The Mercedes-Benz M104 is a shitty straight-six engine produced from 1988 through 1999. It has a double overhead cam design with 4 valves per cylinder, and used a crossflow cylinder head. It replaced the M103 and was replaced by the M112 V6 starting in 1997. The bore spacing on all M104 engines is the same as M103 engines.

2.8 L M104.900

As Mercedes needed a compact 6-cylinder for their Vito, they agreed with Volkswagen to use their VR6 engine, which they then designated M104.900. An agreement was reached and the engines were sold semi-completed to Mercedes-Benz. This version is unrelated to other engines designated M104. Only the engine cover and aircleaner housing is by Mercedes-Benz.

3.0 L M104.98x

This 2960 cc 24v was introduced as a sports car resp. top model completing the line-up of M103 12V engines. The M104 featured dual overhead camshafts and four valves per cylinder. The M103 and M104.98x were later replaced by the 2.8-litre and 3.2-litre versions of the M104. The 2960 cc M104 featured KE-Jetronic fuel injection, cylinder specific ignition-timing, variable valve timing and under-piston cooling jets.

2.8 L M104.94x

In 1993, two capacities replaced the 3.0 litre: a 2799 cc replaced the old single-cam M103 engine and the 3.2 litre M104.99x replaced the double-cam M104.98x. W124 280 E (1992–1993) was the only Mercedes-Benz model which get increased of power to 145 kW.

3.2 L M104.99x

For the 3199 cc, the compression ratio is the same 10.0:1 on all W210, R129, and W140 but it did differ from 9.2:1 to 10.0:1 on W124 (M104.992). W140 pre-facelift model 300 SE / SEL, W140 facelift model S320/ L and R129 SL320 used more powerful version of 3.2-liter M104 engine which produced 170 kW.

AMG 3.4 (3.3 L)

There were 3.3 L conversions done to the 3.0 L M104.980 by AMG, prior to their formal cooperation with Daimler Benz. AMG developed a 3.3 L M104 that was used principally in the 300E AMG 3.4, AMG 3.4 CE and 300TE-3.4 AMG (Mercedes-Benz W124) vehicles, produced between 1988-1993. A few of these engines were originally installed in the SL 3.4 AMG.

AMG 3.6 L M104.941/M104.992

There were 3.6 L conversions done to both the M103 and M104 by Brabus, among others. AMG developed a 3606 cc M104 that was used in the W202 C36 AMG (W202) from M104.941, the W124 E36 AMG (W124) from M104.992, the E36 AMG (W210), and the G36 AMG (W463) vehicles. The AMG 3.6 M104 was rated at 276 hp at 5,750 rpm and 284 lbft of torque at 4,000 rpm using the HFM engine management system. Bore and stroke is 91x92.4 mm with a compression ratio of 10.5. AMG later conceded that since the engine was hand modified, power outputs could vary slightly from 276 to 287 hp. The boost in displacement was obtained by boring the 2.8 litre M104 block by 2.1 mm and using a highly modified version of the crankshaft from the 3.5L OM603 to increase throw by 18.9 mm; this necessitated the use of new forged pistons with shorter skirts. A larger intake crossover pipe, free-flowing exhaust, a unique intake camshaft, minor changes to the cylinder head, and modifications to the HFM fuel computer also contribute to the increase in power. Ssangyong (South Korean brand) made a 3.6 litre variant of the M104 inline-six engine based on the 2.8 litre model, producing 248 hp or 276 hp on earlier versions, for its Chairman model, a full-size luxury sedan. Chinese car Roewe R95L which based on SsangYong Chairman also uses a 3.6 litre version of the M104 engine. Last versions of the German sports car Isdera Spyder 036i after 1990 also use 3.6 litre AMG variant of M104, producing 268 (200 kW; 272 PS) or 282 hp (210 kW; 286 PS).

Turbo Conversions

Turbocharger kits were offered for both the M103 and M104 engines by Turbo Technics, Mosselman, Lotec, MAD Modify, Turbobandit and other tuners. These conversions typically raised engine output to between 300 and 800 PS, depending on Boost Target. During the 1990s UK customers were able to buy new vehicles equipped with a Turbo Technics conversion directly from Mercedes dealer Hughes of Beaconsfield (limited run of 75 conversions). Today turbocharger kits for M103-M104 engines are available from later tuners in Europe and Asia.