Fine tuning Cruze

[TurboGT]

Hey all, i'm new here. Been doing some digging on these forums and the internet in general and not quite finding what i need. Got a 2012 Cruze 1.4 automatic with the zzp big wheel turbo and supporting mods. It's been e-tuned by a professional, but he has left the file unlocked and i'm looking to make a couple very minor changes.

When on the highway, either when slowly accelerating or climbing a grade (i'm talking 10% throttle or less) the turbo will begin to spool, naturally. Upon letting off when desired speed is reached or cresting the hill, there is an aggressive amount of compressor surge. If you lean onto the throttle harder in this situation and build more boost, the BPV operates normally and everything is good.

Under the turbocharger tab, "part load open" is currently set to 125kpa or 18psi. I'm assuming this is absolute pressure, right? So the bypass valve currently wont open until around 3.5psi boost is reached.

So if atmospheric pressure at my elevation (1000 ft) is 95kpa, should i try setting this to 100? 99?

Any pointers would be appreciated!

[sprinto7]

IDK, but I'm guessing 125 is stock.

[TurboGT]

So after numerous changes today, I landed on -100 kpa (adjusted from -125kpa) on "pressure grad neg" and 105 kpa (adjusted from 125kpa) on "part load open". Honestly I don't think it made any difference.

The BPV seems to open easily when driving up my driveway in 1st gear and any other time, but it's just that one situation, 6th gear, tq converter locked, turbo slowly builds up some serious RPM, light lift of the throttle where the turbo barks pretty badly.

Maybe it's just the nature of this turbo?

Anybody have any input?

[jmardlin]

I haven't seen this with mine and I have the same ZZP big wheel V3 turbo unless you have an earlier version of it. My car is a manual trans though. I'm not sure if that would make a difference in just letting off the throttle a little though. I'll have to take a look at the settings on my 15 and see if it is different. I know the driver demand table is way different from auto to manual. A manual brings power in a lot faster than the auto does in stock tune anyway.

[jmardlin]

I looked at my tune file vs stock and those are unchanged but the surge limit is bump up slightly and the compressor speed is lowered some. Do you have an aftermarket air box where you can hear the turbo more?

[TurboGT]

Thanks for the reply!

The car does have the v3 turbo, non ported. I believe it's the most recent iteration, i had originally put it on in March of 2021 and then a warranty replacement in April of 2022.

I wouldn't expect any manual driver to ever operate the engine in a way that the auto does. Meaning, as low as 1500rpm around 45mph (in this case 6th gear tq converter locked). It will hold the gear when you demand a little more torque when you hit an incline versus downshifting. On the highway it's the same deal, holds the gear and builds a small amount of boost on an incline, which is where the condition happens (after cresting the hill and letting off). Myself, I'd never be operating the engine in this low of rpm range to begin with if the car was manual. I'd be downshifting to hit these hills or accelerate. So this is surely part of the reason you don't experience this.

Yes the car has a k&n hot air intake. It's very loud. In hindsight I'd have kept the stock airbox, although I'm not sure it is capable of flowing the CFM this turbo demands.

[jmardlin]

I downshift if it doesn't hold speed but I never run it at 1500-1600 in any gear. I don't have surge even if I give it a little throttle and build a few pounds and let off. Did you data log it when it does it. You might be hearing it just because of the airbox. The maf in these cars are easily damaged by using an oiled filter like a K&N. The stock setup can likely feed it to the max of that turbo.

[TurboGT]

I did datalog a while back. Nothing out of the ordinary that I noticed, aside from a little maf noise when it surges.

So my main concern about the stock box was the MAF tables. The k&n is supposed to be a perfect stock replacement but I'd be afraid to install the stock box and have the MAF read differently and cause issues with metering (mainly leaning out under boost).

What are your thoughts on this?

[jmardlin]

Every maf I have seen, in any car, all vary from car to car. Mine was lean below 20 grams/second and gradually got richer as flow went up. So essentially it read lower than actual flow at low flow and very close at 25 g/s and up.

[TurboGT]

Right, I get that. I'm just saying this car was custom tuned with the k&n intake installed already. If I switch to the stock airbox, the airflow may be slightly different through the throat where the MAF sensor sits. My concern would be the intake change creating a metering change at the MAF, that would in turn make an undesirable fueling change. Since the car has a narrow band sensor on it I wouldn't be able to monitor AFR accurately to make sure all is well in that regard.

[jmardlin]

Yeah I understand. Going back to the stock maf table. That is actually in the sample tunes that I got when I installed VCM Suite. I doubt you would ever see one of these cars go lean under load unless you ran out of injector. That is easy to do with the stock injectors but you can't do it running 42's with gas or 60's with E85 unless you are flogging it to within an inch of it's life. They are calibrated very rich under load from the factory and incredibly rich if you hit turbo or catalyst over temp protection. But yeah definitely don't want it lean under any kind of load.

[TurboGT]

So are you saying that this car should still be under stock maf tables then? It is tuned on 42#injectors and pump gas, which I thought required a skewed maf table?

Do you think I'd be okay putting the stock box on? Any way I can indirectly check to verify things are kosher without the use of an aftermarket wideband gauge? Maybe log MAF g/s and injector pulse width before and after the intake change to make sure they match?

[jmardlin]

I can't say for sure if they are or not. It is easy to verify if they are if you have the stock tune file. I know I have a copy of the stock 2012 1.4 Cruze automatic in the sample tunes. You could load your tune and load that in as the compare tune file to see. Injector size isn't changed with the maf table. Injector flow has it's own table that has the flow rate at various fuel pressures. The maf table can be used to fine tune fueling for different airflow amounts by changing the airflow up or down for a give maf frequency. Without a wideband you can't be absolutely sure of fueling. You can tell by looking carefully at the tunr that they intend them to run very rich under load by looking at how much power enrichment they have. I can't see it being lean at all without the injector table being set up wrong or a different maf and not having the correct table for it. Of course some kind of mechanical issue could cause it but that would be true of any engine. Mine is a little different also because it has an E85 kit and 60# Deatschwerks injectors.