Audi throws cloak of secrecy over 4-litre TDI

In an amazing move, of which the KGB or the Mafia would be immensely proud, Audi has declined to disclose the bore and stroke of its new 4-litre TDI diesel engine.

For behind all the PR glitz of the new SQ7 TDI there is a serious side.

The Audi press office declares “We do not communicate bore and stroke.  With 320kW (435hp) and 900Nm (663.8lb-ft) of torque, the new Audi SQ7 TDI is the most powerful diesel SUV on the market”.

The engine has a swept volume of 3.956 litres which suggest it is an eight-cylinder version of the 3-litre V6 TDI which has a swept volume of 2.967 litres.

In fact, when the 2.967 litre swept volume of the V6 is factored up by the ratio of the number of cylinders, the result is exactly 3.956.

So, why all the secrecy? The secrecy, however, extends.

Asked if the new 4-litre has a compacted graphite cylinder block, like that of the larger 4.2-litre V8 – the low-volume (20,000 a year?) blocks are sourced from Bruhl in Germany – the company declined to elaborate.

In reply to our straightforward question: Does the SQ7 TDI engine have a compacted graphite iron vee 8 block, and is this sourced from Tupy in Brazil?  Or from Bruhl in Germany?

The Audi press office offers ”Please understand that Audi do not communicate its suppliers.”

The implication of the bore and cylinder dimensions is obvious. For although Audi describes the 4-litre V8 TDI as “an all-new engine” which has “been newly developed from the ground up” and “combines best-in-class performance with low consumption and guarantees maximum dynamics”, there is the potential for the two engines to share common components, such as pistons.

Many of the five Cs, however, will be different, such as vee block and heads, as well as camshaft and crankshaft, but there is the potentiality for commonality.

Longer term, however, Audi could drop the 4.2-litre V8 as the new engine builds up power and torque.

In the SQ7, the 4-litre develops 109.9PS/litre and 227Nm/litre of torque.

In the Q7 e-tron, the 3-litre engine is described as giving 258bhp and 600Nm of torque.

In the Q7-etron, for example, Audi says “The 3.0 TDI, a highly efficient, latest-generation V6 diesel engine, delivers 190 kW (258 bhp) of power and 600 Nm (442.5 ibft) of torque.”

These are equivalent to 86.9bhp/litre and 202Nm/litre in terms of specific power and torque.

The 4.2-litre TDI engine in the Audi A8 quattro gives 378 bhp (283 kW) of output or 90 bhp/litre and a torque of 850 Nm, equivalent to 202 Nm/litre.

So there is the potential to drop the 4.2-litre engine altogether and replace it with the 4-litre TDI.

It has to be assumed the new 4-litre TDI does have a compacted graphite (CGI) cylinder block.

Last November, Autoweek announced has announced a fix to correct the software in some 85,000 vehicles, some of which were initially named in a Notice of Violation (NOV) issued by the EPA at the beginning of the month. The action followed the reveal of a number of technical solutions to German regulators the previous week, with VW AG announcing that it was presenting for approval the required modifications for a number of diesel engines.

"Audi will revise, document in detail, and resubmit for US approval certain parameters of the engine-management software used in the V6 TDI 3-litre diesel engine," the automaker said in a statement.

"That is the result of the discussions held between a delegation from AUDI AG and the US Environmental Protection Agency (EPA) and the California Air Resources Board (CARB). The updated software will be installed as soon as it is approved by the authorities. The three brands Audi, Porsche and Volkswagen are affected. Audi estimates that the related expense will be in the mid-double-digit millions of euros."

Audi had initially denied that the 3-litre TDI diesel engines, offered in a number of models in North America, contained any kind of software that acted as a "defeat device," but had nevertheless halted sales of new and used models that feature that engine. The affected models included the A6, A7, A8, A8L, Q5 and Q7 models from the 2009 through the 2016 model year, along with the Porsche Cayenne Diesel and the Volkswagen Touareg TDI.