Going Leaner As RPMS Increase

[TAPyvehc93]

I'm working on getting my WOT MAF dialed in but I'm having some issues getting the AFRs more stable and closer to target. The setup is a turbo 5.3 on 14lbs or so, E80%, boost reference fuel pressure regulator and a MSD boost a pump. From what I can tell from the logs, when the truck grabs the next gear during a pull the boost seems to go up a half pound or so and as it climbs rpm, the boost decreases slightly. Could this be the reason why its going leaner at the top of the gear? If you noticed it starts off around low 11's (gas scale) and by the top of the gear its hitting 11.8, all while being in the same MAF hertz. Also, why am I seeing a minimal MAF hertz increase from say 9lbs of boost to 14lbs of boost? ......hpl

[SUTTERERMAN85]

Is your fuel pressure dropping?

[lukearmstrong1990]

my opinion from combo and the data.

your MAF isn't changing much because the turbo is flowing a similar amount of air past the MAF (pre throttle body) in the cooler pipe throughout the RPM increase. your boost is measured inside the manifold. so air flowing past the MAF is at a different pressure and density to the air in the inlet manifold.

boost is only a resistance to flow. your boost pressure decrease (logged from inlet manifold data) is likely being caused by a lack of flow through the turbine housing past the turbine wheel and out the dump pipe. as RPM increases it generates a relatively increasing volume of burnt, expanded gas that needs to go through the manifolds and turbine to escape. more RPM more exhaust gas. your turbine wheel, housing and manifold likely cant flow that volume so it chokes up loading the turbine wheel slowing the turbo down. that is why you see a minor boost pressure drop as RPM increases. if the turbine and exhaust side chokes up bad enough it will build enough pressure in the manifolds to physically push open the wastegate to get out.

small turbine combo is responsive, builds boost fast and has excellent mid range. downside it wont flow the volume of exhaust gases created at the higher RPM efficiently. big turbine combo can be lazy to come on unless combined with an auto a matched high stall converter. but they will flow the exhaust gases efficiently at high RPM and if its efficient enough it ill get increasing power with RPM.

however pre throttle body where your MAF is the air flowing past has little dynamic change, hence the constant MAF data. I believe your AFR creep is caused by the IAT increase and the consequential fueling adjustments made by the PCM. if you wish to fix your AFR fluctuation I think the IAT fueling compensators would be the best spot. as far as the MAF is concerned the air is very similar through out the RPM and MAP changes.

that's why I personally tune all turbo cars in SD

[TAPyvehc93]

Is your fuel pressure dropping?

I'm actually not logging it at the moment because my fuel pressure gauge goes to my aero force gauges which run off the OBDII so when I'm logging with hp tuners I can not read it. I am however pretty confident that its not a fuel pump issue or anything like that.

[TAPyvehc93]

I was actually thinking going SD would be my best bet. I'v been thinking about it for a while now. As far as the turbo goes, its a 75/75 on a 5.3 with a 3" downpipe to a 4" exhaust. I was under the impression that I have room to grow. Are you referring to the flow rate multiplier vs IAT? If so, thats all set to 1.00 so it shouldn't be changing it as the IATS go up.

[lukearmstrong1990]

a lot of guys from the US don't see my point of view as theyre attached to their MAF meters. I tune every boosted LS in SD. even if its a centrifugal blower on 5psi ill tune it in SD.

what are the specs of

turbine wheel
housing flange size (assume T4)
turbine A/R
manifold pipe size
crossover pipe size.


is there cats in the exhaust?

I was referring to cylinder charge temp bias.

[TAPyvehc93]

Also, is going speed density as easy as just failing the MAF in the tune?

[lukearmstrong1990]

apply 2 bar OS. fit 2 bar sensor. scale sensor. populate VE tables with data.

then just the standard MAF fail and DTC procedure. then write entire

[TAPyvehc93]

My VVE already goes up to 210 KPA and I can change the colum/row to increase the RPMs or the KPA range if needed. I also already have a 3 bar map installed and scaled. Do I still need to apply a new OS or should I already have it?

[lukearmstrong1990]

you can disable the MAF and use the VVE. it will work but it will only reference the low octane spark table. it can be a little glitchy but it works.

you can also set the dynamic disable/re-enable RPM values to maximum. this will make the PCM reference the VVE table only for fueling.

bear in mind the VVE is basically a calculator. making changes to the VVE actually makes multiple changes to multiple tables that we cant see. it uses the VVE values in an algorithm to calibrate many many tables to control fueling. the VVE is more or less there to make it simple for us who aren't IT engineers. it allows normal people to edit a strategy that would be too hard to teach how to edit nor create any understanding/sense from it.


applying 2Bar OS re-writes the entire OS giving an actual VE table that directly controls inj PW.

[TAPyvehc93]

you can disable the MAF and use the VVE. it will work but it will only reference the low octane spark table. it can be a little glitchy but it works.

you can also set the dynamic disable/re-enable RPM values to maximum. this will make the PCM reference the VVE table only for fueling.

bear in mind the VVE is basically a calculator. making changes to the VVE actually makes multiple changes to multiple tables that we cant see. it uses the VVE values in an algorithm to calibrate many many tables to control fueling. the VVE is more or less there to make it simple for us who aren't IT engineers. it allows normal people to edit a strategy that would be too hard to teach how to edit nor create any understanding/sense from it.


applying 2Bar OS re-writes the entire OS giving an actual VE table that directly controls inj PW.

I don't think I have the option to go to a SD OS on my pcm. The only options I see under the OS table is the speed density air mode and a few other "patches". So I guess tuning the VVE is my only option?

[lukearmstrong1990]

I believe so yes