RS4 B7 Stated Power claim of 420ps

[S2tuner]

You should know better than others that it is not that simple to explain and I sincerely hope you are not claiming that the differences in the power outputs of those RS4's is down the the varying amounts of carbon build up?

Arthur is so skeptical about dynos, and so absolute about it, that I'm expecting an answer.

[ArthurPE]

Arthur is so skeptical about dynos, and so absolute about it, that I'm expecting an answer.

post the dynos with the following:
make & mfg
operator training/experience
reason for dyno run: ie, to confirm the 'value' of mods
has the operator a vested interest? ie tuning shop, or an independant 3rd party
time/date/atm conditions for each run
specs on the cars: mileage, last tune up, mods, etc.
all dyno set-up info: ramp rates, gearing, loss/correction factors, etc.

what is the inherent accuracy of a dyno? the machine itself?
what error can arise from atm temp, tire pressure, operator preferences?
ramp time can vary results alone by 20% or more...

there are 2 factors here: accuracy and repeatability...and they are not additive, they are multiplicative...so if acc ~10% and repeatabilty ~5%
error 1.1 x 1.05 ~ 1.155 or 15.5%, not 15...this adds up exponentially...not linearly

I know for a fact that a 100kw diesel drivng a generator by direct coupling (no tranny, minimal losses) and measuring power output by measuring voltage/current into a resistive load bank (0 power factor and V/i can be measured VERY accurately, down to xx.xx precision) vary by 5%+...
no changes...stop the machine and start it, same day, hours apart...

I have similar experiences with pumps...dynos are generally +/- 10% when all parameters are factored in...on the same day, same car...they go higher when the measured motive force is changed, ie, different car or engine...as high as 15%

an engine dyno is a different story, takes many variables out of the equation, maybe +/- 2%

there is no way deposits are causing 15-20% power losses as claimed by some...

I have a couple of questions for you:
is there a TSB(s) out addressing power losses/flat >5000 rpm?
how does the RS4 generate vacuum for aux devices? manifold/exh flap actuators, etc.

[ArthurPE]

one other question:
were the tests run steady state, hold peak power 1 minute? or a sweep test?
in a sweep test inertia can cause errors of >10%+ alone...

an old trick is tapping the brakes on coast down, what this does in make the loss factor much higher...
or tossing it into neutral/depressing clutch, makes them much lower...

do you want the engine to read high (confirm the value of mods) or low (confirm the NEED for mods)...

that is why all power should be wheel, NOT estimated crank...
if someone tries to foist 'crank' numbers on you, run...all they want is the ability to manipulate the numbers...

[P_G]

You should know better than others that it is not that simple to explain and I sincerely hope you are not claiming that the differences in the power outputs of those RS4's is down the the varying amounts of carbon build up?

Arthur is so skeptical about dynos, and so absolute about it, that I'm expecting an answer.

And every right he has to be too, as am I having used dyno's up and down the country of different makes under similar conditions and providing wildly different results both on this car, my S3 and S4. Hence why I don't get upset when they differ virtually very time even using the same r/r repeatedly and don't subscribe to them being the absolute measurement that RS4's are down on power.

[ArthurPE]

And every right he has to be too, as am I having used dyno's up and down the country of different makes under differing conditions and providing wildly different results both on this car, my S3 and S4. Hence why I don't get upset when they differ virtually very time even using the same r/r repeatedly and don't subscribe to them being the absolute measurement that RS4's are down on power.

please stop being reasonable & logical

will one of you millionaires ante up:
pull 20-30 engines
record all parmeters: cleaned/not, mileage, history, etc.
and engine dyno them, 3 runs each, stabilize at 7800 for 1 minute/run
then clean the uncleaned and repeat...

my guess-timate, ~$100k to $150k to perform this...
easily recoverable in a class action suit....

that is the only way, imhO, this will yeild any reliable/conclusive data...

[PetrolDave]

at the engine

Who says?

How do you know that the powertrain loss figures used are accurate?

IMHO wheel dynos are only useful for comparing multiple cars together, or the effect on changes to a single car - and then only as a means of measuring the differences and not absolute values.

For absolute values 3k-8k runs, or an engine out and fitted to an engine dyno is the the way to go.

Just my 2d...

BTW ArthurPE has a load of experience in engine development, insulting him isn't making anyone look clever, just silly.

[ArthurPE]

at the engine

Who says?

How do you know that the powertrain loss figures used are accurate?

IMHO wheel dynos are only useful for comparing multiple cars together, or the effect on changes to a single car - and then only as a means of measuring the differences and not absolute values.

For absolute values 3k-8k runs, or an engine out and fitted to an engine dyno is the the way to go.
Just my 2d...

BTW ArthurPE has a load of experience in engine development, insulting him isn't making anyone look clever, just silly.

the point is not lost on some

takes all the 'guesswork' out, and the error will generally offset...

an engine dyno is best, but not practical...
although Audi did rate the engine with one, per strict government mandated methods using an independant 3rd party...yet we don't believe them and choose to use wheel dyno figures computed off of unknown factors performed by unknown quantities...not to mention sweep vs steady state testing...it boggles the mind...like there is some sort of 'conspiracy', lol, why do people tend to believe the worst?

I'm not saying I'm 'right', just that those who claim under-rating based on these parameters, or 15% loss due to deposits, or combination there of, are 'wrong'...

I present my logic/reasoning that lead me to that conclusion, the 'other side' does the same, the reader will arbitrate the value of the arguements...and hopefully, if they can't reach a conclusion, at the very least they WILL be better informed...

isn't that what this 'forum' is all about?

[S2tuner]

Arthur is so skeptical about dynos, and so absolute about it, that I'm expecting an answer.

post the dynos with the following:
make & mfg
operator training/experience
reason for dyno run: ie, to confirm the 'value' of mods
has the operator a vested interest? ie tuning shop, or an independant 3rd party
time/date/atm conditions for each run
specs on the cars: mileage, last tune up, mods, etc.
all dyno set-up info: ramp rates, gearing, loss/correction factors, etc.

what is the inherent accuracy of a dyno? the machine itself?
what error can arise from atm temp, tire pressure, operator preferences?
ramp time can vary results alone by 20% or more...

there are 2 factors here: accuracy and repeatability...and they are not additive, they are multiplicative...so if acc ~10% and repeatabilty ~5%
error 1.1 x 1.05 ~ 1.155 or 15.5%, not 15...this adds up exponentially...not linearly

I know for a fact that a 100kw diesel drivng a generator by direct coupling (no tranny, minimal losses) and measuring power output by measuring voltage/current into a resistive load bank (0 power factor and V/i can be measured VERY accurately, down to xx.xx precision) vary by 5%+...
no changes...stop the machine and start it, same day, hours apart...

I have similar experiences with pumps...dynos are generally +/- 10% when all parameters are factored in...on the same day, same car...they go higher when the measured motive force is changed, ie, different car or engine...as high as 15%

an engine dyno is a different story, takes many variables out of the equation, maybe +/- 2%

there is no way deposits are causing 15-20% power losses as claimed by some...

I have a couple of questions for you:
is there a TSB(s) out addressing power losses/flat >5000 rpm?
how does the RS4 generate vacuum for aux devices? manifold/exh flap actuators, etc.

I don't have the sheets on my laptop, as seriously, it doesn't change anything to my life, what BHP those cars produced, tuned or not. I'm only stating facts, not trying to be the devil's advocate here.

The cars were all dynoed on our Cartec 4WD dyno in France, 2 got tuned, 2 didn't. The 350 PS one had really badly clogged intake ports and got up to 380 after intake ports and manifold cleanup, after tuning it, it produced 404 PS, but it also had decatted downpipes and an X pipe fitted to it.

Runs were done in sweep braked mode, lasted on average 20 seconds, so reasonable amounts of brake was used, and were an average of 4 to 5 runs after drivetrain losses had become stable, because if you take the first measurement only, drivetrain losses are artificially higher because of lower gearbox oil/tyre temperatures. We dyno each and every car we tune or not the same way. Intake temperatures were also similar for all the runs. The dyno is a tool for us to tune with, not a way of blowing up customers a$$es just to flatter them with good numbers.

The 380 PS car we did gained 16 PS from tuning, decent and reasonable enough for a totally stock NA engine IMO and IME. Knock control wasn't disabled, the car ran 3 to 4 degrees timing over stock, slightly leaner mixture and also a few variable cam mods done in the ECUs.

Dyno operator was the shop owner, who works with me for tuning, but has no interest whatsoever in producing artificially low or high numbers, as customers usually go to different dynos to verify our numbers anyway.

The accuracy of the dyno is simply such that each and every stock B5 S4 we put on it produces on average 267 to 275 PS at the crank if it's in a decent state of tune (recent MAF, no boost leaks, new DVs and fuel filter and stock ECU, as well as 98 RON fuel). You can call the dyno as inaccurate as you want, but as long as a stock B5 S4 produces those same numbers on the dyno, I call it as accurate as it gets. FWIW a B5 S4 is factory rated at 265 PS DIN at the crankshaft. Same example with a B5 RS4: factory rated at 380 PS DIN, each and every single stock one we've had on our dyno was never below 375 or above 388 for the best one. Whichever way you're looking at drivetrain losses, they are a part of how the Cartec dyno works (same goes for MAHA dynos used by MTM and Audi themselves), and we always look at the losses numbers in order to make sure they're stable between runs and don't artificially inflate/deflate the crankshaft figures put out by the dyno. FIY, Cartec GmbH is owned by Snap-On Inc, and the BMW factory owns about 10 chassis Cartec dynos such as the one we use. Audi have MAHA chassis dynos.

The point that I'm trying to make is that every B7 RS4 and V8 R8 out there puts down lower numbers than what the factory rates them at, whereas the V10 R8 puts down exactly what it should. Doesn't that indicate to you that there might be an issue with the design of the engine itself from the start? I'm not saying it's a <beep> engine or a <beep> car, all I'm saying is that the V10 NA FSI 5.2liter engine in the R8 simply does what it says on the tin, whereas the 4.2 V8 doesn't. Let's not even get into TFSI Golfs or RS6s, they all do within 10 PS of what the factory says they do.

I can also get you dozens of examples of B7 RS4s dynoed at Surrey Rolling Road, who is totally independent and NOT affiliated with ANY tuner in the country, and who only uses his dyno setup to measure whatever people bring to him. The best B7 RS4 he's had on his Dyno Dynamics was 391 BHP at the crank, also Sportec in switzerland, who have a very nice dyno/cooling setup have showed me similar readings, varying from 350ish for the worst to 404 for the best stock B7 RS4.

I know you keep saying there's nothing wrong with these cars Arthur, and I'm not saying they're bad cars, all I'm saying is that most seem to produce less than what they're rated at, and I'm not the only one who has "noticed" this... that's all. When a customer comes with a B7 RS4 to get tuned, what do I care if it's 350, 380 or 420 PS, as long as I know I can't gain more than 16 PS reliably on them if they're completely stock? It's not as if I dynoed a car at 350 PS stock, then tuned it and claimed 420 or worse even, 440 or 460 like some people do out there, if you catch my drift...

PetrolDave: I never meant to insult ArthurPE in any way, just tried to make him open his mind, which he doesn't seem very inclined towards, that's all.

[ArthurPE]

and you want me to 'open it' with absolutely no proof?
give me data, not heresay...convince me

[S2tuner]

Arthur, you don't get my point, open your mind, I could post each and every dyno sheet for those cars here if I could be bothered and if I had the time to waste looking them up, exporting them, hosting them and posting them, all I'm saying look at the difference between rated/measured power between V8 and V10. Had the V10 FSI engine put out say 450 PS, I'd have said it, but unfortunately, with only a Supersprint exhaust, it put down 535 crank on our dyno, a week before that it had put down 548 on Supersprint's dyno. Even without the proof, do you think I'd waste my time posting here only to be contradictory with you?

[ArthurPE]

it is moot without the set-up data...
what were the wheel HP uncorrected, raw data
post the curves

you keep saying 'open my mind', and you don't even know me...trust me, when I think someone has something to teach me, I'm in the front row...how many 50 year olds do you know who take grad engineering courses for 'fun'?

I'm going to put together a little background info on me, and the quality of my 'personal computer', then you judge...until then, YOU keep an open mind...not only about lost power due to mis-rating/deposits, but about ME...you must think I'm an idiot...

[S2tuner]

Arthur, I'm far from thinking you're an idiot, heck, I'm 20 years younger than you, I'm no one to think that, especially since I don't know you in person, and I never make opinions on anyone without having met them in person

[mark758]

Obviously much technical knowledge and experience flying around here but just to make a small very non-technical point
because one model of car consistently makes expected power on a testing machine and another model consistently doesn't I think it's a bit of a leap to conclude that the power difference is proven.

I've seen several specific different brands/models of cars never make their quoted power on a dyno but always deliver on the road.
Sometimes it's been software issues, drivetrain, cooling...

Dynos are very valuable tools and have their place for tuning development but at the end of the day cannot accurately replace road conditions.
I can say that with some confidence as I am pretty sure when I get the car out of the garage the engine power doesn't actually gain/lose 50bhp on a weekly basis but that is what dyno runs have told me it does.

As many of us have posted if our cars are underpowered there a lots of BMW V8's and Porsche units that are too or maybe not....

[^Qwerty^]

This makes interesting reading, although I'm not clever enough to understand it all:
http://en.wikipedia.org/wiki/Cylinder_head_porting

And apols if it it's been posted before.

[ArthurPE]

This makes interesting reading, although I'm not clever enough to understand it all:
http://en.wikipedia.org/wiki/Cylinder_head_porting

And apols if it it's been posted before.

the RS4 is already highly refined/developed...long runners, 4 valve/4 cam, good matching of ports, good machining/casting...and the actual air velocity is pretty low...as you would want since press drop increases as the SQUARE of the velocity...

very interesting: excerpt from the article...

The "Porting and Polishing" myth
It is popularly held that enlarging the ports to the maximum possible size and applying a mirror finish is what porting is. However that is not so. Some ports may be enlarged to their maximum possible size (in keeping with the highest level of aerodynamic efficiency) but those engines are highly developed very high speed units where the actual size of the ports has become a restriction. Larger ports flow more fuel/air at higher RPM's but sacrifice torque at lower RPM's due to lower fuel/air velocity. A mirror finish of the port does not provide the increase that intuition would suggest. In fact, within intake systems, the surface is usually deliberately textured to a degree of uniform roughness to encourage fuel deposited on the port walls to evaporate quickly. A rough surface on selected areas of the port may also alter flow by energizing the boundary layer, which can alter the flow path noticeably, possibly increasing flow. This is similar to what the dimples on a golf ball do. Flow bench testing shows that the difference between a mirror finished intake port and a rough textured port is typically less than 1%. The difference between a smooth to the touch port and an optically mirrored surface is not measurable by ordinary means. Exhaust ports may be smooth finished because of the dry gas flow and in the interest of minimizing exhaust by-product build-up. A 300 - 400 Grit finish followed by a light buff is generally accepted to be representative of a near optimal finish for exhaust gas ports.

The reason that polished ports are not advantageous from a flow standpoint is that at the interface between the metal wall and the air, the air speed is ZERO (see boundary layer and laminar flow). This is due to the wetting action of the air and indeed all fluids. The first layer of molecules adheres to the wall and does not move significantly. The rest of the flow field must shear past which develops a velocity profile (or gradient) across the duct. In order for surface roughness to impact flow appreciably, the high spots must be high enough to protrude into the faster moving air toward the center. Only a very rough surface does this.


now what this would imply is bigger isn't always better, so a small reduction in area (deposits) will not have as big as impact as you might expect...