German Car Forum

I have compared the RS4 and the R8 and there engines.
What i noticed is that the weight
(RS4=1650kg, R8=1560kg)
of the rs4(B7) is more but it consumes less fuel
(combined: RS4=13,7l/100km, R8=14,6l/100km)
and the emmissions are alsolower
(RS4=329g/km, R8=349g/km).
But the power outputs are the same 420ps and the torque also 430Nm.

How does this come?

Anyone an idea?

The engine mapping for the R8 is more aggressive, and therefore consume more fuel.

There are other differences between the 2 engines, like the R8 one has dry sump lubrication. I don't know what that means for fuel consumption.

I think the engine in the RS4 has a wet slump while the one in the R8 has a is dry slump setup. That shouldn't really matter with the power output and pollution levels though.

They Rs4 will use stronger components to deliver the power to the wheels 9So the toque doesn't snap the drive train and prop shafts) because the car is obviously heavier.

As for the emissions the Rs4 is again heavier so it uses more power to move it leading to more emissions

Just my guess, dunno if its right tho!

All high end performance cars designed to be fast rather than boulevard cruisers use dry sump lubrication meaning that the engine has an external instead of an oil pan below the crank shaft that is prone to performance loss during heavy braking when the oil can be pushed to one side of the pan putting a temporary choke hold on the engine circulation.

Hot damn that's a long sentence. As a header the 997 Turbo, GT3 and GT2 all use dry sump lubrication. Martinbo shall soon come and join the discussion as this is his field of expertise. But in the end the engine mapping plays the biggest role in this case.

I have to admit I am not sure about the torque biasing wrt to front/rear distribution however if there is difference in the bias it also affects the consumption and carbon emission numbers.
The other thing that is important is where the engine is located at.
In the case of the R8, engine is located at the rear of the car which does affect the effective torque down to the wheels consequently the torque losses hence your consumption figures.

It is late for me and I just got back from a party.I will have to give you a coherent response tomorrow.

Automobile did an article a while ago on the engine in the RS4 and R8. Here is the dyno chart.


Basically the RS4 has more torque at lower rpm, and the torque is more evenly spread across the rpm range. The engine in the R8 is a bit peakier, and it produces 7 extra hp at 250rpm higher then the RS4. The difference is probably caused by the different air intake of the 2 engine. The RS4 has a longer engine air intake which helps to give it more torque at lower rpm.


Have a read here
Dyno Test: 2008 Audi R8 vs. 2007 Audi RS4 - Latest Features, Tests, and Comparisons - Automobile Magazine

I think a nicely warm synthetic engine oil is thin enough and it won't have a noticeable impact on the loss of engine performance during sudden movements of the car, and the crankshaft should have enough momentum to over come whatever resistance effect the engine oil has on it.


Looking at the similar power and torque curves of the two engines, I think the engine mapping is pretty much the same for both of them. I guess the gear ratio would be the biggest factor in determining the the fuel consumption of each car, and generally the more fuel you use, the more C02 emissions you get.

Also don't forget that exhausts and catalytic convertors have a direct bearing on emissions. It's possible that the R8 features freer-flowing (maybe even smaller?) catalytic convertors for enhanced exhaust note. A small difference in the Cat makes for a significant difference in emissions.

Fascinating topic this. I've been doing some reading...

Interestingly, according to KM77 (their info is always nothing less than straight out of the manufacturers' press release manifests) the R-Tronic version uses 13.6L/100 km versus the manual's 14.6L! That's very interesting because the R-Tronic gearbox is simply an automated manual.

So what is it Audi gurus? Heavier flywheel/clutch plate in the manual to handle the "driver factor"?

Edit:

The wind resistance factor is also negligible. The RS4 has a drag co-efficient of 0.34 and a front area of 1.99 sqm resulting in a resistance factor of 0.68. This play the RS4 with 0.31, 2.17 sqm respectively giving a factor of 0.67 - only ever-so-slightly better.

We could debate the differences in the AWD systems until the cows come home... and it would be interesting to see where the RS4's AWD system is more efficient than that in the R8 - if at all...

Here are some nice diagrams showing the AWD and Engine layout of the R8.



Note the spindly, off-centre propshaft coming through the sump and the offset of the main propshaft angle to the front differential.


Gearbox internals showing main rear differential (which gets 90% of torque in static conditions) and how drive is sent to the front wheels.


This pic shows where the propshaft emerges from the sump.


This is the front axle with the viscous coupling ahead of the front differential. This VC can only send a max of 35% of torque to the front wheels


...and this pic shows the R8's complex exhaust and catalytic convertor arrangement

I'm looking for a nice plan view (overhead shot) of the S4/RS4 drivetrain.
If anyone could post it here it'd be nice for comparative purposes...