RobC

RS7 isn't in the ETKA yet.

Here are PDFs of the RS6 charge coolers and radiators. It's not obvious from the illustrations or descriptions what the radiators are cooling as some are labeled simply as "additional radiator".

RS6 Charge Cooler
RS6 Radiators

///M Traitor

Looks like two liquid intercoolers are used instead of just one center mounted unit as on the S6. I find it interesting that the charge-air cooler appears the same though. I wonder if future "stage II" kits for the S6 will attempt to adapt the RS version intercoolers....

sciblades

heat is our cars biggest enemy my car running in 100* weather is "slow" compared to it running in 60* weather about .3-.5 seconds faster in the colder and apr proved this because their drag times were done in *45 degree weather and not even a tuned s6 by them has been able to get close to them, mainly because of the outside temperature I am sure in when the weather starts to get colder we will see new record drag times set by s6's since we are supposed to be "so" much lighter

I really need to see what stage II feels like before I shoot up to stage II+/stage III if I had not just bought wheels for the car I would be jumping all over this upgrade as my Ecu revision is only rev 002 and makes tuning a breeze.

with all that said I did ask mike last week if he will do it (tuning for bigger turbos so just waiting to see what he says)

///M Traitor

Isn't this always true and more so on FI cars? I have always noticed a stronger pull on cooler nights in every car I have owned.....

AndreyATC

Shouldnt stock car adjust boost to compensate temp difference?
I know BMW is doing this so it preserves HP at the same level, no matter what altitude or temperature it is

///M Traitor

They use altitude and temperature measurements to precisely inject the correct amount of fuel for those conditions. Fuel efficiency and emissions are the concern - not preserving HP.

I may be wrong, but I don't think a car can accurately calculate it's own HP output. It can estimate it, but not directly measure it. Plus, adding boost as ambient temperatures rise would be a dangerous combination. Usually timing and boost is pulled as intake air temps rise to prevent preignition.

The bottom line is that cold dry air is more dense and therefore has more oxygen in it. That's why cars make more power with cold dry air - because more fuel can be burned in those conditions.

I may be wrong, but that is my understanding.

DeerHunter

Turbos with electronic boost control can compensate for environmental factors, but only to a certain point. Most turbos are sized for each application to achieve a balance between good response and the desired power level. There is no free lunch, so if you want more power, you tend to give up low-end torque in exchange. That's why Audi has one set of turbos for the S6/7 and another for the S8 (and, it sounds like, yet another for the RS6/7).

Each turbo has an associated efficiency range and going outside of this range tends to produce more heat (into the intake charge) instead of more power. In other words, beyond the parameters of each particular setup, no more boost is possible (or desired).

OEMs will usually incorporate a degree of altitude compensation, where the turbos will be allowed to spin faster to cram more air into the engine as altitude increases. This restores some, but not all of the power lost to the thinner air, since the turbos are working harder and adding heat to the intake charge. Hot air takes up more space (meaning there's fewer air molecules to go bang with the fuel, so power falls) and lowers the knock threshold (which retards timing, increases Exhaust Gas Temps and reduces power). As such, a turbo car will almost always produce its maximum rated power at sea level. It will, however, lose power at a much lower rate than a normally-aspirated (or even supercharged) car.

This heating of the intake charge by working the turbos harder is the main reason why I don't know of any OEM incorporating temperature compensation to their boost control logic. It would result in "chasing one's tail" very quickly, where high ambient temps begat more boost, which raises intake temps, which results in more boost, which raises intake temps even further, and so on. It's just not a very good idea.

AndreyATC

Agreed to some.
If boost is increased at higher temp or altitude it may still be well within turbocharger efficiency parameters.
I'm not talking about doubling it, but just a small compensation, enough to pump a bit more air and extract a few ponies.
I'm not sure i got your "chasing own tail" correctly..
To me it sounded like if your car has a ECU tune, it would create a problem in hot weather or on higher altitude?
I apologize in advance if i misinterpret your explanation

P.S. Even after boost compensation, ECU will still keep it within max parameter.
For my former 335i it was 8psi for sea level, and max was 11
People with tunes are running 14psi+

DeerHunter

There is always some headroom in a well-designed turbo system, that is true. For reasons I already mentioned, OEMs generally size the turbo to the application, so this headroom is limited. This headroom is, as you say, to deal with reasonable environmental variables like altitude. At a certain point though, more boost will not result in more power because the turbo falls off the "efficiency island".

Any turbo that is well-sized for an 8 psi application (and, while I cannot guarantee that BMW didn't spec a turbo too big for that application, I suspect they probably didn't - bigger turbos are more expensive and comparatively lazy on the bottom-end) isn't running in its efficiency island at 14 psi, particularly at redline. Tuners, who love to advertise big numbers, probably program peak boost in the mid-range (which gives a nice torque bump) and then ramp it down towards redline so that it doesn't run out of flow (again, the efficiency island). Also remember that boost gauges are referenced to ambient pressure, so they will read a higher number at altitude, even though the "pressure ratio" is the same. In other words, take the psi number with a grain of salt.

Altitude compensation: This is real. OEMs will specify a maximum pressure ratio for a turbo. Modern cars have what is essentially an altimeter that will report the ambient pressure to the ECU. The MAP (manifold pressure) sensor reports the reading on the intake side and from these two, it derived the pressure ratio. Therefore, above a certain altitude, the ECU will no longer increase boost to compensate.

Temperature compensation: The intake temperature is measured on all modern cars, as it has a direct bearing on the timing map being used. Lower temps will allow more timing advance (to a point) and thus more torque and power. Of course, the opposite is true as well. On a normally-aspirated car, the relationship is fairly simple - lower temps = more air = more fuel/more timing = more power. For a turbo car, higher temps are more dangerous because the engine is already running at a higher effective compression ratio and is therefore more susceptible to knock. Spinning the turbos harder heats the air more (even if it's within the efficiency island), which likely will require timing to be dialed back, which lowers power despite the increase in boost pressure. Reduced timing also increases exhaust gas temps and will decrease the life of the cats, a big consideration for a manufacturer, since emissions components generally carry a longer, government-mandated warranty.

So why would temp-based boost compensation result in "chasing one's own tail"?: Think about it. If increasing boost increases the intake temperature, and an increase in intake temps causes a boost increase, the negative feedback loop will eventually shut things down or destroy the engine. It may be that it can be done in moderation, but I would still think it's ill-advised and have never heard of it being done before your post.

sciblades

did we ever figure out what the rs7 turbo part #'s were?