The normally aspirated 3.8 litre flat 6 engine was designed specifically for the 1993 Carrera RS 3.8 and the Carrera RSR. Both cars were supplied with the wide, Turbo-style body but retained much of the weight reduction features of the original 1992 Carrera RS. The detailed specifications are below along with those for the standard RS for comparison purposes. There is a Car+Driver article on the 964 3.8 RSR here.

M64/03 (Carrera RS)
M64/04 (3.8RS)
M64/04 (3.8RSR)
Bore
100mm
102mm
102mm
Stroke
76.4mm
76.4mm
76.4mm
Displacement
3600cc
3746cc
3746cc
Compression Ratio
11.3:1
11.0:1
11.4:1
Power (PS) @ RPM
260/6100
300/6500
320/6900
Torque (Nm) @ RPM
325/4800
360/5250
360+/6200

The M64/04 engine as fitted to the 3.8RS was fairly well defined but the 3.8RSR engine was much more difficult to pin down. Specifically for racing virtually all the cars were sold to racing teams who invariably put their own expertise to use to get that little "extra" from the car. Depending upon factors such as induction system and a variety of restrictors, power could be as much as 375PS or more.

In common with the 3.6 litre engine, the 3.8 litre unit uses 2 valves per cylinder with a single chain driven overhead camshaft per cylinder bank operating both inlet and exhaust valves via rocker arms, the engine design being heavily based on that of the GT1 racer.

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