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I have been tuning on the motec m150 for a bit on a supercharged FA20 engine. I have been following the recommended procedure to tune the VVTI but realized that on my setup, changing the cam angles affects boost level. Boost level drops as I increase overlap which means I am going into lower load ignition timing cells where there is more ignition timing. I am wondering if it is now hard to discern what power increases are due to cam angle and what are due to ign timing advance/boost level change.
Do you recommend setting the ignition timing to be the same value (lets say 15 deg) at say 180, 200, 220 kpa for any given rpm (for example), so as to keep the ign timing constant in that column while you alter cam angle which also alters boost level? Curious to hear anyone's thoughts on this.
The way I have been going about it is:
1. I set the timing map conservative (~4 deg less than theoretical max).
2. Set both cams to 0 adv/ret. Do pulls at increments of 5 deg with the intake first.
3. Set intake cam to optimal timing based on dyno.
4. Do pulls at increments of 5 deg with the exhaust.
5. Set exhaust cam to optimal timing.
6. Verify that the intake cam is still in its optimal timing now that the exhaust cam is tuned.
7. Incrementally raise the ignition timing until MBT or knock threshold.
At steps 2 and 4 boost is fluctuating so i am worried I am not receiving the correct readout for cam angle optimization as it is going into different ign timing zones and the ign timing table is not optimized because the cam tables are not optimized yet.
Yeah I would say set each RPM to the same spark advance regardless of load will help. As you advance intake cam you change filling time and effective compression ratio, and also overlap, which can affect knock. As you retard exhaust cam you change overlap as well, and could be causing some scavenging.
I'm assuming this is centrifugal supercharger, so the compressor wheel speed is fixed. Let the boost go up or down (again as residual gas content and effective compression ratio/filling time changes). It's not a turbo so you can't adjust anything.