A Bit of TDI Racing History

Thats a very good read. I cannot believe boost pressures in the range of 40psi!!!! incredible.

2 bar relative boost is only 29 PSI.

They said 2800mbar


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They said "2800 mbar absolute" (2012-2013) and "2960 mbar absolute" which is ~28.4 psi depending on the track altitude.

Ohh absolute. I had my hopes up. Woulda been hilarious for 40psi.


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40psi is no big deal

It is actually big deal to do it over 24 hours. In addition, because a restrictor is placed upstream of the compressor inlet, the compressor will operate at a higher pressure ratio than its absolute boost pressure would suggest. This actually can be calculated quite readily. The pressure of a choked throat will be ~0.53X that at the ambient entry. So 3 bar absolute pressure would actually represent a map PR of close to 6. Big deal indeed.

This is true...

TDIMeister said:

This actually can be calculated quite readily. The pressure of a choked throat will be ~0.53X that at the ambient entry. So 3 bar absolute pressure would actually represent a map PR of close to 6. Big deal indeed.

Click to expand...

A clarification is in order. This remains true for static pressure, but most compressor maps -- at least those from Garrett -- are T-T (total-to-total). The static pressure may be at 0.53 bar at the throat of the restrictor, but it will be at Mach 1 at the same spot and the total stagnation pressure remains constant at ambient minus pipe losses. There is some recovery of static pressure in the diverging section of the restrictor as the velocity simultaneously declines.

The overall point remains sound, however: 24 hour endurance racing puts enormous stresses on every part of the engine. Audi and other manufacturers have always had the option in the ACO rules to operate with smaller displacement engines but at higher boost allowance but didn't do so; rather, in the early years of the Diesel era, both Audi and Peugeot maxed out on displacement at the significant cost of weight and packaging, because it was concluded that relatively low BMEP rather than highly stressed, high-strung engines were required to last the duration of the race.

This paper goes explains the design rationale for the LeMans V12 TDI
http://bit.ly/1qoxsQJ

Naturally, there have been 8 years of development and the latest engines make about the same power with half as many cylinders, much smaller displacement and significantly better fuel efficiency.