2015 STI - first little up-grade
Discussion
Magic919 said:
How does that work?
Subaru STI's have always been very sensitive to changes, this one is no exception.CAIK's increase the volume of air going into the engine, this has a tendancy to exceed the limits of the MAF sensor which then cannot adjust enough to compensate, it means too much air in the fuel mix which leans it out, and that means the top quality cast pistons used in this fragile 2.5ltr engine suffer because of it. Its no doubt one of the reasons Subaru Japan wont authorise any performance mods on this model and why they only run them at 265ps in their domestic market cars.
Magic919 said:
The bit about the MAF 'adjusting enough' doesn't really follow. It just measures airflow and feeds that to the ECU. Maybe the MAF is pegged, but seems like a small change for that to occur.
Welcome to the world of Subaru 
14 years of experience of this marque, 3 STI's and a UK turbo, one of the reasons I didnt go for a 2.5 is the engine issues they suffer from, even forging them doesnt fix the problems, plus you get to understand what you can and cant do when modifying them, CAIK's need mapping, a panel filter doesnt, decatting needs mapping but changing the exhaust pre cat doesnt.
WRX's are more tolerant to mods due to not being as "highly strung" as STI versions.
stubbsey said:
Tony - if it was leaning out too much, wouldn't that show up via an engine management warning?
No, not necessarily, you would need something that specifically spotted a change in afr, the ECU is set up for a standard car so its designed to compensate for that, a caik lets far more air in than a panel filter so will struggle with it, hence you need a remap.stubbsey said:
No issues so far - and AEM don't suggest any other changes are required
my understanding is that this simple change shouldn't require a re-map.
if I changed the pipe from front to back and lost the cat then the stand ECU couldn't cope and a re-map would be required at that stage
I don't think it's a worry that the MAF can't read airflow at higher rates, it's that change to the inlet tract can mess with the calibration.my understanding is that this simple change shouldn't require a re-map.
if I changed the pipe from front to back and lost the cat then the stand ECU couldn't cope and a re-map would be required at that stage
In closed loop, the car will adjust to correct AFR (up to around 15%). So if you drive around gently for a few hundred miles and then read the AFR learning and it's only correcting by a few per cent, the intake kit hasn't thrown it out. If they're all stuck up around 15% then it's reached maximum correction and you're going to need a rescale on the MAF.
I removed the plenum chamber on my car for a while (because I wanted to run a duct through the wing rather than chasing any gains) and under logging it had quite a variable MAF reading for a fixed RPM/load/throttle - put it back in and all sorted. They can be fussy.
- I've not seen a 2015 management system yet, so this might have changed in some way*
- oh... I'm not a professional tuner either*
Good post Konan.
Ah yes, this is a common one.
Many modifications without a suitable remap have destroyed many Impreza engine's over the years never mind the 2.5 that is very fragile in comparison to the 2.0. I personally wouldn't risk it as a proper rebuild costs serious money.
I've always had the mods fitted and then the car has been immediately remapped before been driven.
My car has an Alcatek mapped by EngineTuner and its worth pointing out that a remap will make a very significant difference to your car in terms of the increase in power. I kept having issues with the MAF so in the end I elected for an Alcatek so I could go MAF'less.
Ah yes, this is a common one.
Many modifications without a suitable remap have destroyed many Impreza engine's over the years never mind the 2.5 that is very fragile in comparison to the 2.0. I personally wouldn't risk it as a proper rebuild costs serious money.
I've always had the mods fitted and then the car has been immediately remapped before been driven.
My car has an Alcatek mapped by EngineTuner and its worth pointing out that a remap will make a very significant difference to your car in terms of the increase in power. I kept having issues with the MAF so in the end I elected for an Alcatek so I could go MAF'less.
There's no real need for a change from the standard air box unless your going for big power, front mount, etc.
I've got a JDM Hawk running 400bhp on the standard air box with a Cosworth Panel Filter. The std box is good for up to 420sih bhp, after that it becomes restrictive - or so i was told.
I've got a JDM Hawk running 400bhp on the standard air box with a Cosworth Panel Filter. The std box is good for up to 420sih bhp, after that it becomes restrictive - or so i was told.
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