Earlier this week I read something about the RS4 actually getting better mileage than the S4 despite it's increased horsepower/torque. How is this possible? I have this feeling I'm missing something obvious but it seems that people's real life mileage runs 20 to 25 on the freeway and 15 to 20 around town... not that it's worth mentioning but they claim 10 to 13 in stop and go traffic. Can anyone explain this to be me please? Thanks ahead of time.

Direct injection is about 5-10% more efficient than standard manifold injection. It's very easy to get 23 mpg on the highway cruising with the RS4.

because I never use the upper gears anymore...

because the RS4 is an FSI engine, but the B6 and B7 S4 engine isn't. So the RS4 had direct injection and lean burn, but the S4 has neither.

your drivng style will have a lot to do with the MPG.

gets better mileage.

I'm not sure about highway mileage.

that it's tuned to work harder in some way.

A highly strung NA engine requires high revs. High revs give you lots of pumping losses and frictional losses.

The most efficient engines are low revving. That goes against getting lots of power from displacement.

it will usually result in better fuel efficiency.

Also spinning the motor faster will net more HP from the same displacement. It will be more thirsty at higher revs, but that's not where you would necessarily cruise on the highway.

I'm not a mechanical engineer, I was just saying that usually when you retune an engine to make more HP without changing it's displacement, it will usually be more fuel efficient as well.

In the RS4's case, it may just be due to the FSI.

that cars are able to get higher and higher HP without fuel efficiency suffering...and in some cases improving slightly. The Corvette is one excellent example.

improvements in intake designs, variable valves, valve ports, timing efficiency, etc are where some of the gains are coming, both for HP and fuel efficiency.

it's what they're striving for...increased HP(or performance) without a cost to gas mileage.

make the engine less efficient.

To make a fair comparison, you need to compare engines using similar technology. Comparing an FSI to a non-FSI engine introduces too many variables.

For example, compare the S2000 engine to a Civic engine. Similar or same sizes, but the Civic is much more efficient (and less powerful).

The same would apply when comparing a BMW 330i to a BMW M3 (3.2).

in the fact that most all mfgrs are constantly getting higher HP but still managing to keep the gas mileage fairly high, which they are mandated to do for stepped EPA fleet average requirements(US market).

it goes hand in hand that efficiency is increasing, in order to be able to accomplish this.

so, i agee with you.

It will change the amount the car uses to go a certain distance though.

If you're just considering the fuel consumption of an engine on a dyno, I'd agree with you.

comparing car efficiency, I suppose I was off the mark there.

Either way, we can agree that the RS4 engine is a fine piece of gear.

=D

true, but aside from gearing, improvements are being made that afford higher and higher HP without MPG suffering, car to car, across the industry. from the Camry to the high performance car, HP is constantly increasing(and in most cases engine displacement).

an easy way would be to put a true OD as your 6th or 5th gear, which would not only make gains at highway speed, but also on surface roads. but they aren't necessarily doing this. they are mainly doing this by further improving engine efficiency.