N54 Scaled load to boost relationship help

[langsbr]

I promise I have reviewed every thread I can find, as well as used V8Bait's tuning guide, but I must be missing something with regards to load and boost.

With the N20 TMAP, I understand that the MAP scaling (and thus load) is normal up to 10 PSI, and above that breakpoint it has less resolution. I also understand that the maximum amount of boost is 37.2 psi based on the 3.5bar map sensor and voltage scaling. My understanding (possibly incorrect) is that max load is 220.

Using V8bait's spreadsheet, 10psi is 145 load, and thus above that, I'd expect scaled load values. What I am not able to grasp is what load corresponds with what boost, at least not when I look at my logs For example, a recent log has actual load of 172.4, and boost was 21.7psi. Based on my math, I would have expected a load of 172.4 to be around 20psi instead of closer to 22 psi.

I would have expected 22psi to be 178 load. Granted my math is likely wrong, but the method I used was calculating the slope of the line above 10psi, which I got to be .36 and y intercept of -42.2.

I don't know why this load based tuning is so hard for me to wrap my head around - perhaps I'm overthinking things expecting it to be exact but it just isn't clicking for me.

I'n not looking to be spoonfed, but rather to understand the complexities. I'm not averse to reading, it does just seem that the majority of information is 5+ years old and no longer truly applicable with all the tuning updates.

Thanks

 

[KClemente]

From what I understand, you basically just gotta go with the flow unless you want to plug everything into a granted not-so-complicated formula.

Load vs. Boost can vary depending on boost request offset and physical vanos targets.

That's just me though, I could be way off in that explanation but I never really looked at load other than to know where in my maps the dme is referencing.

 

[carabuser]

I think Load is just a measure of cylinder fill. So 200 load is 200% air (100~ would be the limit of a non FI car).

The load target is a percentage of cylinder fill. To reach that cylinder fill the DME turns into a boost pressure target using a volumetric efficiency value which it then attempts to meet using the wastegates and throttle.

The problem is exactly what you're seeing. Because Load does not equal boost you have imperfections introduced in any table that references load. I'd also expect it to completely fuck up anything referencing torque. This is basically how the JB4 operates and the reason why JB4 cars drive like shit. It's ok for people who just use their cars for drag racing but makes for a bad daily driver.

 

[mj6234]

From what I understand, you basically just gotta go with the flow unless you want to plug everything into a granted not-so-complicated formula.

Load vs. Boost can vary depending on boost request offset and physical vanos targets.

That's just me though, I could be way off in that explanation but I never really looked at load other than to know where in my maps the dme is referencing.

What he said. You also have to remember the same load wont correspond to the same boost target due to things like IAT. Boost target is definitely lower in 0* weather vs 90*. What values you use for the MAP sensor conversion matter too. From the formula I made, boost was maybe 1-2psi higher than I expected it to be, but as KC said it doesnt really matter. It is just a reference point to set your other values (timing, fuel, etc).

 

[tony@codewerx]

And then there’s the boost limit multiplier …