Glisse

That the C8 S models were going to use the EA838 2.9 litre TT has been known for many months. The rumours had been floating around for almost as long that Europe would be using diesel engines.

The S4 and S5 will be using the same diesel engine when they are re-released, which will probably be soon. The SQ5 has already been re-released in Europe in the last couple of weeks, and is also using this 350hp / 700Nm diesel. it is quicker than the gasoline SQ5. But the horror for the European forums is that the S6 / S7 is using the same engine as the S4 / S5, and it offers no apparent performance advantage over the previous A6 / A7 models that used the 3.0TDI TT, and would seem much slower, at least in the 0-100km/h metric, than the old model. Whatever the impact is of the electric compressor being used in the C8 models, it isn't obvious from the numbers.

I think your timing is right, AMG cannot continue with the V8 for much longer, outside highly specialised models. But then they don't actually sell so many of those, and those sales are biased to the US.

superswiss

It sounds like both the gasoline C8 S and the diesel get the electric compressor and MHEV system, so yes, the European model being 100hp down over the old one is quite something. The compressor will merely make the powertrain more responsive down low, but from reading the announcement, the max torque still only comes in at 2500 rpm. The MHEV would add power, though. It's not quite clear if the rated power is just the engine or engine + MHEV. The whole thing seems like a scramble to get something compliant to the market with existing engines. Been checking audi.de and one has to wonder what they are smoking. Some of the text is just hilarious like the section titled "Beeindruckende Leistung" (Impressive power). You've gotta be brand new to Audi and know nothing about the C7 to find this impressive.

ONI1013

As of March 11, 2019, seems any rumors of S6 Avants greenlit to come over to US has been squashed (at least for the moment). Audi apparently are still researching and deliberating the profitability of bringing them over. https://www.motorauthority.com/news/...us-coming-soon

Glisse

No, the MHEV in these does not add power, it is used for coasting. The electric compressor adds 7 kW, but this is only under low loads and will never be produced when the combustion engine is making full power, so it is not additive, unlike Mercedes' system on the new straight 6. The benefit seems specifically throttle response. They are implying that the EPC will also be used on the gasoline engine. They are quoting same power and torque as in the RS4/RS5, but should feel a bit sharper, counterbalanced against more weight.

Good pick up on the 2500rpm torque level. The 3.0TDI (any of the 3 versions) in the previous series reached max torque at 1350rpm. Per Euro 6D-temp, Audi are torque cutting the engine at lower rpm within D mode to improve WLTP test numbers, and it makes the car unpleasant to drive. They had been getting forum and media backlash on this too - it seems expedient engineering. Never would have happened in the Piëch era.

I agree with your thought that this seems a bit disorganised. Audi had designed much of this system in 2014, when they still had some decent engineers. They produced a B8 RS5 TDI in this configuration, which was driven by various media. I think they had trouble at board level deciding which way to go in Europe. Risk Audi brand values, or risk fines from not meeting their Euro CO2 fleet targets. That they chose the latter tells you a lot about the current management and board members.

Despite all that, the new C8 S6 and S7 have the potential to be a pretty good drive. Not as soft as the older model, which IMO was too soft for an S car. Hope for those in the US that Audi of America don't make a unilateral decision to fit the comfort oriented air suspension as standard, and not provide the S adaptive suspension.

ONI1013

Not sure what you meant by “does not add power.” But seems the MHEV does add a boost in response time and power, and not just coasting.

“Audiphiles will recognize the 2.9-liter mill from the RS 5. However, response has been improved even further with the addition of an electric compressor. This sits in the air path downstream of the intercooler, close to the engine, and works like a supercharger or turbocharger.

But because it relies on an electric motor (rated at 10 horsepower) to spin the compressor wheel and develop boost pressure, as opposed to an engine belt (supercharger) or exhaust gases (turbocharger) that require engine revs, the electric compressor is always ready to spool. Audi claims boost comes in as little as 250 milliseconds.” https://www.motorauthority.com/news/...urbo-v-6-power

”The electric compressor is the ideal assistant for the turbocharger. It helps out whenever the exhaust gas flow provides too little energy to drive the turbocharger, i.e. when starting off and accelerating in the low-rev range up to 1,650 rpm. High torque is available immediately with no turbo lag whenever the driver needs it, whether starting off, passing or exiting a curve. In everyday driving situations, the early and rapid torque development made possible by the technology keeps revs and fuel consumption low.
If the load demand from the accelerator is high but there is still too little boost from the turbocharger, the EPC comes into play. A compact electric motor with an output of 7 kW accelerates the compressor wheel to 65,000 rpm in roughly 300 milliseconds, producing a relative boost pressure of 1.4 bar.” https://www.greencarcongress.com/201...2-audisq5.html

superswiss

The above doesn't describe the MHEV system. It describes the electric turbo charger and yes we've agreed that it adds a bit of power, but only down low where the engine makes little torque and power, so it helps with the responsiveness. The MHEV system is an additional electric motor that sits between the engine and the transmission and can drive the car fully electric if the engine is turned off. Audi only uses it when coasting, by turning off the engine and then coasting fully electric. Mercedes has a similar system in their 53 models, but they actually use it to add extra power simultaneously with the engine in addition to fully electric coasting and city driving. It appears US models with the 2.9TT are only getting the electric turbocharger, but not the MHEV system.

ONI1013

You’re differentiating the electric compressor as distinct, but in fact, it is all part of the MHEV system. “The 48-volt main electrical system (MHEV) includes an electric-powered compressor (EPC) and a mild hybrid system.” “Power for the electric compressor comes from a 48-volt mild-hybrid system”
https://www.greencarcongress.com/201...2-audisq5.html; https://www.motorauthority.com/news/...urbo-v-6-power

superswiss

True, now that I think about it some more it's gonna have to have both. The EPC requires the 48V system, which in turn requires the motor between engine and transmission to charge to the battery, but the main point is that Audi doesn't appear to use the system to add power at the top end like Mercedes and others do. Only the EPC is used to improve low end performance, and the rest of the system is for efficiency only to save fuel while coasting.

ONI1013

Yep, only the lower end performance and slightly improved efficiency— which I think overall, is more important for most drivers. No one hardly reaches top end speed during “normal” street/highway driving (at least not in the US).

But I do have to admit, I do find it impressive they managed to squeeze the same 450 HP/442 ft-lb torque just from a 2.9L V6 Twin-turbo as they did from the previous a 4.0L V8 Twin-turbo EU model.

Glisse

I'm not convinced that the 2.9 litre TT V6 engine will have the EPC. It was just a throw away line right at the end of the press release which was focussed on the diesel version. Could have been a mistake, although it is being widely reported. Difficult to see, in engineering terms, how they can easily marry the EPC with the B-cycle variable timing, and more particularly, the variable compression. The whole point of the B-cycle is to provide improved efficiency and response at low engine loads.

There is a new low output V8 version within the updated engine range. Porsche are using it in the Panamera GTS, where it makes 450hp. Audi have chosen not to use this - it contributes 235g/km of CO2 on the WLTP combined cycle. The 2.9 as fitted in the RS5 (without any test cycle benefits from their PHEV system) contributes 206g/km CO2. The 2.9 fitted in the Panamera 4S, which has very similar performance to the GTS, is rated at 191g/km.

The Panamera 4, which uses the same 3.0TFI turbocharged engine as the C8 A6 55, and is fitted to the S4/S5 (at a slightly higher state of tune) is rated at 194g/km. The A6 was rated at a range of 156-164g/km under NEDC test cycle. Under WLTP, it goes up to199-215g/km. That's a big jump, same thing happened with the 3.0TDI. There is a direct correlation between C02 contribution and fuel consumption - 215g/km is 25mpg in the US.

But the further madness here is that the new 3.0TDI with EPC, as already in the SQ5, has a Euro 6D-temp WLTP rating of 213g/km. Which is higher than the 2.9 litre TT.