B7 RS4 Rolling Road Day 18th April 2009 (Free of Charge)

[scaghead]

nice pics jimbo it was a good day.. i cant see your gleaming monster there..

[ArthurPE]

does anyone doubt that the M3 makes 414?
the RS4 has a higher Cr (12.5 vs 12), more displacement (4.16 vs 4), the 2 variables in the torque equation T = P x D/4Pi...
it also has the advantage of DI...the M3 revs higher so that's how it over comes the P and D disadvantage, P = T x rpm
therefore ~same power...

both engines are of similar efficiency, but from what I can gather the RS4 actually may be slightly higher if mpg is any indicator...

[scaghead]

have not heard anything to say otherwise yet ArthurPE, funny i had a run with a new m3 a few weeks ago 3 runs from around 50 to 140 and they were like for like each time neither pulled away,that aint bad for a motor that is only giving me 310 shergars..

[ArthurPE]

great pics...looks like a great time...makes me green with envy

my pet peeve about the numbers? the guys with the low ones start 'worrying' about whether there is something 'wrong' with their car...this imo detracts from the enjoyment...

when in reality, you'ld be hard pressed to measure a difference on the road, if there is one!

[ArthurPE]

have not heard anything to say otherwise yet ArthurPE, funny i had a run with a new m3 a few weeks ago 3 runs from around 50 to 140 and they were like for like each time neither pulled away,that aint bad for a motor that is only giving me 310 shergars..

assuming the M3 was 'on it', this tells me your car is making more than 310 crank, especially considering you're a good bit heavier (the car, not you )

the car is acknowledged to be a good bit faster (straightline, basically 103 vs 108 or so, 1 sec+ to 100 mph) than an e46 M3 (I have one, and it is )...which tells me the wt/power ratio has to be higher...

the M3 ~10.2 lb/HP, assuming that the RS4 is only a bit better, 5% (since it's a good bit faster), say 9.7 for 4000 lbs, that's 410 HP...

[scaghead]

ArthurPE, i had a e46 before my rs and the rs is much quicker...the m3 was definetly on it [he instigated it driving right up my arse] and after two runs i pulled over to the inside lane he drove up next to me and by the expression on his face was saying nothing in it. then i pulled behind him and when we had aclear road hit it again he even pulled over at a ton because i was glued to his arse and with the toe i was having just started to creep alongside him.. so who knows what happened to mine on the rr, but driving it defo feels more there than 310bhp...maybe the fact it went on 5 mins after arriving did not help, but i cant see that making that much difference..bearing in mind i had it on a rr 3 months previous after a re- map[before 370,after 403] they hooked Vagcom up on it yesterday and showed no faults.cheers jas

[SR71]

I can certainly make investigations about "VMAX" events....we used to hire out RAF Woodbridge to race the bikes. In fact over at 200mph.org, this weekend they were hosting Judgement Day 15 there. I did the first 3 back in 2003/4.

The problem would be, whereas my 12R would max out long before the timing zone, the RS4 wouldn't, so back calculating power from VMAX knowing the aeros wouldn't work in this case as the car would still be accelerating.

I caclulated on my 12R at ~200mph you needed 3hp for every extra 1 mph which is why my bike never made it past 197mph. I just couldn't find the extra 9hp without going into the motor which I wasn't willing to do:

http://www.200mph.net/smf/index.php?topic=2370.0

Still a fun day out.

On the basis that the car will reach a GPS verified 187 mph (http://www.youtube.com/watch?v=VH7obaj5Ekw), this works out at about ~250KW (~335hp) at the wheels (density corrected to 5C, Cd*A = 0.67), which translates to a ~18% loss for a quoted 307KW car. Don't know about anyone else, but I've never seen/heard of a B7 RS4 making 335 at the wheels in the UK? What are we doing wrong over here then?

Does anyone know Craig who runs the VMAX days? I think he is probably the chap to approach initially...

No one is disputing a track day would be fun but it has no real function in ascertaining the power the cars are developing.

As for dynos, people can huff and puff about the inaccuracies of dynos using quasi-scientific approximations etc etc but if other 4WD cars are making the correct numbers (S3, S5, 996TT, 997TT) as "printed on the tin", inspite of the "correction factors", then what is the excuse for the RS4 not doing so?

This is a poor argument advanced by owners who are disappointed with their numbers!

I'd agree with you Dom81, a 5% spread I might expect, but surely you're making the data fit your conclusion rather than the conclusion fit the data!

I'm not really sure what the car's are producing, but what I'm trying to do is, in my own mind, try and explain why the experiments produce the figures they do!

If a car produces the power on the road but not on the dyno, why?

If one car produces alot more power on the dyno compared to another, but on the road, performs the same, why?

I'm sure the clever transmission has something to do with it but then everything suggests that the transfer functions for the electronics controlling the diffs must have time constants much smaller than the ramp rates on the dynos...

I agree with ArthurPE, in that the numbers seem to add up on the street, but why then the discrepancy on the dyno, and even more curious, why the spread in results between the "same" cars?

Still, all good fun.

[scaghead]

I can certainly make investigations about "VMAX" events....we used to hire out RAF Woodbridge to race the bikes. In fact over at 200mph.org, this weekend they were hosting Judgement Day 15 there. I did the first 3 back in 2003/4.

The problem would be, whereas my 12R would max out long before the timing zone, the RS4 wouldn't, so back calculating power from VMAX knowing the aeros wouldn't work in this case as the car would still be accelerating.

I caclulated on my 12R at ~200mph you needed 3hp for every extra 1 mph which is why my bike never made it past 197mph. I just couldn't find the extra 9hp without going into the motor which I wasn't willing to do:

http://www.200mph.net/smf/index.php?topic=2370.0

Still a fun day out.

On the basis that the car will reach a GPS verified 187 mph (http://www.youtube.com/watch?v=VH7obaj5Ekw), this works out at about ~250KW (~335hp) at the wheels (density corrected to 5C, Cd*A = 0.67), which translates to a ~18% loss for a quoted 307KW car. Don't know about anyone else, but I've never seen/heard of a B7 RS4 making 335 at the wheels in the UK? What are we doing wrong over here then?

Does anyone know Craig who runs the VMAX days? I think he is probably the chap to approach initially...

No one is disputing a track day would be fun but it has no real function in ascertaining the power the cars are developing.

As for dynos, people can huff and puff about the inaccuracies of dynos using quasi-scientific approximations etc etc but if other 4WD cars are making the correct numbers (S3, S5, 996TT, 997TT) as "printed on the tin", inspite of the "correction factors", then what is the excuse for the RS4 not doing so?

This is a poor argument advanced by owners who are disappointed with their numbers!

I'd agree with you Dom81, a 5% spread I might expect, but surely you're making the data fit your conclusion rather than the conclusion fit the data!

I'm not really sure what the car's are producing, but what I'm trying to do is, in my own mind, try and explain why the experiments produce the figures they do!

If a car produces the power on the road but not on the dyno, why?

If one car produces alot more power on the dyno compared to another, but on the road, performs the same, why?

I'm sure the clever transmission has something to do with it but then everything suggests that the transfer functions for the electronics controlling the diffs must have time constants much smaller than the ramp rates on the dynos...

I agree with ArthurPE, in that the numbers seem to add up on the street, but why then the discrepancy on the dyno, and even more curious, why the spread in results between the "same" cars?

Still, all good fun.

i think you have hit the nail on the head could not agree more

[rAudiguy]

especially considering you're a good bit heavier

You've met him then??

[reevesroadster]

Just to add to the above posts, the vehicle above quoted at 187mph verified GPS had been remapped. I had the opportunity of a few runs with the owner (mines an Avant, and this one is a saloon) and we even swapped cars to compare performance - mines stock. There wasnt much difference between the 2 cars, although we only ran to about 130mph on our private road. The saloon was slightly faster, but the major difference in the cars was that the saloon car was alot smoother and benefited from better response through the lower rev range (as would be expected from a remap).

[ArthurPE]

SR71, good post...
the electronics may be interferring, maybe sensing slip or something...
was timing observed during the runs? fuel rate?
iirc these dyno's measure torque by the rate of accel, so you can't do a steady state power measurement, say 7500, 4th gear for 15 seconds...

but we don't know what these cars made at the wheels...only what they supposedly made at the crank, with unknown correction factors...

can someone please post some dyno charts, raw data, uncorrected, at the wheels...torque preferably...

excluding the 2 tuned cars, and the top and bottom 5, the average is 358 HP...
if a 10% correction factor was used then wheel ~322 or so...
if 20% (which I believe is close to actual at peak) then 285 at the wheels...no way...

the problem with correction factors...they are not the same at all rpm's, they vary with speed, for example they are ~ 13% at torque peak of 5550 and 17% at HP peak of 7550, per rototest numbers...
http://www.rri.se/popup/performancegrap ... artsID=281

as would be expected since losses are ~linear
7550/5550 x 13% ~ 17.5%

[ArthurPE]

which dyno was used? http://www.dyno.com.au/dyno/controller/specs
the awd 450ds or awd 450ds qr?
the qr has load retardation on each wheel, I assume the base only on the rear...

interesting:

Interesting Dyno Factoids (Dyno Dynamics, Mustang, Dynojet)

--------------------------------------------------------------------------------

20) My car makes 300 hp but your dyno says it makes 215. What is up? Our dyno is the most accurate measurement of torque at the wheels. More accurate than most. No "interpolation" or "estimation" or "inertia factors" are applied like they are on other competitors' lesser machines. What this means is that this is the actual torque being applied at the tire. Typically, a 300hp all wheel drive car will measure in around 210-215 on our dyno. This is normal.

21) I went to a Mustang dyno and they said theirs reads low, but you say yours reads low. Is this just some trick used by tuners? The Dyno Dynamics is known throughout the industry as being the "heartbreaker" dyno - because it breaks the heart of every man that thinks he has 500 hp when he really has 350. The Dyno Dynamics reads lower than the Mustang. It reads WAY lower than a Dynojet. It reads WAY lower than a Dynapack (which actually reads too high on tip-in). The closest in numbers (at low HP) is the mustang, but using the above example, the same 300hp car was dyno'd back to back on a Dyno Dynamics 450 LowBoy (what we have) and a Mustang AWD500E (what some other guys have), and that 300hp rated car consistently read 223 on the Dyno Dynam ics and 249 on the Mustang. One hour apart, exact same car, same town, same altitude, etc.

[Gazzer68]

I think it's all in the cars electronics?
Dyno confuses it !
Do's the EPC really switch off?
Was it switched off on Saturday?

[SR71]

I think the data is coming Arthur...

In http://www.pumaracing.co.uk/POWER3.htm you can find the claim that

Finally, the biggest source of loss in the entire transmission system of a car is in the tyres - they account for half or more of the total losses between the flywheel and the rollers. Each set of driven gears, i.e. the final drive gear or the particular gearbox ratio that you happen to be testing the car in, only absorbs about 1% to 2% of the engine's power.

I wonder if there is a correlation there?

The guys at the lower end of the spectrum will all be out measuring their tyre pressures tomorrow!

But if nominal losses are ~20%, if the above statement is true, you could find the figures varying ~40hp purely on account of your tyre pressures!

Morale of the story: 50psi for the dyno!

[ArthurPE]

SR71, thanks good info:

excerpts:
The moral of the story is clear - if you don't know the power at the wheels you don't know diddly-squat - so as the man in Hill St Blues used to say - "be careful out there folks".

4wd cars will have higher losses because of the extra differentials and other power transmission components. The tyre and main gearbox losses will be the same though. Correlating the performance of vehicles with the both 4wd and 2wd options (Audi's and the Sierra Cosworth are examples) shows 4wd transmission losses to be about 5% higher than rwd. 22% seems to be a good average.

There is enormous pressure on rolling road operators to be able to quote flywheel bhp rather than wheel bhp and most operators now run proprietary software systems which "supposedly" print out flywheel power.
PROBLEM !! - THESE SOFTWARE SYSTEMS DO NOT AND CANNOT WORK !!
Yes - I know - the whole chassis dyno tuning industry quotes flywheel figures and here's me saying none of it works. So I'd better explain some more and then you can make your own mind up.

Chassis dynos are essentially for tuning purposes, they are not well suited to giving an accurate hp figure.

Chassis dynos are essentially tuning aids, not true hp measurement devices. Use them to dial in your EMS mapping, not to brag to your friend's that you made XXX hp.