Originally Posted by goNads
the larger the intake diameter the leaner it runs, yes?
I honestly can't answer this directly. Despite what you may read about your car not learning at WOT, it does. Every run I did with an aftermarket intake, the air/fuel ratio got richer and richer. Even after disconnecting the ECU after I did two runs and reconnecting it to do another two runs with the same intake. It seemed the ECU took up where it left off before and continued to make the car run richer, in all gears.
Also, different Subaru ECUs work differently. I noticed through dyno testing that an Impreza ECU the same year as mine just made a little later runs leaner. It's as if the ECU mapping is different. While my ECU keeps adjusting richer and richer until above 5000rpm, the air/fuel ratio can drop as low as 10.0:1, the one made later on the same year as mine won't go below 12.5:1.
I haven't gone about trying to figure it out. I just understand that this is the way it works.
In short, I'm trying to say that different intakes are going to work differently on different cars (even of the same make/model and year). Even your modifications will determine how rich/lean it's going to run. Each one will be a case by case test. I know my car just dumps a load of fuel above 5000rpm on everything except for the stock setup after it gets used to an aftermarket intake.
Originally Posted by chip4761
I think that greater hp gains are realized with the engine mods on this car. If you just slap on an intake, it's not going to make much of a difference. However, the catback has to help things out. Also, if you added some headers, I'm sure the intake would be working to its fullest potential. It seems like anything that helps the engine on the exhaling end would make the intake that much more efficient.
Is there a reason why this reasoning wouldn't apply to the stock intake as well?
I'm an idiot so I'm sorry if it's a simple explanation. Someone else said the exact same thing on another forum where I posted this up. I never heard anyone say this about the Cobb intake.