RomRaider

Does anyone see a need for per-gear initial/max wastegate duty cycle tables?

I've been giving some consideration to how something like this would be coded and it should be fairly straight-forward to implement but I wonder how useful this would be. Is this something that would be useful to help manage boost creep or spikes?

I know Merchgod has indicated there are per-gear request torque compensation tables but I haven't located them yet. I guess in a sense, if these per-gear requested torque compensation tables can be enabled and work as expected, having per-gear WGDC tables would likely be redundant.

Thoughts?

What would torque compensation do?

In their absense (or maybe either way once I understand) it would definitely be useful. I don't know anyone that likes slower spool in the gears they use and it would affect most.

As I said, I haven't found the logic yet, but as I understand it, per-gear requested torque would allow you to limit the maximum requested torque from the requested torque table(s), and since this value is an index into the WGDC tables, you could effectively reduce WGDC.

For example, let's say at WOT at 2800-3200 rpm you have a requested torque of 420 units. In your Initial/Max WGDC tables, under the 420 column, you are calling for 70-80% WGDC to cause boost to ramp up quickly. In 4th or 5th, you notice that boost is building too fast and you are spiking well above your boost target. This could be controlled somewhat by a carefully tuned TD Proportional and Integral, but if you had per-gear requested torque compensation/limiters, then tuning might be easier. With per-gear requeste torque limits, when you floor it in 4th/5th, instead of 420 units of requested torque, the tables limit this to 350, for example. Looking under the 350 column in your WGDC table, instead of 70-80% initial WGDC, you only have 40-50% and this should reduce your chance of overshooting your boost target in the higher gears.

What I'm proposing is per-gear WGDC tables. So your requested torque in 4th/5th would still be 420 units but now the ECU would lookup the initial WGDC from, for example, "Initial Wastegate Duty Cycle - 4th gear." In a sense, the end result would be similar but per-gear WGDC tables would allow you to have more control over the exact WGDC by gear and be more straightfoward since your throttle tables wouldn't have a compensation applied to them.

As I said, it's just an idea I'm throwing out there at the moment. Not sure if it is even useful.

The code should be failrly straightforward to implement and the per-gear ignition timing logic could be used as a model. Essentially, I'd create four extra initial/max WGDC pairs in free ROM and then alter the Initial/Max WGDC logic to jump to a new segment of code that would look at the current gear, then select the appropriate table, and copy the table address to the register used by the stock Initial/Max WGDC calculation code.

Sounds like fun. Personally I'd just like to set slightly lower target boost and WGDC in first gear to reduce wheelspin. There's some existing code in my 05 LGT ROM to modify the boost target, but nothing for WGDC as far as I know.

Also, I really like the idea of trying out hacks like this with boost control because there's a much much lower risk of blowing the motor if something goes wrong. The fuel-cut feature is there to guard against excessive boost, and if you hook up an MBC in parallel with the BCS you're even protected from that. Whereas, with the timing tables, one bad value could be a disaster.

Yeah, I was so nervous when I tested out relocating four ignition, two fueling, and four KCA tables so that I could add 5 more load columns to gain table resolution. I checked over my code about four times and decided to do a fifth check and discovered that I didn't align the start of one of the next tables on a 4 byte boundary. Not sure if this would have mattered but yeah, going WOT for the first time had me cringing. I kept waiting to see 60* timing show up and BOOM. lol. Everything worked though.

The STI/WRX has 1st gear target boost limiting too but, as you said, that isn't massively useful.

One of my biggest gripes with making changes to ECU logic is not being able to debug the code, optimize, or verify that all displacements/offsets are correct. As it is, I just grab code segments that appear to do what I want (move this register here or copy some value to an address, etc) then customize at the bit level. Not fun.

06-07 WRX ROMs (and likely others) have an "Active 1st Gear Compensation" for boost and it is applied while below a target vehicle speed, which sounds like what NSFW is referring to on his LGT ROM. While this doesn't directly increase WGDC, it does so indirectly by coercing the Turbo Dynamics to have more effect. i.e. due to greater negative boost error assuming you're running a positive boost compensation.
Taking this logic and expanding it to 2nd, 3rd... might be pretty easy at least with an 06/07 ROM. However, this strategy might only make sense for 1st gear since you'll likely never hit your target boost before needing to shift, whereas in 2nd you could hit your target, which would now be elevated with this boost compensation. So maybe just a table with a WGDC compensation for each gear. The question is what do you compensate? final WGDC? Initial WGDC before TD is applied? just TD proportional? From a control system standpoint I think the system is loosing some damping as opposed to stiffness when you boost in a lower gear...so which term(s) do we adjust to compensate? Been awhile since I've dealt with control theory so I could be completely wrong here...

Typically you tune the boost for 4th gear (on a 5 speed) w/o overboosting and thanks to the flexibility that turbo dynamics provides it gets you decent performance in 3rd, while 2nd suffers a bit because if you tuned to hit boost down low in 2nd you'd overboost in the higher gears. MickeyD has some good plots of 2,3,4,5, boost curves in some of his posts.

The JDM ROMs have this. It would be awesome as you can ramp up wastegate in the lower gears to get faster spool and higher boost levels while not having to worry about overboosting in the higher gears.