Boring Technical Stuff
Posted: Sun Dec 08, 2019 3:06 pm
I never paid much attention to the C8 RS6 when it was launched, assuming it was just a re-skin of the C7 with some more technology. There's a bit more to it than that though.
The Audi website had little to say about the engine apart from the addition of mild hybrid capability. However the pictures were a bit more interesting. The C7 (first picture) had a hot inside-V turbo layout, and a right dog's dinner it was. Audi abandoned side mount intercoolers and went for a single water cooled charge cooler in the front of the V. That pushed the turbos to the back of the V. Everything was compromised - the intakes were restrictive, the charge cooler was small and a long way from the inlet manifolds, and the exhaust and catalysts were tied up in a reef knot.
I assumed the C8 (second picture) was the same, but it isn't, and I haven't read a single word about it anywhere. Audi retained the hot-inside-V turbos, but went back to large 22-row side mount intercoolers, which sit close the inlet manifolds of course. It frees up space inside the V, the turbos move forwards to the centre (like everybody else's V8's), leaving room for the catalysts at the back of the V. The exhaust downpipes now resemble uncooked spaghetti, rather than cooked, and the air filter appears to sit on top of the radiator, with short, straight inlets to the turbos. It looks very much better than before.
The peak power is no higher than before, but torque is higher, and that gives more area under the power curve, which helps acceleration. I think transmissions are part of the answer. When the C6 RS6 and Bentley Continental were launched, they were limited by the torque capacity of the 6-speed 6HP26 gearbox. I believe the C7 used the 8HP55 which allowed Audi to use more boost. Since then, large capacity super-and turbo charges engines have become the norm, and ZF now make the 8HP90 with even more capacity. That allowed Audi to dial the torque up to 800Nm, and acceleration benefits (or it would if the car wasn't heavier). Anyway, it all looks more tuneable than before.
Nick
The Audi website had little to say about the engine apart from the addition of mild hybrid capability. However the pictures were a bit more interesting. The C7 (first picture) had a hot inside-V turbo layout, and a right dog's dinner it was. Audi abandoned side mount intercoolers and went for a single water cooled charge cooler in the front of the V. That pushed the turbos to the back of the V. Everything was compromised - the intakes were restrictive, the charge cooler was small and a long way from the inlet manifolds, and the exhaust and catalysts were tied up in a reef knot.
I assumed the C8 (second picture) was the same, but it isn't, and I haven't read a single word about it anywhere. Audi retained the hot-inside-V turbos, but went back to large 22-row side mount intercoolers, which sit close the inlet manifolds of course. It frees up space inside the V, the turbos move forwards to the centre (like everybody else's V8's), leaving room for the catalysts at the back of the V. The exhaust downpipes now resemble uncooked spaghetti, rather than cooked, and the air filter appears to sit on top of the radiator, with short, straight inlets to the turbos. It looks very much better than before.
The peak power is no higher than before, but torque is higher, and that gives more area under the power curve, which helps acceleration. I think transmissions are part of the answer. When the C6 RS6 and Bentley Continental were launched, they were limited by the torque capacity of the 6-speed 6HP26 gearbox. I believe the C7 used the 8HP55 which allowed Audi to use more boost. Since then, large capacity super-and turbo charges engines have become the norm, and ZF now make the 8HP90 with even more capacity. That allowed Audi to dial the torque up to 800Nm, and acceleration benefits (or it would if the car wasn't heavier). Anyway, it all looks more tuneable than before.
Nick