Part 2:
Understanding the Logs
Accelerator position (%): Pretty self explanatory. In terms of logging, we typically want to look at what the car is doing under wide-open throttle (WOT). On most cars this is in the 93-95% range. It is perfectly normal for the car not to hit 100%. For accelerator and throttle positions, the car will adapt to the given range on each vehicle.
Engine speed (RPM): Again, pretty self explanatory. This will give a good reference point in the logs when the car is at maximum performance/higher RPM’s. Like WOT, the best indicator of performance is going to be what the car is doing at higher RPM’s; say 3000-7000 RPM.
Charge air pressure; specified value (hPa): This is essentially what the ECU is requesting in terms of air pressure or boost in the case of the B8 S4 engine. This value is in hPa, and needs to be converted to PSI for more common interpretation. You also have to subtract the ambient air pressure to get the actual requested boost number.
1 kPa=10 hPa
1 hPa=0.014503774
So, to calculate the requested boost:
Requested boost= (Charge air pressure; specified value hPa) - (Ambient air pressure kPa x 10) x 0.014503774
**On a stock tuned car, this value will be in the 12 PSI range max. Any boost over this amount will trigger the bypass valve, and be bled off.
**On a tuned car, this value can be as high as 18-19 PSI. The tuned cars request more boost than is possible to ensure there is no bypass. The goal of a tuned car is to use all the boost available without opening the bypass valve.
Intake manifold pressure; absolute (hPa): This is the actual amount of pressure in the manifold where the specified is the requested. So, like the specified value, it needs to be converted to PSI, and subtract the ambient pressure. The amount of actual boost will depend on the size of the pulley, and losses due to belt slippage or leakage, environmental conditions, elevation, etc.
Actual boost= (Intake manifold pressure; absolute hPa) – (Ambient air pressure kPa x 10) x 0.014503774
**A stock car will see boost in the 10-11 PSI range, but it will bleed off at higher RPM’s.
**A stage 1 car will see boost in the 12 PSI range, but it should not bleed off at higher RPM’s
**Stage 2 cars can see as much as 16-17 PSI. I have seen a max of 15 PSI, but that is in really high DA’s and we’re at about 600 ft. above see level (as we covered here, hotter/less dense air will make slightly less boost).
Air mass (kg/h): This is the amount of air the car is taking in via the intake. The environmental conditions and type of intake you have will effect this value. Obviously more air can equate to more power, so the higher the better.
**I have seen the stock intake have around 1100 kg/h maximum in my logging (70F, 50% humidity, 2000 DA). Aftermarket intakes that use the stock airbox are in the 1100-1200 kg/h range, and aftermarket open intakes like the Roc-Euro and CTS are in the 1300-1400 kg/h range.
Intake air temperature (degrees C): Another one that is pretty self explanatory; just note that it is in Celsius. IAT’s have a big impact on performance. Higher IAT’s mean less dense air, less timing, and the chance of more knock/timing being pulled and other bad things like misfires. The lower the IAT’s, the better.
**During my logging (see conditions above), I typically see a max of upper 60’s and low 70’s with the stock airbox. With the CTS intake (open filter with heat shield), I typically see in the 50’s.
Ignition angle; actual (degrees): This is the total requested timing. It can also be the total actual timing IF no knock is detected/timing is pulled.
**A tuned stage 2 car on 93 octane should typically sees total timing in the mid to upper teens at higher RPM/WOT. I see something in the 17-18 range on 93. On race gas those numbers can be in the low to upper 20’s in some cases. I see around 22 on 100.
**I don’t have logs for a stock car or 91 octane, so I cannot comment on those at this time.
ING_AD_KNK_x (degrees): This is the amount of timing being pulled from the given cylinder (x) due to knock detection. The amount will wholly depend on the gas you use, the condition of your car, and environmental conditions. It is very possible (and good) not to see any timing being pulled.
**Something in the -3 to -4 degree range is “normal” in hot temps or with lower quality gas. I have seen timing pull as high as -7 to -8 degrees on my car which will absolutely kill power. I am still trying to figure out why my car is pulling that much timing in some cases. Some of it is definitely the hot humid temps in Texas, some of it is the gas I was using, but even beyond those factors, that is still a lot of timing being pulled for a stage 2 93 octane car (I saw similar numbers on my 100 tune with 104 octane gas).
RFP_AV (%): This is the bypass valve opening percentage.
**A stock car will see significant opening because the car will typically make more boost than requested at higher RPM’s, and the rest is bled off—this is why stock dynos die off after 5000 RPM.
**A properly tuned car should see nothing here; 0%. Anything else means the car is not making max boost/power. There are some instances where a tuned car may bleed off boost. I’ve seen this happen on my 1-2 shift when I get wheel spin, and others have reported it with IAT’s get extremely high as a protection mechanism.