here is the cam specs:
the stock VVT maps can be accessed in the ecu and are as follows. However PLEASE NOTE that the exhaust retard has been mistakenly named Intake Advance and vice versa.
stock AVCS tables
I noticed the intake AVCS tables have 50* of advance stock at low-mid RPMs. The exhaust has been retarded at about 20-30* at ~2000rpm.
Now from my readings I have found that Advancing the intake whilst retarding the exhaust actually increases overlap which results in poor performance and reversion. Advancing both intake and exhaust however should create low end torque. So why has subaru retarding the exhaust cams at low RPM while intake is fully advanced? So opening the intake further after BDC (more advance) and opening the exhaust valve sooner before TDC (advancing the exhaust) will definitely give more torque no questions asked.
Using engine analyzer pro software, the theoretical best overall valve timing for low rpm performance is 45* advance on intake and 10* retard on exhaust:
so in the ECU this would translate to getting about 90% of advance possible on both the intake and exhaust side. This is very similar to factory AVCS on the intake side, however the exhaust side is still too retarded on the ECU.
31* of intake advance and 14* exhaust retard gave best theoratical mid-high range in the software.
only 15* of intake advance and 20* of exhaust retard gave best results for +5k rpm
So theoretical conclusions from this suggest that:
A. Intake timing is well tuned from factory, however maybe a little too advance at low RPMs
B. There is no reason why the exhaust should be retarded at low RPM and fully advanced at midrange.
I did get a chance to take the car on the dyno and to test out the theory above. I only had time for a few pulls and here is what i observed for now:
- retarding the intake tables at higher RPM hurts performance throughout the revrange
- retarding exhaust by 10* at high rpm (from 0) made no difference in output
- advancing exhaust at low RPM degraded torque
- ignition/fuel was not changed
So i'm confused whether this car is already tuned at its best or perhaps I'm just not going about the right way in tuning VVT.
I have heard that retarding intake can allow one to run more ignition timing and hence make more power.
1. I'm just curious why the intake has been fully advanced at low rpm and exhaust retarded. Does intake advance and exhaust retard create more low end torque?
2. doesnt exhaust retard create more midrange torque? Why is at low RPMs exhaust retarded?
3. Why does retarding intake just by 5* hurt performance at high RPM? Should we perhaps even advance intake further?
4. overall what would be a better strategy to tune for power next time on the dyno?