S4 4.2 vs RS4 4.2

[DeatschWerks]

What is the difference between the two? I have a feeling it is mainly in the head... am I right?

[bklein8888]

340HP S4 4.2 V8 + FSI = 420HP RS4 engine
Supposedly they're not related other than the block itself, though when you drive one after the other, it seems hard to justify the $20k price difference. I know many will disagree (and I have started a thread that argues this point in more detail)

sorry if this was considered a thread jack but in short, the engines are very different

[DeatschWerks]

A quick search of Car and Driver showed me they are very different indeed...

"A derivation of Audi's corporate 4.2-liter V-8, the engine boasts new pistons, connecting rods, and cylinder heads; a new crankshaft"

Plus it looks like the new M3 V8 is one-upping the RS4 =(

[Kappe]

for starts a different engine. The RS4 gots a high reving 420HP FSI 4.2, max 8250RPM and has like you see above new pistons etc. The S4 has the normal 7000RPM 4.2 344HP "low" reving engine.

The second thing is that they have used alluminium body panels in the front to try to decrese the understeer that all the older audis got.

third is the quattro drive train. In the RS4 the torque can shift for 85% to the back wheels. In combination with the alluminium front body panels it lifts a lot of understeer and makes it a more nutral ride in corners.

The RS4 has an 18-inch brake system that ensuring optimum stopping power. It has cross-drilled, inner-vented brake discs at the front measure 365 millimetres in diameter, as opposed to 324-millimetre brake discs at the rear. Flow-optimised ventilation geometry incorporating Naca jets on the underfloor of the car ensures first-class cooling of the brakes under all conditions.
As a result, brake fading is significantly reduced even under extreme loads, for example on the race track.

And in this case quattro drive is further enhanced by Audi's DRC Dynamic Ride Control, significantly reducing both body roll and dive.


all with all. The S4 just is a harder and bigger engined A4. The RS4 just is a whole new experience

[ieatfishburitos]

He wants details on the engine differences, not the cars..

[Chris from Cali]

The S4 just is a harder and bigger engined A4. The RS4 just is a whole new experience

This is very true. I owned a B7 S4 and the RS4 is light years beyond it... And it's not a $20K difference - more like $11-12K.

He wants details on the engine differences, not the cars..

I didn't read it that way - sounds like he's asking about the cars.

[DeatschWerks]

Now that I re-read it, it does look vauge, but really I was inquiring about the engine differences.

I love my new S4 but I'm already having dreams of trading it for an RS4 in a couple years =)... and this really isn't a dig at the S4, rather I love it so much I wouldn't mind paying paying even more for an even better version (don't let my wife see this - LOL)

What about compression ratios?

[V-8]

What is the difference between the two? I have a feeling it is mainly in the head... am I right?

Here's an older thread with a little info on this topic:

http://www.audizine.com/forum/showthread.php?t=101550

Photos showing the header differences.

S4 header:



Improved RS4 header:



Just for comparison, further improved R8 header:



Here's a good read with detailed differences between the high-revving 4.2L FSI engine and the standard 4.2L FSI:

http://forums.audiworld.com/rs4b7/msgs/52116.phtml

[V-8]

third is the quattro drive train. In the RS4 the torque can shift for 85% to the back wheels. In combination with the alluminium front body panels it lifts a lot of understeer and makes it a more nutral ride in corners.

Just to clear things up a bit here, as of 2006+ the S4 and RS4 use the same Quattro system with 40:60 split. I've also read that 2006+ S4's also have the same 22mm rear sway bar that the RS4 uses.

[Kappe]

Just to clear things up a bit here, as of 2006+ the S4 and RS4 use the same Quattro system with 40:60 split. I've also read that 2006+ S4's also have the same 22mm rear sway bar that the RS4 uses.

thats true. But not the maximum 85% to the rear

[supradriver094]

Looking at the comparision pictures of the headers, would the RS4 headers fit on an S4? I know that many of the B5 owner use RS4 parts to mod their S4s, so I was just wondering if any of the parts can be used on the S4. If not the headers maybe something else?

[DeatschWerks]

The flow on the stock S4 header does not look good at all... basically a log manifold. If someone made a 4-1 or a 4-2-1 header, I bet it would make quite a bit of power.

[V-8]

Looking at the comparision pictures of the headers, would the RS4 headers fit on an S4? I know that many of the B5 owner use RS4 parts to mod their S4s, so I was just wondering if any of the parts can be used on the S4. If not the headers maybe something else?

I don't think the RS4 headers will fit on the S4, it's highly unlikely.

[ieatfishburitos]

Yes that stock s4 header or should I say manifold looks horrible. Cmon aftermarket people, lets get a better design that gives us 20hp.. :) In the V8 NA world, the headers are a fairly standard upgrade..

[M power this!]

Actually the current S4 sticks that have the 40/60% biased like the RS4 will indeed go upto 85% rear. it's a mechanical system that sends power forward or rearward due to torque demand. a normal 50/50 car in stick will send 75% front or rear. by changing the biased, you're changing the limits as well. also, the 85% rearward max cars can now only send 65% to the front.

on the engine, they're much much different. there's a good amount of titanium used in the RS4, a much harder cylinder wall (why they use so much oil in the beginning) and actually have the highest piston speed of ANY production V8. of course higher than the Ferraris that do have a higher revlimit.

[Chris from Cali]

on the engine, they're much much different. there's a good amount of titanium used in the RS4, a much harder cylinder wall (why they use so much oil in the beginning) and actually have the highest piston speed of ANY production V8. of course higher than the Ferraris that do have a higher revlimit.

Very interesting post... I have already gone through 3.5 qts in the first 3600 miles.

[i_eat_staples]

it confuses me that APR/AWE would develop an SC for this car before headers...did they try and the gains werent there for the headers? maybe the stock ones have better flow than perceived?

[Alister]

Another interesting comparison would be between the S5 engine (4.2 FSI V8 w/ 260kW) and the S4 and RS4 engines..

I assume the S5 FSI engine is just a detuned version of the RS4's engine?

[Kappe]

Actually the current S4 sticks that have the 40/60% biased like the RS4 will indeed go upto 85% rear. it's a mechanical system that sends power forward or rearward due to torque demand. a normal 50/50 car in stick will send 75% front or rear. by changing the biased, you're changing the limits as well. also, the 85% rearward max cars can now only send 65% to the front.

on the engine, they're much much different. there's a good amount of titanium used in the RS4, a much harder cylinder wall (why they use so much oil in the beginning) and actually have the highest piston speed of ANY production V8. of course higher than the Ferraris that do have a higher revlimit.

the normal 50/50 like in the A4 sends a maximum of 68% to the rear wheels. The 40/60 does 75% max on de rear and the RS4/S5 85%. The R8 always sends 85% in normal conditions to the rear.

[RAudi Driver]

The RS4 has an 18-inch brake system that ensuring optimum stopping power. It has cross-drilled, inner-vented brake discs at the front measure 365 millimetres in diameter, as opposed to 324-millimetre brake discs at the rear. Flow-optimised ventilation geometry incorporating Naca jets on the underfloor of the car ensures first-class cooling of the brakes under all conditions.

18" braking system?

[Kappe]

dunno.. Copy past that part tbh..

[probitron]

I think that means it can only fit a wheel 18"s or larger. Chris from Cali was complaining in an S5 thread that some car magazines tend to measure brake size that way, which is confusing.

[Kappe]

would be nice tho. 22" rims with 18"disks

[Chris from Cali]

I think that means it can only fit a wheel 18"s or larger. Chris from Cali was complaining in an S5 thread that some car magazines tend to measure brake size that way, which is confusing.

I think "complaining" is a bit harsh...

I was just pointing out that some measure the brakes by the size of wheel required. Like hp/bhp/PS/kW/etc., I wish there was some standardization when it comes to brake size. I think measurements in mm would make everyone happy...

[DeatschWerks]

I emailed APR about making headers for the 4.2 S4. They did agree that it would probably make good power. However, they also said they do not plan on ever releasing one due to high cost of manufacturing...

[M power this!]

68% is for Tiptronic cars (max to front or rear axle)
75% is for stick cars (max to front or rear axle)

both being 50/50% cars in normal drive

RS4 and 40/60 S4s (stick only) have same end result max of 85%

R8 is 85% under normal rear biased with the ability to get 35% to the fronts. it's a Viscous Coupling system, not Torsen

[Kem]

To me when one says detuned I think ECU and maybe airbox + exhaust. I can guarantee you there are many differences within the engine between the two. FSI is not why the RS4 makes power.

Another interesting comparison would be between the S5 engine (4.2 FSI V8 w/ 260kW) and the S4 and RS4 engines..

I assume the S5 FSI engine is just a detuned version of the RS4's engine?

[Kappe]

68% is for Tiptronic cars (max to front or rear axle)
75% is for stick cars (max to front or rear axle)

both being 50/50% cars in normal drive

RS4 and 40/60 S4s (stick only) have same end result max of 85%

R8 is 85% under normal rear biased with the ability to get 35% to the fronts. it's a Viscous Coupling system, not Torsen

where did you get the info about the A series stick and TT difference on the torsen specs? I just seen 68%, not telling me it was only on the TT..

[Shomegrown]

The engines are 99% different.

Someone posted above that the cylinder wall material is different. This is definitely false. They are both aluminum blocks with Alusil bore coatings. The difference is that the RS4 block is stress-plate honed and the S4 isn't.

Both engines are known to swill oil.

Anyway, the engines are dimensionally similar, but very few parts are shared between them.