cylinder engine with the following aims:

- high torque over "the entire engine speed range

- high power output

- comfortable idling behaviour even at low idle speed

- long service life and good serviceability

- further reduced scope of maintenance

- improved exhaust gas raw emission with high economy

- compact engine design. 

The most important data of the engine

are summarized in Table 1.
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