Lost power with MAT sensor

[immortality]

Hi All,

spend some time tuning a VT XU6 on a dyno today. Car is fitted with 15psi pulley, 2 stacked mini MACE W2A cooler plates, 69mm TB and high ratio rockers with LS1 MAF.

Tuning using The1's VT SC enhanced tune

Car was making about 195rwkw still using the factory AIT sensor. I then switched over to the MAT sensor the owner had fitted and lost a considerable amount of power, adjusted the spark correction Vs IAT table to suit the MAT sensor but we are still 10rwkw down on the previous results.

After changing over to the MAT sensor we seemed to be getting less airflow?

I'll post up a couple off screen shots of the power runs shortly to show what I mean.

[immortality]

XU6 AIT sensor air flow.png (83.85 KiB) Viewed 5075 times

Actual AFR was about 11.8:1 (using the dyno facility WB O2), MAF is showing about 10100hz and continues to climb almost the full power run and cyl air is similar. Air temps are stable at 22° C.

We believe this car is possibly showing some false knock as it shows the same knock retard at the end of the pull regardless of total timing.

As above it made 195rwkw.

[immortality]

XU6 MAT sensor air flow.png (87.19 KiB) Viewed 5074 times

This is the last pull with the MAT sensor. MAF now plateaus at about 9400-9600hz from 4400rpm onwards? cyl air also reaches it max of 1077 mg and starts to drop from 4600rpm onwards, air temp post blower can be seen climbing to 70° C + and actual AFR's increased slightly to about 12:1(no changes made to fueling).

made 185rwkw like this, power is fairy consistent with previous runs till the point the cyl air tops out and starts to drop off.

Even the dyno operator seemed a bit confused by the drop in MAF readings but surmised the drop in cyl air may be an air density calculation issue based in the much higher air temps seen with the MAT sensor?

Any suggestions on what may be causing this and possible way to fix would be much appreciated. I'd rather use the MAT sensor as I'm told the owner of this vehicle gives it a hard time.

[immortality]

Dyno operator seemed fairly happy with the fuelling been about 12:1 but what do you guys suggest is most optimal?

Also not sure about what timing to aim for. Dyno operator doesn't have a lot of experience with these V6 engines.

[antus]

I have less experience with the MAF cars, but I think you might be hitting the limit of the MAF. cylair is based on MAF hz, so if you are sure more air is going in and the MAF hz isnt going up, you might want to try another MAF. Your not hitting the cylair limit which is 1650mg/s.

[Jayme]

the pull with MAT sensor in it, the advance at the end doesnt drop off as fast.... I would hazard a guess thats got more to do with it, its probably running too much advance near the end of the pull?

also the IAT sensor does play a part in the airflow calculation for the MAF. it should ideally be at the MAF. its not really supposed to be used to measure air temp post blower.... moving it into the manifold will stuff up some of those calculations, as your dyno operator said, its the hotter air appearing less dense and making it think there is less air going in. personally if I really wanted to go off MAT, I wouldnt hack one into a pcm designed for it to be in the intake at the MAF, I would move to a MAP based computer which is supposed to have it in the manifold and tune that actually I did that on my mates boosted ecotec the map sensors are much more predictable and controllable for me to tune

[immortality]

It is a shame we don't have a MAFless option for the ecotec/L67's. I think the owner may be considering A2A after seeing the air temps post blower.

Next time it goes on the dyno I will try it with the timing dropping off like the earlier runs.

[VL400]

Can you get a snapshot of the log with the markers on the same/similar RPM to compare fuel and spark?

The calculation is based on air mass, which should be measured by the MAF using its internally temp compensated circuitry. I dont think the IAT sensor has a huge effect on running in these systems? But then again I have not had a huge amount to do with them, I stick to MAP systems too

[Dylan]

Could $11P be a option for this set up?

[delcowizzid]

does it still run a boost solinoid its not limiting boost v's intake temp with the higher reading iat