abrupt change in power output around 70deg

[SSpeed]

For some time now I've been plagued with a big shift in power at around 70deg. I've confirmed it in datalogging on the road and today I just confirmed it on the dyno. Datalogging on the road we've made changes to WGDC and confirmed it's essentially closed until boost comes on. It seemed to do nothing for shifting the curve.

 

Datalogging on the road, I see boost threshold drop about 700rpm at around 70deg. On the dyno that is confirmed with a 700rpm shift in the torque curve. At 76deg my peak torque is at 4500rpm, at 66deg it's at 3800rpm.

 

I've had so many people look at my tune and so far nothing has proved fruitful.

 

This is e85 with a BNR 16G on an '05 Legacy GT in Denver, Colorado. The LGT has 150k on the original engine and 50k on the turbo. The turbine housing has been replaced once already due to cracking. The thrust bearing is in great condition, but my turbine blades have move clearance from the housing than they should these days.

 

Don't get so caught up on the peak numbers, they are 1.24 and 1.23SAE corrected respectively. They are at 5600ft on a Dynojet.

 

However, they are the same dyno, same car, same parts, same tune, same dyno operator.

 

Dyno 1

Temp: 76deg

SAE: 1.24

HP: 361awhp

TQ: 391 ft lbs

Peak torque RPM: 4500

Difference between HP and Torque: 7%

 

 

Dyno 2 (same dyno, same car, same parts, same tune, same dyno operator)

Temp: 66deg

SAE: 1.23

HP: 373awhp

TQ: 444 ft lbs

Peak torque RPM: 3800

Difference between HP and Torque: 17%

Increase in uncorrected numbers from 76deg to 66deg: 47 ft lbs and 13 hp

 

 

The car has exhibited this behavior across multiple tuners and multiple tunes so I'm thinking it is something mechanical, I just can't wrap my head around what that could be or how abrupt the curve change is. I keep thinking I must be missing something in the tune as the change is not linear at all. You can imagine what losing or gaining 47 ft lbs must feel like with just a small change in temp.

 

The present tune was done at 85deg and the IAT compensation values were fine tuned to basically keep the car from overboosting all the time as my boot threshold dropped around 70deg.

 

Below are the Wastegate duty cycles, tuned at 85deg. Above 70deg my peak boost is at about 3800rpm, below 70deg it's closer to 3200rpm.

 

 

And then the WGDC IAT compensation, finetuned over months to keep it from overboosting constantly as I got around 70deg. Bear in mind, this is all ambient temp vs IAT.

 

 

Could this be mechanical? I just don't see how it would be so abrupt.

[relative4]

For some time now I've been plagued with a big shift in power at around 70deg. I've confirmed it in datalogging on the road and today I just confirmed it on the dyno. Datalogging on the road we've made changes to WGDC and confirmed it's essentially closed until boost comes on. It seemed to do nothing for shifting the curve.

 

Datalogging on the road, I see boost threshold drop about 700rpm at around 70deg. On the dyno that is confirmed with a 700rpm shift in the torque curve. At 76deg my peak torque is at 4500rpm, at 66deg it's at 3800rpm.

 

I've had so many people look at my tune and so far nothing has proved fruitful.

 

This is e85 with a BNR 16G on an '05 Legacy GT in Denver, Colorado. The LGT has 150k on the original engine and 50k on the turbo. The turbine housing has been replaced once already due to cracking. The thrust bearing is in great condition, but my turbine blades have move clearance from the housing than they should these days.

 

Don't get so caught up on the peak numbers, they are 1.24 and 1.23SAE corrected respectively. They are at 5600ft on a Dynojet.

 

However, they are the same dyno, same car, same parts, same tune, same dyno operator.

 

Dyno 1

Temp: 76deg

SAE: 1.24

HP: 361awhp

TQ: 391 ft lbs

Peak torque RPM: 4500

Difference between HP and Torque: 7%

 

 

Dyno 2 (same dyno, same car, same parts, same tune, same dyno operator)

Temp: 66deg

SAE: 1.23

HP: 373awhp

TQ: 444 ft lbs

Peak torque RPM: 3800

Difference between HP and Torque: 17%

Increase in uncorrected numbers from 76deg to 66deg: 47 ft lbs and 13 hp

 

 

The car has exhibited this behavior across multiple tuners and multiple tunes so I'm thinking it is something mechanical, I just can't wrap my head around what that could be or how abrupt the curve change is. I keep thinking I must be missing something in the tune as the change is not linear at all. You can imagine what losing or gaining 47 ft lbs must feel like with just a small change in temp.

 

The present tune was done at 85deg and the IAT compensation values were fine tuned to basically keep the car from overboosting all the time as my boot threshold dropped around 70deg.

 

Below are the Wastegate duty cycles, tuned at 85deg. Above 70deg my peak boost is at about 3800rpm, below 70deg it's closer to 3200rpm.

 

 

And then the WGDC IAT compensation, finetuned over months to keep it from overboosting constantly as I got around 70deg. Bear in mind, this is all ambient temp vs IAT.

 

 

Could this be mechanical? I just don't see how it would be so abrupt.

Does your fuel pressure increase at that temp?

[SSpeed]

Thanks for the question. Which tables are IAT compensation for fuel? I'm looking through and only see changes by load and timing.

 

FYI, I disconnected the ECU boost control and the problem still existed. It's either mechanical or in the tune, but not WGDC related.

[covertrussian]

What's your total timing looking like between the two temps? Do some data logs and compare timing. Make sure to log IAT's too.

 

Also take a look at your IAT Timing compensation tables.

[Cincy05LGT]

I've seen bad MAF sensors cause this.