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Discuss all things tuning in this section. News, products, problems and results.
It's probably best if you let us know which VTC system your talking about.
For total simplicity I'll describe the way to tune switching points on a Nissan NVT system, it only has 2 positions.
First with the system in one position complete a full dyno sweep run, then repeat the run with the system in the other position. Once complete you overlay the two graphs and the positions that give you the most gains are when the stsem should be in each position and cross over points are your switching points.
On systems with more positions you need to repeat this process with each over the cam positions
what i was talking about is the two position switch, but the problem is when i first tune and push the car when the vtc is off the lambda seems fine (around 12.5) but when i turn it on it goes lean ( around 15 sometimes 16) so i cant usaully complete the the run
Then you'll need to create a second fueling table for when the NVT active, which ECU are you using?
I am runing the car on a motec m800 ecu, after i set the the trigger of the vtc and closing of it i would tune the car for the desired lambda but what i mean is should i tune the afr after runing the vtc and then compare the graphs?
The VTC system is designed to adjust the cam timing to help optimise engine VE across a wider rev range than a fixed cam timing can offer. If you engage the VCT and the AFR goes lean, this indicates that the VE has improved because more air is now entering the cylinder so this is a good thing. What you'll need to do is compensate for the improved VE by increasing the fuel delivery.
I'd suggest just roughly getting your AFR close initially and find the optimal switching rpm. Once you have that sorted you can then fine tune the AFR