From the listing for this Classic 70’s Porsche 935 K4 Race Car for sale:

Porsche 935k4 race car, this was a 79 K3 that was re-shelled in 81 to be a K4. The car is a tube framed K4 race car, which could be homologated as a Moby dick replica. The work was carried out by DP who make the bodies for Kremer . The car has the correct flat fanned 935 engine producing 680BHP in a car that weighs under a ton, everything about the car is correct, including the titanium drive shafts, It has air jacks, centre lock wheels, spare springs and BBS wheels. Not been raced since last rebuild and in very good order.

From Wikipedia:

935 K3 and K4 by Kremer

1981 Wera Weissberg Team Porsche Kremer 935 K3

As Porsche hesitated to sell their Evolution models, some teams developed their own ideas, especially Kremer Racing from Cologne, Germany. Parallel to the factory in 1976, they had built a 935 K1, and in 1977, modified their customer 935 to the K2. For 1979, they introduced the 935 K3 (for “Kremer Type 3”; the derivative of the successful K2). Driven mainly by Klaus Ludwig, it won the 24 Hours of Le Mans in 1979, beating all prototypes, in heavy rain, which is usually considered a disadvantage for race cars with windshields. Coming in second was a factory spec model, driven by Rolf Stommelen, and supported by team owner Dick Barbour and actor Paul Newman.

Facing strong competition in the 1980 DRM by the big Zakspeed Ford Capri, the K4 was introduced in mid 1981, for 400 000 Deutsche Mark. Porsche supplied an 3,1L engine with 750-800 hp at 1,5 bar boost for 91 000 DM in total.