We have been kicking around this subject in another thread and decided it needed its own space.
According to some sources, VCT action, even in stock trim, is responsible for a lot of the output:
https://www.fordnxt.com/news/how-muc...-the-question/
With forced induction, and positive manifold pressure available to fill cylinders, and also a higher risk of loosing boost
from blow-through (during valve overlap), the optimum angles are most likely quite different. What range of values are
we talking about? Hopefully we can find out.
Obviously, strapping onto a dyno for a nice long session, with a solid plan to test all sorts of angle combinations, would
give you some nice data to pour over and determine optimums at each RPM. Not everyone has that option, and the fact
that we can't "live tune" the VCT settings definitely slows that process. I think we can come up with a protocol that allows
road based logging to give us direction on this.
Here is what I have rattling in my head:
- Pick a set of IVO/EVC angles with a LSA that has no positive overlap (ensuring that we have no blow through)
- Make the OP VCT tables equal to this angle set for all RPMs
- Log a WOT run that includes (at least) MAF rate, RPM and boost pressure (I have a mechanical gauge, so I gopro the
boost gauge alongside my nGauge to get pairs of RPM vs boost)- Now advance that angle pair to keep the same LSA and make another run
- Repeat this process for a number of different angle pairs advanced and retarded from the first pair
Looking at this data, we can plot boost pressure (or potentially MAF rate) against RPM. Minimal boost pressure should signify
best cylinder filling, which would correspond to highest MAF rate. Theoretically, the "best" angle pair would vary with RPM,
so you could pick the best angle pair vs RPM and composite them together to populate the OP VCT tables, maybe smoothing
somewhat if the transitions are big.
From there, we could move to optimizing the exhaust valve closing, by retarding it until the onset of blow-through. Similar to above:
- Make a baseline run with our new VCT angles
- Fix IVO angles and add a static +5* or +10* to all EVC angles, run again
- Repeat
At this point I think we need a measure of boost, because the MAF sensor can't differentiate between air combusted and air
blown through. It's possible that you would see STFTs increase, but I don't think that is precise enough. Basically, we would
now be looking at boost vs RPM and any reduction in boost, compared to our baseline, would be from blow-through and should
be avoided. You would pick the maximum EVC angle which did not reduce boost and store that in the table.
This would certainly be a more coarse approach compared to dyno runs, but I think it would net good data and get you much
closer than guessing or copying someone else. I'd love to hear any input on refining this method.
So for picking our baseline angles, we need to know where to start. Here is some info posted by others that should help get us
there. I'd love to hear the actual values listed confirmed, since I'm not an expert in Coyote cam specs:
From Mr. bbrooks98, an awesome excel worksheet. Validation of the calculations and values here would be nice as well: