RomRaider

My incidents of hitting the "boost cut" happened at right about 1000mg/stk also. I think we are onto something here!

I'm unsure what everyones experiencing but 1000mg/strk seems a bit high for 7-8psi. Who is running what MAFs and in what configurations? I see pazi88 is running Euro/540 with 2.2k resistor which I would assume is in a draw thru setup?

Yes draw through. Checked the logs and it seems that the MAF scaling is bit on high side. It's reading about 700kg/h in that particular problem point. but in reality it's somewhere around 630-650 kg/h. Which brings load lot lower. But still it doesn't give much headroom for more boost.

Mines more like at 15psi.

Running slot maf, 2.2k resistor, blow thru. Scaling in my scaling thread.

Do you have any WOT logs? Today we got the car running full WOT pull without problems. I basically used 1k resistor scaling for MAF with 2,2k resistor attached in MAF. Did some excel magic to scale all maps accordingly and now it seems to run fine.

Previous 1000mg/stroke loads are now ~600mg/stroke loads. The real figure is probaply somewhere between those two, but this gives more headroom for more boost. And in normal driving coditions the error in load shouldn't be more than ~50 mg/stroke, so all other things that rely on load calculation should still work fine. (Resistor scaling has lot less effect on low maf walues than high maf values)

I haven't had a chance to play with car stuff for several days now, but I can answer this question. I'm running the ubiquitous Nissan MAF in a blow-through 3" tube, with a 2.2k resistor. With the initial MAF table I used from ba114, air flow values were much lower. That would be dandy to me other than for the sake of my automatic trans, that I believe relies on the load value reported from the DME to determine line pressure and shift firmness.

My WOT shifts were noticeably mushy and slow with the lower reported load numbers, and it just felt like the trans wouldn't last long at all. Consequently, I adjusted the entire MAF table until I had reported loads at least as high as they had been with the factory MAF.

My feeling is that I can stretch the scaling of the MAF above the normal WOT values to give me more headroom for additional boost, but the question remains, why are we having this issue? Seems like we can't use over 1,000 kg/hr currently, even though we have 2048 kg/hr tables..?

The max kg/h value depends on the RPM as ypu can see from the table by mrf582. For example at 5000 rpm, the 1200kg/h level was not problem at all. But it's strange that the max load value is lower than in the table.

Right, it seems to be a load limit thing, not an airmass limit thing, right?

This spreadsheet i posted last year demonstrates why and what is happening

Not any proper logs of WOT yet. I've been more focussed on getting idle and lean cruise trims in check first. These occurrences happened by accident.

My wideband controller has stopped working too so need to get that working again before i do any WOT work

ba114, I'm not sure what you're saying, that you are speaking of theoretically what you expect to happen based on your spreadsheet but haven't tried it out yet? Pazi88 and I seem to be experiencing similar unexpected behavior that I don't think fits with your spreadsheet. Sorry for my confusion, but I'm just not following...

Assuming that you are simply speaking about what your spreadsheet predicts, I still don't understand why it happens? For instance, if you look at the following two instances of when I have hit the boost cut that seems to happen for me just over 1000 mg/stk, I don't understand where the load limit is defined like the 1389 you have defined in your spreadsheet? If it's a function of where the MAF table calculated together with RPM simply runs the load level out of out of the airmass table, how do you know that would cause a boost cut behavior?

When I'm hitting My "boost cut" limit/load limit/whatever limit it is, airflow is at a very low level compared to the 2048-ish max airflow ***I think*** I have defined in my tune. In hopes that maybe I have something messed up, I've attached my 24kb partial tune file, and my most recent 256kb tune that the partial is based from. In that full read, the bubble for "MAF Mode=2048kg/hr" is highlighted.

Any light you can shed on this is much appreciated!

Oh, and here's some sounds of boost of the very car that generated those logs. On this run the small diameter rear tires were allowing too much slamming into the rev limiter, so I had trans limp mode going on with some bogging in a couple of places, but it's the only video I've seen posted of any of my runs so far:

https://www.youtube.com/watch?v=0sDOBjHeILM

I cant explain the behavior in your logs. The spreadsheet simply highlights where you would be exceeding the DME load limit (1389mg/stk) based on the calculation of

The 1389 mg/stk is a hard limit in the DME. Its not defined in any tables.

The spreadsheet shows the theory i.e. anywhere in the red would cause this issue, however i have personally experienced the "boost cut" while logging.

Sigh. Do we dare change the way that value is calculated? I see roughly 950 kg/hr with 10psi and have not had any of the issues described here. I doubt ill reach the limit with my goals/restrictions.

If so every other load value in the DME that shares the same calculation would need to be modified. Or we might be able to copy the chunk of code to an empty space in the DME as a "one-off" calculation.

Maybe i'm thinking too rudimentary here, but if we simply enabled 2048 mode and halved the MAF table values we would reduce the possibility of this happening?

It would mean the reported load would be 50% of actual load, but atleast we would reduce possibility of hitting the load limit.