Discussion and questions related to the course Boost Control
I have watched both webinars "70 - Electronic Boost Control on the Link G4+" and "45 - Setup and Tune Open Loop Boost Control - Link G4+/ViPEC" (so please let me know if this is already covered in one of the other webinars or forum threads) and had a question about target boost strategies.
I am soon going to install a Mac 3-port solenoid to be controlled by my Elite 1500 in a closed loop setup (more because I would like the ability to switch between target boost values easily at the track, which I think is a lot harder with open loop on the Haltech), however my car currently runs a HKS EVC6 electronic boost controller which does not have the rpm inputs connected.
As such, the current EVC sees pretty severe boost taper on the HKS T04S 0.82 setup on my FD3S. For example, peak boost would hit 0.98 bar at 4500rpm and taper out to 0.8 bar at 8000rpm (you can see in this video from the track https://www.youtube.com/watch?v=px4L_eZXNXg).
But I began wondering why everyone aims for a constant boost value and to eliminate the taper. In the case here, my limitation is the stock injectors, which are running at around 90% duty cycle at redline (effectively, wide open - which the side feed FD3S injectors apparently can actually handle). So the boost taper was actually giving me significantly more power down low than what I would get if I ran with a constant boost value to redline.
If we're trying to get the most out of an engine setup, why don't we intentionally dial in boost taper so that at each rpm range, we are effectively maxing out the engines capabilities to its limits - whether they be knock limited, compressor limited or fuel limited? Is it just a driveability thing?
It really depends on the use of the car, I have seen people who run in power to weight specific classes use boost taper to 'cap' their horsepower.
Then again it can also come down to mechanical sympathy, loads of torque in the low down/ mid-range areas can bend rods so holding a consistent boost level allows precise control over the torque developed.
Another reason could be for traction and driveability, I'm currently building a high BHP FWD car and will be feeding the boost in higher further up the rev range to allow better control over traction.
It's a great idea if you can put all that power to the ground, my own car will only get manageable traction 1st and 2nd gear on 17-18 psi if I give it any more it just stands up n smokes the tires which makes corner exits exciting but dangerous.
The rear suspension really does need time to absorb the power we're feeding it.
As others have noted, it's totally dependent on what you're trying to achieve. As with many aspects of tuning, there's no right or wrong way of choosing a boost target, and what may be perfect for one car would make no sense on another. Provided you understand the implications of what you're doing, you can make an informed decision as to what's best for you. in the case of your FD3s with the boost tapering down, this probably would be an ideal scenario given the fuel system limitations (assuming the big spike in midrange boost didn't result in traction problems.