Fuel Trims during WOT

[xbrandino]

I'm unsure if anyone else is having this issue, or whether it even is an issue but I've noticed when recording a WOT my STFT is increasing from 10% all the way up to 30% as it approaches full boost and whilst in the pull to redline it is doing a STFT adjustment of 20ish%, at least that is what it says. My AFRs are fairly close on point but if I do the 20% correction in the MAF calibration my AFRs shoot very rich beyond 9s, despite it saying it was adding 20% during WOT.

And to add onto that, during the pull where AFRs were in the 9s it was saying it was adding 30% STFT. Car had traction off and wasn't slipping during the pull. Is this a tuning related issue or just something that the ECU "claims" it is doing but actually isn't?

[mituc]

Yes, it's normal for the WOT STFTs to be in the 20-25 range.
For the other case when the actual AFRs dive into high/mid even low 9s or high 8s it's because of traction or stability control (SWAS), especially if at the same time you will want the desired AFRs jumping to stoich even though at that load and RPM the target should be totally different.

[xbrandino]

Okay, thanks for the information mituc.

As long as my AFRs is matching my desired, everything should be fine? If I want to fine tune my AFRs do I use the formula Actual AFR divided by Desired AFR and ignore what the trims are doing?

[mituc]

You can apply the fuel trims formula only when the ECU runs in closed loop. For open loop operation (high POT or WOT) you will have to use the difference between the actual and desired. I usually apply a correction factor of 1 + 0.5*(Desired-Actual)/Desired

[xbrandino]

Okay sweet, will do that from now on.

How can you confirm the car is in Open Loop? APP > 75% or I just mentally know that I was WOT there so it'll be Open Loop.

[mituc]

There are several thresholds that will put the ECU into open loop. If you look under the Absolute Limits section you will see both APP and load thresholds. If one of those is exceeded then the ECU will start operating in open loop and will use the open loop tables for timing and fuel.

[xbrandino]

That is awesome to know, I really appreciate the help.

Is there a difference between tables 1, 2, 3, 4 and 5 or am I able to make them all the same with reasonable limits in place?

[mituc]

It is unclear to me when each of them are used... I usually set them all the same.

[xbrandino]

Fair enough, I'll let you know.

Aside from fuel trims, with ignition timing how aggressive can you make it when coming into boost to help increase the spool rate and what is a general amount of ignition you can get across the board with the stock K04?

My K04 seems to flow a good amount of air seeing a load of around 1.7 at 6000-6500RPM with only around 80% wastegate. Is there a point pushing anymore? (BATs do start to increase)

[mituc]

The amount of timing you can throw at the engine depends on various factors: pistons, fuel octane, contamination state, amount of blow-by recirculated back into the cylinders, and so on.

When increasing boost the boosted air temperature will also increase for various reasons:
1. law of thermodynamics: p1/T1 = p2/T2;
2. turbo speed generating friction with the air coming in;
3, heat transfer between the turbo components, from exhaust to intake, and so on;
4. radiant heat from exhaust, turbo, the engine itself, as the heat production increases with the higher amount of fuel burnt.
So it's not a linear increase as you'd expect when only applying the law of thermodynamics...

With these things mentioned, there is a certain threshold for each engine + turbo + fuel combination past which increasing boost and airflow will not result in an increase in power, and in these scenarios you will also hear about "knock limitation" or "fuel octane limitation".

The factory K04 as well as some other good aftermarket turbos (gen2 garrets 2867 and 3071 specifically, bnr S3, possibly others) will spool pretty quick and you may not need to be very aggressive on timing and fuelling (as in go very rich with AFRs and low on timing - both of these would also result in a lot of heat, even though only temporarily) to make them spool up.

The wastegate duty cycle is more of a measure for the EBCS pulsing that it has to perform in irder for the turbo to deliver the target load/boost. I usually push the K04s to 100 EBCS, however I often come across situations when from 75-80% WGDC to 100% there is little or no increase in air flow or boost because at 80% EBCS duty the turbo was already at its max. So you will have to explore with yours and see where it lands. I do not recommending revving too much past 6k rpm in such cases though, that little turbo suffers a lot. So shift at 6100-6200 (6300-6400 on the dash) and forget about the last 500-600rpm you still have until rev limit until you get a larger turbo.