There is one slightly simpler thing you can also do.
Not as good as measuring both positions on the dyno, but it works quite well in my experience.
Dial in the cam switch, do a pull. Note load (rl_w) at the switch point.
If:
* load before the switch point was higher, and it gets lower after the switch point, then your switch point is too early;
* load before the switch point was lower, and it gets higher after the switch point, then your switch point is too late;
* load remains flat, then your switch point is in the right spot.
As an alternative to measuring load, you can measure acceleration (delta speed vs time) and do it that way, but I have found that usually looking at rl_w gives good results.
It took a bit longer to start on this due to some fueling hardware issues, but this week, I took a couple of steps into vvt tuning on my RS6R car with 2.8 Heads and Cams. I started by zero-ing out KFNW. The car felt slower, and boost built much slower.
So I went the other direction and added the RS4 K-box KFNW values and rpm axis (cam change-over around 5200 rpm) and this is what I got: Acceleration increased, boost hit harder, and you can see in the graph that even though actual boost is flat, at the switching point and a bit beyond, load is decreased. It appears that some overlap is having a positive effect at the switch over point.
Resolution is low, so I attached the log as well.
Green is Desired Boost
Red is Load Acual
Purple is Boost Actual
I'm a bit scared to keep the cams advanced much higher in the rev range, but hell, if it keeps making more power, then why not? Well,
my thoughts on one side are, in theory, so long as the belt and chains are attached, it shouldn't matter how quick the motor is spinning. If the valve has not moved into the path of the piston at 4000 rpm, then it shouldn't at 6000 rpm either, right?
On the other hand, the 2.8 NA intake cams overlap the exhaust valves longer to begin with and with an additional 20* of advance, it seems like if there was going to be one of the three (RS4, S4, 2.
that may have a problem, this would be it.
Any other thoughts? Am I interpreting the graph correctly?
I looked up a Passat 2.8L ATQ file today and found KFNW and KFNWWL maps to compare with RS4 K-box since ATQ heads are what I am running.
Interesting to note the NA cam angle strategy is nearly the opposite as the S4 and RS4. Note also that cam switch back to normal position takes place at the same RPM as the S4. Was audi concerned about smacking an intake valve at high RPM in this file as well? Now what about the warm-up vvt map for the RS4. Shows that Audi had no issues running the cams advanced through redline with the RS4 cams.
Has anyone else rapped out an NA heads/cams car with the cams advanced through the rev range?
