Help me understand my log

[twg]

I have 04 USDM Forester XT, buy engine is essentially stage 2 STI (with vf39, sti tmic...etc)

Couple of things:

1) MAF sensor tells me the amount of volume of air coming into the intake independent of anything else right ? Does that mean that if in 3rd gear, 5000rpm, at 15.8 psi, if MAF is 250g/s, and in 4th gear at 5000 rpm at 16.8psi, also showing 250g/s, means that the power is the same at both cases ? And does this mean that in 4th gear, I'm essentially blowing hot air, since despite an extra psi in boost, I'm still getting the same MAF reading ?

2) My fuel trim #3 (long term fuel trim right ?) is showing -45 to -55, does this mean my car is running REALLY rich ? Which maps do I need to change to adjust this ?

3) My car's ecu is tuned for 91 octaine.. but I have 94 octane here.. boost seems to be max'ed out at 18psi on a vf39, so I don't want to go higher, but what else can I change to make more power, and take advantage of the 94 octane... advance timing ?

4) Lastly, is there an easy way to tell from my logs whether I have an intake leak or not ?

[twg]

anyone ?

[twg]

anyone ?

[moxie]

I have 04 USDM Forester XT, buy engine is essentially stage 2 STI (with vf39, sti tmic...etc)

Couple of things:

1) MAF sensor tells me the amount of volume of air coming into the intake independent of anything else right ? Does that mean that if in 3rd gear, 5000rpm, at 15.8 psi, if MAF is 250g/s, and in 4th gear at 5000 rpm at 16.8psi, also showing 250g/s, means that the power is the same at both cases ? And does this mean that in 4th gear, I'm essentially blowing hot air, since despite an extra psi in boost, I'm still getting the same MAF reading ?

Well the motor functions independent of gearing so it should be making similar power at similar rpm regardless of the gear you are in once it is loaded enought to spool the turbo.

Its possible you are going a little out of the efficiency range of the turbo.
I did think that you could run VF39 over 16-17 psi with no big problems.

2) My fuel trim #3 (long term fuel trim right ?) is showing -45 to -55, does this mean my car is running REALLY rich ? Which maps do I need to change to adjust this ?

Can you post the log?
I would like to see it to have a better idea.

3) My car's ecu is tuned for 91 octaine.. but I have 94 octane here.. boost seems to be max'ed out at 18psi on a vf39, so I don't want to go higher, but what else can I change to make more power, and take advantage of the 94 octane... advance timing ?

I would not recommend tuning timing unless you are going to be on a dyno. The only useful and safe way to tune timing is on a dyno. You need to be able to see the reaction of the motor to the changes you are making, so just blanket raising timing can get you into trouble.

Personally I would run the 94 with my 91 tune and just be happy i have that extra detonation protection barrier. I run a mix of 91 and 109 at the track, and i only really do it for the benefit of the motor when it is being run long and hard.

You are probably leaving less than 5-10hp on the table, so it might not be worth the effort if you dont have access to a dyno.

4) Lastly, is there an easy way to tell from my logs whether I have an intake leak or not ?

Could look at your A/F Ratio, if it is always lean you could have a leak after the MAF letting in unmetered air.

What are your Abs Pressure readings at idle?

[twg]

I've attached the log...

The reason why I suspect a boost leak is because I've seen STIs MAF sensor go to 260g/s max... whereas mine only hits 250 and seems to stop there...

I also hear a bit of a whistling sound at WOT... lastly, the red hose from the sti Y pipe to the turbo inlet, there's a small tear, don't think it's a complete tear but not sure if it's leaking either... if there's an easier way to check with the logs, it's better, as it's a PITA to remove the sti tmic and put it back...

[Freon]

1) MAF sensor tells me the amount of volume of air coming into the intake independent of anything else right ?

Correct. It is measuring the mass air flow. The amount (mass) of air traveling past the sensor location over a given amount of time. Generally lbs/min or g/s. It should be representative of what is traveling through the engine as well, as long as you don't have any leaks or a vented to atmosphere blow-off valve.

Does that mean that if in 3rd gear, 5000rpm, at 15.8 psi, if MAF is 250g/s, and in 4th gear at 5000 rpm at 16.8psi, also showing 250g/s, means that the power is the same at both cases ?

Not really, but you have a good general idea. AFR, engine efficiency, and ignition timing play a role here, but yes, your power is going to be closely related to the amount of air you are pumping through the engine. That's the largest factor.

And does this mean that in 4th gear, I'm essentially blowing hot air, since despite an extra psi in boost, I'm still getting the same MAF reading ?

Possibly. At the same RPM, same airflow, higher boost may mean that it is just warmer air. I'm not sure I'd be that concerned. I wouldn't call that conclusive.

2) My fuel trim #3 (long term fuel trim right ?) is showing -45 to -55, does this mean my car is running REALLY rich ? Which maps do I need to change to adjust this ?

I don't know if that is an extreme number or not, but I think the thing you really need to watch is injector scaling and MAF scaling. Is is always -45 to -55, or does it move around a lot? If it is steady, but low, injector scaling would probably be smart. If it jumps around a lot in value, you may want to compare MAF voltage to airflow and fuel trim. If at a certain MAF voltage you are always reading rich or lean, you may want to adjust the MAF scaling at that point.

You should average out to about zero (injector scaling), and not jump around too much (MAF scaling, physical factors, sensor life, etc).

3) My car's ecu is tuned for 91 octaine.. but I have 94 octane here.. boost seems to be max'ed out at 18psi on a vf39, so I don't want to go higher, but what else can I change to make more power, and take advantage of the 94 octane... advance timing ?

You may be able to bump up timing slightly, maybe run slightly leaner as well, but neither is a big factor. That's impressive to run that much boost on 91 on a VF39. How is your timing and knock?

4) Lastly, is there an easy way to tell from my logs whether I have an intake leak or not ?

It depends on where the leak is. Fuel trim, comparing boost to airflow and AFR may show problems.

[Freon]

Looking at your log file, your car seems pretty happy. It's running plenty of timing even on boost, good knock correction values, injectors not maxed, etc. I didn't finger through that whole thing, but did a quick glance at the high throttle runs.

[twg]

Hi... thanks for the comments...

the only concern I have is that the fuel trim #3 is at -44 to -50... and it's pretty constant... I'm going to get dyno'd with AF soon so that'll tell me whether I'm rich or not..

I'm not sure what fuel trim #1 is... that seems to be closer to 0...

If I'm running rich, then looks like there's still power to be had...