It's been discussed here before that changing to a cone filter will help lean out your engine. That statement isn't true because the MAF and the o2 sensor tell the computer to add more fuel to the engine counteracting the added air intake therefore giving you worse gas milage and more horses.

The only way would be to alter the map or change the readings.


Am I correct in this comment?

I ask because I have the cheap cone filter upgrade and got to thinking.

 

i think you are correct sir

 

the MAF does not read the same when you change the stock air box.

ie: go to a cone filter - the MAF thinks its taking in less air - so it leans out your fuel at some RPMs.

 

If you are getting WORSE gas mileage, you cant be getting MORE horses could you? Using more gas= running rich= LOWER hp??

 

No, point is the intake allows more air in.

more air = more oxygen. more oxygen = more gas that can be burned in each cylinder cycle. more gas burnt = more power.

 

More gas dumped in the cylinders, running "fat?" or "Pig Rich?"

 

Ok...
-So more air into the engine
-Computer dumps more fuel into cylinders to keep, what is thinks, is correct Air fuel ratio
-More power but still runs rich because of computer map telling it to do so.
-Less mpg
-More horses

That is why high hp. cars get bad gas mileage. Right?

So maybe I'll go back to stock to get more mpg. Hopefully factory reflash leaned out engine... Therefore more MPG. Good.

Thanks!

 

You guys are getting way ahead of yourselves.. Yes that theory is correct... But a simple cone filter Mod won't completely change the car like the way you guys are stating.. That comes down the road with big mods..

 

well actually the TBE with cone filter and no tune can do crazy things ...

 

It will lean it out a bit, but not much. Even if the computer dumps more fuel to compensate, it usually is not enough to bring the air/fuel ratio back to where it was before and a bit of power is made through a slightly leaner air/fuel ratio. Plus, there is less restriction with a high flow filter element and the turbo doesn't have to work as hard to pull the air in and compress it so that alone frees up some power through increased efficiency. You are correct though, in that to get the most dramatic results an ecu tune is necessary. Thankfully, ECUTEK has just been released.

 

The TBE is another subject entirely, reducing backpresure without telling the ECU raises boost pressures and the motor has absolutely no idea what's going on... Subarus do very bad things in these circumstances.

 

what do you mean with that?

 

Who brought scoobies into the conversation!? lol.

 

haha i know im lost with that

 

Well, I had an 04 sti for almost 4 years, and know quite a bit about them. You're misunderstanding why it causes a problem. It's not that the motor doesn't know what's going on, because the map sensor tells the ecu how much boost is being hit and the ecu will adjust timing tables and air/fuel tables to compensate. This really isn't a discussion for this thread or even this forum for that matter, but I'll go ahead and clear this up.

The reason that the STi tends to overboost with a turbo back exhaust and no tune is that the 2.5 liter pushes a lot of exhaust volume through that baby little VF39 turbo, and the tiny wastegate cant let out the excess exhaust gases fast enough to maintain boost targets without overshooting.

Porting the wastegate can alleviate this issue completely with no tune required, or if ecu tuning is desired then tuning the wastegate duty cycle mapping will allow the boost control solenoid to stay open longer to bleed off pressure that would otherwise be over taxing the wastegate. I hope that clears things up a bit. Now back on topic...