jersh

So .. I was surprised to learn that the 4.2L v8 in the rs4, which produces about 80 more horsepower than the 4.2L v8 in the a8, is naturally aspirated.

So essentially ... they are the same engine. What explains the fairly wide gap in performance ? Did they just do a bunch of little things like polish and lighten the pistons, etc., etc. ?

I wonder what the penalty for what they did was ... anyone know what gas mileage on the rs4 is ?

Ringmeister

From an Audi press release:

"At the heart of the RS 4 quattro is a naturally aspirated 4.2-litre V8 FSI petrol engine that delivers 420PS, equating to a highly impressive specific output of just over 100PS per litre. Maximum torque of 430Nm occurs at 5,500rpm, and 90 per cent of this peak is available from 2,250rpm all the way to 7,600rpm, though the exceptionally free revving unit is actually capable of powering on well beyond this to 8,250rpm to provide breathtaking acceleration. The 0-62mph sprint is dispatched in just 4.8 seconds, 124mph from rest on a suitable Autobahn can be seen in only 16.6 seconds and an electronically limited top speed of 155mph is easily achievable.

FSI direct petrol injection, which cut its teeth in the V8-powered Audi R8 Le Mans racers before filtering into four and six-cylinder Audi road cars, appears for the first time in a road-going Audi V8, helping to maximise both performance and efficiency through even more effective and accurate fuel combustion."

JeeRS

I could be wrong about the exact details of the RS4 FSI engine but as with most high revving cars, the HP difference comes from the fact that the RS4 redlines at 8250. An E46 m3 has 333hp@8000 rpms but a paltry 255lbft torque. Likewise, an S2000 has 240hp@9000rpms but an even less 153lbft. Having owned both, the M3 was definitely "torquey" enough for day to day driving whereas the S2000 was just too demanding (required constant post 7000rpm shifts). S2000 was fun but horsepower w/o torque is annoying.

The D3 A8 has torque numbers of 317lbft. So too does the RS4 albeit it is at 5500rpms vs. the A8's 3500 rpms.

with high engine speeds come stronger/lighter internals. I'm sure FSI helps as well but no one really knows how much considering torque numbers are nearly the same. however, it sounds like the two engines are vastly different simply due to the fact that the internals must live up to being pounded up to 8000+ rpms.

PaulW

Yes, so true! I was wondering where all these numbers were coming from, but when I did my supercharger studies and calcs, learned a lot about HP and how puts/second (amount of power strokes) affects HP.

The higher the rev of the engine, the more puts per second, thus higher HP numbers.

But as Jee mentions, the torque of all these cars stays about the same, and that's what gets you off the line.

JeeRS

on a performance level standpoint... there's plenty of high revving cars out there. sure, you get a lighter/bolder body, rs4 trim, new rear biased quattro and of course, the FSI engine but I like cars that have good horsepower and torque numbers.

Besides, $80K?! Ouch! I wonder how many people on the waiting list will really fork over that kind of money.

I like what Audi is doing to compete in the performance front but with $80K, i want a full aluminum shell, 480hp and near 400lb torque, and sport tuned adaptive suspension. they can keep the little carbon fiber and other pseudo make-me-look-like-i-can-go-fast bits. If it's performance I want, it's performance i will pay.

In comparison, the C5 RS6 is a much better car than the RS4. Obviously, to each his own

The A8 is still the best I've ever owned though. if ever just one car, i'd be back in one again. It shares so little with the other Audis in regards to level of comfort and performance for such a big car that it almost needs to be given another marque!

greenie

that you are RIGHT!!!

Der Kimbo

No the D3 A8 engine is basically the same as the D2 S8 with a few of the features of the new 4.2