Looks nice...but does 3" make sense? Custom RS4 exhaust

B6/7 S4/RS4
#41

BTW my next set of logs, i will do one with the car setup as is, weighing in at about 3720lbs. Last run i did pre-carbon clean, that was the car weight. Then I will put in the new seats, pull the rears, get the car to ~3540lbs, and do another run. Last run I did 7.33 seconds 3k-8k. Run before with slightly less carbon buildup and 3k less miles on the car, I did 7.29 seconds. I expect the be at or around 7.15 seconds after carbon clean, and then I expect to crack into the 6’s when i switch seats, remove rears. So think about that, a stock clean car does 8.5 seconds from 3k-8k. This car tuned and full exhaust, and lightened by 400+ lbs should go more than 1.5 seconds faster. Thats a ton. All on 92 pump gas.

Which means I should be able to get very close to 12.0 in the 1/4 mile if I can drive it decent. on 92 octane.

#42

How do you measure the 3k8k…the vagcom time. If you’re tuned, that may be different to stock time.

#43

When you log the car using vagcom, its just a timestamp for the data point. All data points have timestamps. As long as you look at the timestamp on the same data point (I use RPM), then you are looking at the time the data was captured in reference to when the logging was stared. Look at the output of the vagcom log, convert from .csv to .xls. Also make sure to capture in turbo mode!

Now the trick here is not all timestamps and RPM line up to the 3k or 8k targets. You may have normalize these by doing a bit of math, since across pulls, these need to be standardized to 3k and 8k to be valid for comparison. Take for example you have an RPM of 2940, and the next one is 3120 in the log. Since these are both timestamped, subtracting the rpm of 2940 from 3120 gives you a delta. 180rpm. take the offset for 2940 from 3000 and that gives you 60rpm. 60/180 = 33.3%. Now take the delta of the timestamps at 2940 and 3120. Multiple by 33.3%, and then add to the 2940rpm timestamp. That is your 3k timestamp, approximated, but very accurate because the rate of acceleration is very linear. Here is an example problem:

RPM Timestamp
2940 8.22
3120 8.49

RPM Delta: 180rpm
Percentage 2940 is from 3000: 33.3%
Timestamp Delta: .27 seconds
Percentage x timestamp delta = .09 seconds

Answer for 3000 RPM approximation: 8.22 + .09 = 8.31 seconds.

Now do the same for the top end and you can then subtract 3k approximated timestamp from the 8k approximated timestamp. This is your 3k-8k span. if you are lucky, one of the timestamps will be at exactly 3000 or 8000. Also to get smaller deltas, capture less data points. I usually do only RPM, timing, IAT, MAF and TQ, in Turbo mode. That is important, otherwise data capture is even slower. If you want to get the most granular data, take only RPM. But since acceleration is pretty linear, and you will still have to do some calculations, its not going to have much affect doing it rpm only or capturing a few extra points.

Whether you are tuned or not, the timestamps for the data are not driven by the tune, they are driven by the sampling rate of the vagcom and the USB speed. And yes, tuned the times are faster than stock, meaning the spans from 3k to 8k are less, but the method of capturing timestamps is the same. RPM is RPM, and the timestamp on RPM is as well, regardless of tune.