Originally Posted by wikipedia

190E 2.3-16 valve & 2.5-16 valve "Cosworth"

The Story
Back in the late 1970s, Mercedes competed in rallying with the big V8-powered Coupés of the R107 Series, mainly the light-weight Mercedes 450 SLC 5.0. Mercedes wished to take the 190E rallying, and asked British race car engineering company Cosworth to develop an engine with 320 bhp for the rally car. This project was known as project "WAA" by Cosworth"[2]. During this time, the Audi Quattro with its all wheel drive and turbocharger was launched and made it apparent that the 2.3-16v would not be competitive. With a continued desire to compete in high-profile motorsport with the 190, and also now an engine to do it with, Mercedes turned to the Deutsche Tourenwagen Meisterschaft (DTM) motorsport series instead. Cars racing in this championship, however, had to be based on a roadgoing model. Mercedes therefore had to put into series production a 190 fitted with a detuned version of the Cosworth engine. This high performance model was known as the 190E 2.3-16, and debuted at the Frankfurt Auto Show in September 1983, after its reputation had already been established. Three cars, only slightly cosmetically altered, had previously set three world records in August at Nardo, Italy, recording a combined average speed of 154.06 mph over the 50,000 km endurance test, and establishing twelve international class endurance records.

The Engine
The Cosworth engine was based on the 2.3-liter 8-valve 136-hp unit already fitted to the 190- and E-class series cars. Cosworth developed the cylinder head, "applying knowledge we've learnt from the DFC and BDA"[3]. It was made from light alloy using Coscast's unique casting process and brought with it dual overhead camshafts and four valves per cylinder, meaning 16 valves total which were developed to be the "largest that could practically be fitted into the combustion chamber"[3].

In roadgoing trim the 190E 2.3-16 produced 49 hp (36 kW) and 41 ft·lbf (55 N·m) of torque over the basic single overhead cam 2.3 engine on which it was based. The 2.3 L 16 valve engine made "185 hp (137 kW) at 6,200 rpm and 174 ft·lbf (235 N·m) at 4,500 rpm, the oversquare 95.50 x 80.25 mm bore and stroke dimensions ensuring that it revs easily up to the 7000 rpm redline"[4]. Acceleration from 0-100 km/h (62 mph) was 8.0 seconds, and the top speed was 230 km/h (143 mph)[4].

US-Specification cars had a slightly reduced compression ratio (9.7:1 instead of 10.5:1), and were rated at 167 hp @ 5800 rpm and 162 lb-ft @ 4750.

The roadgoing version of the engine was reconfigured with reduced inlet and exhaust port sizes, different camshaft profiles, no dry sump configuration and Bosch K-jetronic replacing the specialised Kugelfischer fuel injection. These changes helped bring power down to the required 185 bhp specification, but still resulted in a "remarkably flexible engine, with a very flat torque curve and a wide power band"[3]. The heads for the engines were cast at Cosworth's Coscast foundry in Worcester and sent to Germany to be fitted to the rest of the engine, parts of which were different from the standard 2.3 including light pressed alloy pistons, and rings designed to withstand higher engine speeds, whilst con-rods, bearings and bearing caps were found to be strong enough as standard and left unaltered[3].

The 2.5 model
An enlarged 2.5 L engine replaced the 2.3 L in 1988 and increased output by 17 hp (12.5 kW) with a slight increase in torque. For the European market without catalyst the car delivered 202 bhp (150 kW). The catalytic converter was becoming prevalent at this time, and catalyst equipped 2.5-16s produced a slightly reduced 197 bhp. It is a subject of debate whether the 2.5 L engine was developed and built by Mercedes or Cosworth. Mercedes were not keen to broadcast the fact that their most sporting saloon car has an engine developed by a British company. However some cylinder heads from 2.5 L cars are stamped with the Coscast logo indicating they were cast at Cosworth's foundry just like the 2.3s. Cosworth also list a Project code "WAB" for the development of the 2.5-16 cylinder head just as they do for the 2.3-16 cylinder head[2].

16v Differences
Due to their performance status, the 16 valve cars were in some areas very different from the other 190 models. The body kit on the 2.3 16 and 2.5 16 reduced the drag coefficient to 0.32, one of the lowest cd values on a four door saloon of the time, whilst also reducing lift at speed. The steering ratio was quicker and the steering wheel smaller than that on other 190s, whilst the fuel tank was enlarged from 55 to 70 L. The Getrag 5-speed gearbox was unique to the 16 valve and featured a 'racing' gear pattern with 'dog-leg' first gear, left and down from neutral. This meant that the remaining 2nd, 3rd, 4th and 5th gears were in a simple H pattern allowing fast and easy selection. The gearchange quality was, however, noted as "notchy, baulky"[4], criticisms also levelled at the E30 BMW M3 which shared the same gearbox. An oil cooler was fitted to ensure efficient oil cooling for the inevitable track use many of these cars were destined for.

The strictly four-seater interior had Recaro sports seats with strong side bolsters for front and rear passengers. 3 extra dials - an oil temperature gauge, stopwatch and voltmeter - were included in the centre console. The, 190E 2.3-16 was available in only two colours, Blue-Black metallic, and Smoke Silver (which looks gold). The introduction of the 2.5-16 brought along two extra colours, Almandine Red and Astral Silver.

All 2.3-16 valve 190 models are fitted with a Limited Slip Differential (LSD) as standard. They were also available with Mercedes' ASD system which was standard equipment on the 2.5-16v. The ASD is an electronically controlled, hydraulically locking differential which activates automatically when required. The electronic control allows varied amounts of differential lock from the standard 15% right up to 100%. It is not a traction control system however, and can only maximize traction rather than prevent wheel spin. Activation of the ASD system is indicated by an illuminating amber triangle in the speedometer.

The suspension on 16 valve models is very different to the standard 190 (w201). As well as being lower and stiffer, it has quicker dampers, larger anti-roll bars, harder bushings and hydraulic Self-Levelling Suspension (SLS) on the rear. This allows the rear ride height to remain constant even when the car is fully loaded.

At the inauguration of the new, shorter Nürburgring in 1984, a race with identical cars was held, with former and current F1 pilots at the wheel. A rather unknown young driver named Ayrton Senna took First place in that race.

Private Teams such as AMG later entered the 2.3-16 in touring cars races, especially the DTM. In the late 1980s, the 2.5-16 (never released in the United States) raced many times, against the similar BMW M3 and even the turbocharged Ford Sierra Cosworth