RS4 redline = 8000 RPM.

B6/7 S4/RS4
#1

I wanted to get a discussion going about the super lofty redline of the B7 RS4, which revs out to a redline of 8000 RPMs and a rev limiter I believe at 8200 RPMs. I have talked with a few smart people about the mechanics of the high RPMs and it’s pretty incredible.

When you consider that at 6000 RPM the pistons each travel from top dead centre, down and up through the full stroke and back to top dead centre 100 times per second, that’s hard to imagine.

When you consider that at 7000 RPM ut us 117 times per second (!), it’s a level the grand majority of cars do not reach. My old B7 S4 did, and that was pretty interesting. Not many cars see more than 6000 or 6500 RPMs. In talking with a few people on the OEM side the strength and tolerances required to take a motor from 6000 RPM to 7000 RPM are MASSIVE. I guess that’s a good reason for keeping revs down. Many many technical problems have to be overcome, stronger materials, and really when you think about it, just trying to make combustion keep up with the speed everything is moving at is pretty incredible.

When you then go beyond 7000 RPM, on a production vehicle, you are now in rarified air, the task is so large. The B7 RS4 revs out to a redline of 8000 RPM, which means that piston is travelling its full range 133 times per second! When you drive one, to coin a phrase from former RS4 owner richib86, revving it out to redline it sounds like the motor is going to pop. To take a V8 to 8000 RPM is certainly a crzay thing. The 355, 360 430 and 458 V8 Ferraris all did this and beyond, and if you ever hear one, it doesn’t sound like a V8 at all…the pitch is so freakishly high. The RS4 doesn’t get near that, however at 8000 RPM it certainly sounds ‘different’.

The first time you drive an RS4, coming from say a B6/7 S4 with a normal 6800-7000 RPM redline, you first realise that you are shifting WAY too early. I used to shift around 6500 in my B7 S4 when letting it fly. You just get used to the sound/feel/timing of a motor going through the gears, and when you approach your normal shift point you find yourself shifting. I drove an RS4 for the first time a few years ago, and while racing a friend in his S4, my passenger in the RS4 with me kept making fun of me for shifting with 1500 RPMs of usable acceleration left on the table. It’s hard to let it go to 8000.

The new Audi RS4 (B8) and RS5 have an all new engine. It’s still a 4.2 FSI, and it’s still a high revving motor, but they started virtually from scratch when building it including all new internals. One of the reasons behind that was to fix a few things that they didn’t like in the B7 engine, and another reason was to accomodate an even deeper redline. The new variant is pushed all the way to 8500 RPM. An incredible 142 revs per second. I would love to know what they put into the new engine to accomodate that.

Anyway, if anyone can share a little more on the mechanics and difficulties of running a motor out to 8000 or so, please share. Also if you’ve driven any other super revving elite motors, share your experience.

#2

I don’t have much input besides bikes…I had a 2008 R1 that redlined at something ridiculous, around 14k RPMs. To be honest it just doesn’t feel right…feels like the engine is just going to explode.

I really need to test drive an RS4 because I couldn’t imagine a car with a V8 at 8k RPMs! My S4 screams at 6500-6800…and taking it another 1k RPMs would be nuts.

The requirements and technical aspect behind it is truly a remarkable thing to think about.

#3

Great post.

#4

one thing to considering regarding the ferrari V8 exhaust note is that they are a flat plane motor. the exhuast pulses on each bank come out orderly every 180* (like an I4 on each bank) vs a cross plane V8 where you get simultaneous pulses at times followed by extended gaps (more like two V4s end to end). a cross bank header design (such as a gt40) gives the collectors in a cross plane V8 exhaust flow more like a flat plane V8’s.

iirc the old audi v8 dtm cars had a flat plane motor, the story is they got around the stock component restriction by bending a stock crank back to to being flat

regarding increasing redline, a mild increase can dramtically increase stress the rod experiences, along with all essentially the motor as a whole. typically thats why you see a whole new unit designed for those kind of revs, the classic example being the Q7/S5 4.2 vs the RS4 4.2 and i’d bet the RS4 4.2 vs the new RS4/5 4.2 for that extra few hundred rpm.

a fun exercise is to calculate piston speed based on stroke and rpm, a nice way to compare say a bike/f1 motor vs the comparatively undersquare (long stroke) high rev audi motors.

even more interesting would be to determine the instantaneous acceleration as the piston passes tdc and starts to move down.

#5

It takes a massive amount of work each rpm over 7000. If you build a gm or even an audi motor and you talk to a real motor builder… not a backyard guy that just tosses motors together but a real motor builder this is a big deal. Under 7000 rpm you can use standard rod bolts at 7200+ you need completely different bolts at 7800rpm it changes again. After 8000 everything gets even more serious you need different specs on lifters guids rods valves. The gap from 7000 to 8000 is something that requires all new components the gap from 8000 to 8500 requires even more changes.

The audi q7 and the audi rs4. The difference between those two motors shows just a small window into what it takes. Your talking new heads rods timing chain timing components the list goes on.

#6

Some bikes go to 25K rpms! That was creepy as hell just maxing out first gear. I swear you would only need first to third for everything.

#7

Chris, what would be the first items to see failure in your opinion with just a bump of 500 RPMs? Do heads usually suffer first or the bottom end? It’s crazy to think about piston speed and acceleration…then on top of that the speed at which the valves will be moving and the added strain (not sure if that is the correct term) on the springs and other components.

That is freaking nuts! First gear was ridiculous with the R1 I think it would do over 100mph in first.

#8

One of my cars do 9500 rpm and trap on the vbox 146mph … I will write later about this motor , for me its a piece of gold… stock bottom end can take over 550hp and 400lbs of torque almost for ever…its a 4 cylinder car not a honda or a mitsu.
Now going out with the wife and babys.
later guys.

http://i38.photobucket.com/albums/e116/jpsr20det/sr20ve-t%20p11-jp/P1020347.jpg

#9

…fuck taptalk

#10

Heads would definitely go first. You would probably float a valve.

#11

Paper can really add soms idea as I know he said eurocode did some crazy 8500 builds and I would wager to say that thr amount of money and quality parts to extend the motor that high were a big list.

Most all the motors I build are under 7000 rpm. I cant stress enough that you cant just extend a rev limmit on any car and the higher the rev limit 7 8 or 8.5k the more dangerous it is to extend it. I know jhm reduced the rev limit on the s4 kits I think its a smart idea. I would like to see them reduce the rev limit on the rs4 kits like apr did. Extending the rev limit on a stock car is scarry at 7000 and even more at 8000. Adding a power adder you should be reducing the rev limit due to the encrease of efficency of the motor.

#12

This below is part of the list of the changes that went into getting the 7000rpm up to 8000

Different Features of the
High-revving Engine
To match the higher engine power output and RPM, the
following cylinder head components were modified:

Intake ports are charge optimized (based on larger
cross-sections)
Intake valves are chrome-plated hollow stem valves
(for weight reduction)
Valve springs are made of a material with higher
tensile strength and also have higher spring force

To meet the higher fuel requirements, the injectors are
designed for higher flow rates.
Roller rocker arms are more robustly designed, with
peened rollers for higher strength

Camshafts have different timings and larger opening
lengths

Intake valve opening angle 230 crank angle degrees

Exhaust valve opening angle 220 crank angle degrees

The lifters were adapted from the 3.2L V6 engine found
in the TT and A3. They have a larger ball stroke which,
in the course of testing, proved advantageous for the
high-revving engine (with regard to the inflation of the
hydraulic valve clearance compensation element).

The cylinder head has a modified water jacket which
circulates coolant to the area between the intake port
and the injector, thereby reducing the temperatures in
the cylinder head combustion chamber plate.

Due to a modified camshaft drive reduction ratio, the
camshaft adjuster has 25 teeth for the chain drive, as
opposed to 30 teeth in the basic engine

#13

the rods & pistons were also different alloys to better resist the extra tensile stress as rpms go up

#14

component load goes up with the square of rpm.
scary juju.
hi guys, i’m fresh here, have an 04 s4 mt.

edit for mike; post in quote

#15

S4mikey- Can you expand more on what you were saying about component load?

#16

At its release, the B7 RS4 was the only “RS” with a NA engine.

The engine was based on the existing all-alloy 4.2 V8 from the B6 S4, sharing many parts with the 4.2 FSI V8 engine in the Q7. There is a spectacular technical training manual available on the interweb that details many of the differences between the Q7 engine and the RS4 engine.

As Saki says, the redline is at 8,000 rpm, but not yet mentioned is the rev limit of 8,250 rpm.

Some additional differences from the Q7 engine, that the RS4 engine has

  • increased crankcase breathing
  • low-pressure fuel return system
  • lateral g-based oil sump baffling
  • four valves per cylinder (instead of five)
  • cast magnesium alloy fixed tract length intake manifold with adjustable tumble flaps
  • secondary oil air-liquid intercooler
  • two ‘4-into-2-into-1’ alloy steel exhaust manifolds (HOT ROD!)
  • two Bosch electronic engine control units
  • heavy metal weights added to balance crank for high speed operation

I’ll see if I can pull up the manual (its at home) to add some additional interesting highlights!

#17

Have you ever logged your car running to 8250 RPMs? I haven’t.

I think the rev limiter is around 8200 however my logs don’t seem to get there.

Also, I wouldn’t say it was ‘based on’ the B6 S4 engine anymore than it was ‘based on’ the 4.2 A6/A8 belt engine or the 4.2 twin turbo RS6 engine.

They share a number of cylinders and displacement, but the engines are entirely different. Dramatically different in fact. The block, the heads, the internals…everything is entirely different other than the nomenclature of the B6 engine.

There are similarities…I believe bore/stroke/wall thickness are the same and they are both using chains for timing components and 3 radiators, but the actual engines themselves are distant cousins more than siblings. There’s an image provided by audi showing the various 4.2 engines and you can see they are quite different to look at.

#18

its much fairer to say its based on the bhf design vs the older 4.2 design.

same fairly unique accessory drive setup
same stroke, which is not shared with the timing belt 4.2s (they are a 93.0mm stroke)
timing system
block casting and finishing processes (mechanically vs chemically stripped blocks) are more similar between the timing chain motors vs the timing belt motors

there are lots of differences but from a design standpoint it was an evolution vs the 32v to 40v or timing belt to timing chain motor design revolutions.

all of the fsi motors (including the s5/q7 4.2s) are 4 valve. obviously the valvetrain in the highrev motor were worked over in other ways

#19

Yes the book may say the rev limit is 8250 but it is hard to push it that far. I only bounced off the rev limiter once in a customer’s car and it noticeably cut the power before I could get into second, talk about safeguards.

I don’t like to say one Audi engine is based off another because they keep trying to improve things as they progress. So look at the timeline of which engines came out:
2004 4.2 MPI S4
2005 3.2 FSI in the C6 A6
2005.5/2006 2.slowT in the bastard B7 A4
2007 4.2 FSI in the high revving RS4 and Q7

So it appears to me that Audi took the rear timing chains and other technology from the 2004 S4 to make the 2005 3.2 while adding FSI. Next they designed the 4.2 FSI to expand over the model line up kind of like how the 2.7T was a high performance engine in the B5 S4 and then a hauler in the C5 A6. Don’t pay attention to the 2.slowT reference because that was a step backwards when compared to the V-engines technology-wise. Of course each engine is a little different but the concept is largely the same.

#20

Good question: I haven’t logged at all, actually. No specific engine data. When I row the gears on mine, I have no calibrated instrument keeping track of peak rpm, LOL

My reference is only from user’s manual, and the technical manual published by Audi.

Good stuff! (My bad on the valves per cylinder, not sure where I misunderstood that.)

More good stuff!

As a newb to Audis, I find all this background fascinating!