4 valves per cylinder, not the cams but that is the reason the mod motor is HUGE in size but small in displacement.
The mod comes/came in SOHC, DOHC, two valve, three valve and four valve versions.
Multiple valves is the only way you can get a small engine to try to get close to a large displacement two valve engine, or as Ford as done add super chargers.
At that, Audi developed a diesel for road racing that worked well---- (Now by this time this road racing class was HEAVILY restricted, i.e. really a spec. class , so those with the most money to make the specs work for them always won. Although one year Roger Penske saw a loop-hole in the rules and beat the Class 1 boys with a Class 2 car. A wonderful -- In your face move.) ---- so it was no longer who had the best engine that won but who had the money and who the rules maker preferred.
Weight
At the beginning of the 2006 season, homologation rules for Le Mans Prototypes (LMP) cars were changed, for the LMP1 class, an increase in minimum weight from 900 kg to 925 kg was mandated. While officially this was to allow closed top prototypes to run with air-conditioning (as this would have added weight over open top cars), some have speculated that this was done at the behest of Audi to allow the R10 to be competitive.[6]
The R10 TDI in the 2006 12 Hours of Sebring was overweight at 935 kg (2,061.3 lb), preventing engineers from using ballast to optimize handling and balance.[7]
Engine
Unlike most racing cars competing in the LMP1 series, the R10 TDI is powered by a diesel engine, with two parallel turbochargers and utilizes the Turbocharged Direct Injection (TDI) technology. The engine block has a displacement of 5.5L in V12 configuration made of aluminium, employing common rail direct fuel injection technology. The turbochargers are supplied by Garrett AiResearch, with 39.9 mm (1.57 in) restrictor plates mounted in front of the intake.
The V12 engine is rumored to weigh more than 200 kg (441 lb).[8] This is heavier than the 130 kg (287 lb) of a concurrent Judd V10, and even the 180 kg (397 lb) of the Ricardo turbodiesel prototype based on it.[9] Audi engineers say that the weight per cylinder is the same as the preceding 3.6-litre FSI V8 of the Audi R8.[10] The wheelbase has been increased over the R8 to 2,980 mm (117.3 in) to accommodate the longer engine.
Even with a larger-than-necessary restrictor plate, the car is rumoured to produce 700 hp (522 kW; 710 PS) in qualification, limited by the fuel combustion quality. This output cannot be maintained in races because it may cause a clogged diesel particulate filter. The peak pressure in the cylinder is probably around 200 bar, compared with 85 bar for an atmospheric petrol engine.
