A little more insight into power, mods, etc....
07-11-2007, 05:34 PM
#1
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A little more insight into power, mods, etc....
Since the RS4's introduction, independent dyno tests of the car have varied greatly. Dyno's of Milltek equipped vehicles have varied, and the whole question of auxillary intake flap function has emerged. The bench hp claims for the engine were also called into question. This prompted me to try and seek some answers.
Now...... those of you who were into the Audi scene in the early part of the decade may remember that I was pretty well connected into the Audi tuning circuit as well as having some contacts with people in the Audi racing program. While I can't exactly call these people up and go out for a beer, they did still remember me and I was able to gather some information to share.
Firstly, please don't ask me where I got the info. I won't tell you. I can't name names and everyone should respect that.
So...here's what I discovered on the RS4 engine and the power it produces.
First is the question of whether this motor produces 420hp. Yes it does...... when the conditions are ideal. Basically, the motor produces more power by one primary mechanism:timing advance. The RS4's ECU is exquisitly sensitive to any conditions that may warrant a timing retard. Pretty common sense when you think about a car running at 8000rpm on a 12.5:1 compression.
What this translates to is that when the fuel octane is off even a little, when it's too hot or too humid out, when you are at altitude, when the oil pressure is off a little, the car will cut power production....moreso than other cars might. Any engine can make 60hp/liter under a wide variety of conditions, but a street reliable normally aspirated motor that is called upon to produce 100+hp/liter will only do so when the conditions are perfect. This phenomenon is not unique to the RS4. It is there in a Honda S2000 and it will be there in the new M3. If you want a normally aspirated motor that can produce it's claimed power under a wide variety of conditions, get a late 90's Dodge Viper. 470hp out of 8 liters. There is no replacement for displacement.
Speaking of octane, don't expect to be making 420hp on California 91 octane. 93-94 octane is a minimum to get the claimed power output. The testing and development were done with European 98 octane. Actually my sources had differing opinions on whether the car would produce maximum power on common US street fuel of 93/94 octane vs. Euro 98. In any case, under ideal conditions with 93 octane, it is safe to say the engine will produce over 400hp. In the summer, in the California high desert with 91, you may be making 360-370 hp. Remember, air temp alone will lead to a 0.4hp drop per degree farenheit increase in intake temps.
Secondly....mods. As one would guess, when conditions are ideal, meaning cool, dry, sea level air, and high ocatne fuel, the ECU will allow this baby to run....really run. In this circumstance, you will should a decent power gain from DP/catback.
Finally...the ECU itself. Sorry to say, it's going to be nearly impossible to hack/tune safely without direct input from Audi. The encryption is very high level. Piggyback computers notwithstanding. However, I wouldn't want to run a piggy back on an engine with so little room for error.
Hope this helps clear things up. When the temps start to cool off, I myself am going to go fill up on 100 octane for a tankful just to see what the butt dyno says. maybe I'll even do a dyno run.
Now...... those of you who were into the Audi scene in the early part of the decade may remember that I was pretty well connected into the Audi tuning circuit as well as having some contacts with people in the Audi racing program. While I can't exactly call these people up and go out for a beer, they did still remember me and I was able to gather some information to share.
Firstly, please don't ask me where I got the info. I won't tell you. I can't name names and everyone should respect that.
So...here's what I discovered on the RS4 engine and the power it produces.
First is the question of whether this motor produces 420hp. Yes it does...... when the conditions are ideal. Basically, the motor produces more power by one primary mechanism:timing advance. The RS4's ECU is exquisitly sensitive to any conditions that may warrant a timing retard. Pretty common sense when you think about a car running at 8000rpm on a 12.5:1 compression.
What this translates to is that when the fuel octane is off even a little, when it's too hot or too humid out, when you are at altitude, when the oil pressure is off a little, the car will cut power production....moreso than other cars might. Any engine can make 60hp/liter under a wide variety of conditions, but a street reliable normally aspirated motor that is called upon to produce 100+hp/liter will only do so when the conditions are perfect. This phenomenon is not unique to the RS4. It is there in a Honda S2000 and it will be there in the new M3. If you want a normally aspirated motor that can produce it's claimed power under a wide variety of conditions, get a late 90's Dodge Viper. 470hp out of 8 liters. There is no replacement for displacement.
Speaking of octane, don't expect to be making 420hp on California 91 octane. 93-94 octane is a minimum to get the claimed power output. The testing and development were done with European 98 octane. Actually my sources had differing opinions on whether the car would produce maximum power on common US street fuel of 93/94 octane vs. Euro 98. In any case, under ideal conditions with 93 octane, it is safe to say the engine will produce over 400hp. In the summer, in the California high desert with 91, you may be making 360-370 hp. Remember, air temp alone will lead to a 0.4hp drop per degree farenheit increase in intake temps.
Secondly....mods. As one would guess, when conditions are ideal, meaning cool, dry, sea level air, and high ocatne fuel, the ECU will allow this baby to run....really run. In this circumstance, you will should a decent power gain from DP/catback.
Finally...the ECU itself. Sorry to say, it's going to be nearly impossible to hack/tune safely without direct input from Audi. The encryption is very high level. Piggyback computers notwithstanding. However, I wouldn't want to run a piggy back on an engine with so little room for error.
Hope this helps clear things up. When the temps start to cool off, I myself am going to go fill up on 100 octane for a tankful just to see what the butt dyno says. maybe I'll even do a dyno run.
07-11-2007, 05:43 PM
#2
MTM has already been into the MED9 for RS4 and ...
hence the MTM supercharged RS4 clubsport and their software available for bumping the limiter. APR, REVO, and GIAC have all been into other of the latest MED9 computers. The question is if it is worth it. Are enough sales of chips that only gain 10 or 15hp on a limited production car going to justify the considerable RandD?
EDIT:
and information on timing for Bosch Motronic...
A twin three-dimensional table lookup that corrects the ignition timing angle for intake air temperature and is also a function of engine load, and engine speed.
PLUS
A three-dimensional lookup that corrects for engine coolant temperature and is also a function of load.
PLUS
The main timing lookup table which is a function of engine speed and engine load. On variable valve timing or variable cam lift engines this can be two or four tables that are representative of the state of the switchover. These timing lookups are the ones that are changed in performance chips. Bosch refers to these lookups as the base RON lookup tables.
PLUS
A three dimensional lookup that corrects for air-fuel ratio and is also a function of engine speed. (This lookup is not utilized on all engines, on some engines all values set to zeroes.)
PLUS
Ignition timing adaptation values.
PLUS
Cylinder selective timing retardation. (knock sensor activity)
=
Ignition advance angle
EDIT:
and information on timing for Bosch Motronic...
A twin three-dimensional table lookup that corrects the ignition timing angle for intake air temperature and is also a function of engine load, and engine speed.
PLUS
A three-dimensional lookup that corrects for engine coolant temperature and is also a function of load.
PLUS
The main timing lookup table which is a function of engine speed and engine load. On variable valve timing or variable cam lift engines this can be two or four tables that are representative of the state of the switchover. These timing lookups are the ones that are changed in performance chips. Bosch refers to these lookups as the base RON lookup tables.
PLUS
A three dimensional lookup that corrects for air-fuel ratio and is also a function of engine speed. (This lookup is not utilized on all engines, on some engines all values set to zeroes.)
PLUS
Ignition timing adaptation values.
PLUS
Cylinder selective timing retardation. (knock sensor activity)
=
Ignition advance angle
07-11-2007, 09:53 PM
#5
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Well in that case, hight octane fuel should really help out the RS4, specially in high temps!
I am not doubting you, but iirc it has been noted here that high octane fuel makes little to no difference in power gains on an RS4. I am not sure if thats proven with before and after dyno tests or just butt dyno commentary.
07-12-2007, 02:46 AM
#6
Higher octane fuel should net you some gains...
not the same gains you would get from a dedicated 100 octane program but if you log your IKC system you will probably find pull up to 8 degrees in warmer weather on 93 octane fuel. This should decrease with higher octane. Another possible solution as Vijay pointed out is intake temps likely related to heat from the high output motor packaged in such a small space. Heat exchangers may help this and become absolutely necessary in supercharging these motors, more so than adding a blower to an old 350 or some such. Indeed, MTM who is one of the only companies to successfully supercharge the S4, RS4, and I believe R8 is in testing found it necessary to not only add cooling by adding an additional water radiator but also they had to liquid cool the intake manifold. This is one of the hurdles companies like APR and VF Eng/GIAC are likely running into on even the standard 4.2.
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07-12-2007, 07:43 AM
#9
We showed that back in January with my 1st dyno runs
Resetting the ECU, which allowed the timing to go to full advance, after being retarded by something (bad gas, conditions ... etc), caused a gain of around 7 hp at the top end, and a proportional gain across the entire HP/Tq curve
This, however, was quite different than the effect of input air starvation, which your sources did not mention. Timing differences and corrections for atmospheric conditions will shift the relative magnitude of the HP and Torque curves on any Naturally Aspirated engine, but it will not change the shape of the curve. Input air starvation will progressively cause larger and larger percentage variation as RPM increases.
This, however, was quite different than the effect of input air starvation, which your sources did not mention. Timing differences and corrections for atmospheric conditions will shift the relative magnitude of the HP and Torque curves on any Naturally Aspirated engine, but it will not change the shape of the curve. Input air starvation will progressively cause larger and larger percentage variation as RPM increases.
