So…I had a problem with a knock sensor on my RS4 that required removal of the manifold for Audi to replace it (warranty). I took the opportunity to have them clean the carbon since half the labour was done. After being quoted $1000 to have the carbon clean done at 3 different places including the dealer, I figured if I could get it done for about half that, great. Sure enough…$450 was my part, so I said ‘go ahead’.
They kept the car overnight and also did the oil and spark plugs as well as the rest of the 85,000 KM service (I have Audicare 
).
Before I handed the car to them I did a 3k-8k test, as well as logs and pbox testing. I will focus here today on the 3k-8k testing and then we can look at the other tests once I do the ‘after’ on those. From a butt dyno perspective…I noticed almost nothing. I was a bit surprised because lots of people rave about the massive difference…the 5500 RPM kick…etc. It should be noted that the 5500 RPM kick is largely the torque limiter putting a throtttle restriction on the car up to…you guessed it, 5500 RPM. In the hot summer conditions however that kick is much less noticeable because the torque limiter on a stock car is not likely to be met due to shit DA. So your throttle is pretty much wide open from idle to redline if you slam the pedal. This is one of those simple details that people don’t know about this car, but then leads them to make sweeping statements about ‘I’ve lost the kick, I must have carbon!’. No, it’s just summer. Have a pina colada and relax.
Here’s the 3k-8k before/after comparison:
BEFORE
Temperature : 80.6 fahrenheit / 27 Celsius. (the car thermometer said 28.0 C)
Elevation: 370 feet
Barometric Pressure: 30.04 inches hg
Relative Humidity: 70%
Density Altitude: 2345 feet
Oil Temperature: 107 Celsius / 225 fahrenheit
3k-8k 9.0
3k-8k 9.2
https://www.youtube.com/watch?v=KxlrEoOXjmQ
AFTER
Temperature : 75.2 fahrenheit / 24 Celsius. (the car thermometer said 22.5 C)
Elevation: 370 feet
Barometric Pressure: 29.92 inches hg
Relative Humidity: 74%
Density Altitude: 1801 feet
Oil Temperature: 93 Celsius / 199 fahrenheit
3k-8k 8.4 seconds
https://www.youtube.com/watch?v=f8BDSMG7JMY
So there is definitely a performance difference from yesterday to today, however we have to keep in mind:
- 500 feet of density altitude is pretty significant
- cooler car overall…yesterday oil was 107 and today it was 93. Heat soak yesterday would have been worse as the car had been driving for about 15 minutes before testing, whereas today it was more like 5-6 minutes
Still, the gap is about 0.7 seconds. Doing the 3k-8k in 8.4 seconds is quite good in cold temps…let alone 24 celsius and high humidity.
I will look for another day with temps where they were yesterday (27 or so, and 2300 feet od DA) and retest. I will make sure the car is a bit hotter too to take that variable away. I will also do a bit more testing including 60-130 (this will really show the difference as it is my belief that high RPMs is where carbon really costs you a noticeable amount of performance, and in a long sustained pull at high RPMs, that should show up pretty significantly.
If I were a betting man, I don’t think I would be much quicker at the quarter mile. Probably same as I ran last year when I was stock. I don’t know that I will bother to go to the strip to test it (we already did that with Mistro’s car and it was a nominal difference)…but I will do some pbox 1/4 mile stuff and compare to old pbox 1/4 mile results I have on file.
