Suggestion on setting manifold geometry, VTC, etc.
Posted: Wed Oct 29, 2008 1:16 pm
The J30 VG30E Maxima has a variable geometry intake manifold that closes little trap doors between ports 1-3-5 and 2-4-6. Normally the door is open, but at certain TP and RPM ranges it closes, creating what are essentially two intake manifolds.
Since I've changed cams, I figured this would no longer be optimized. Turns out that's true. The stock switch-over is 3500, now it looks to be more like 4000.
To tune this, it seems to me what we're actually trying to measure is airflow, not power. Since you can't expect the tune to be optimal for the different geometry settings, measuring the airflow illustrates the potential of the engine (air pump), rather than how good your tune is.
Thus, forcing the manifold (or cams) into your boundary states, which in my case are open and closed, then logging MAF, you find what the engine is capable of flowing. Adjust the VTC numbers in the ECU, then get back to making power.
I understand that there might be some hit to boost onset due to tuning at one geometry vs. the other initially, but this method should get most application quite close with a minimum of fuss... And no need for a dyno.
Since I've changed cams, I figured this would no longer be optimized. Turns out that's true. The stock switch-over is 3500, now it looks to be more like 4000.
To tune this, it seems to me what we're actually trying to measure is airflow, not power. Since you can't expect the tune to be optimal for the different geometry settings, measuring the airflow illustrates the potential of the engine (air pump), rather than how good your tune is.
Thus, forcing the manifold (or cams) into your boundary states, which in my case are open and closed, then logging MAF, you find what the engine is capable of flowing. Adjust the VTC numbers in the ECU, then get back to making power.
I understand that there might be some hit to boost onset due to tuning at one geometry vs. the other initially, but this method should get most application quite close with a minimum of fuss... And no need for a dyno.