BlackWorksInc
New member
Well the factory CAI is actually better than most aftermarket units in terms of performance (in terms of sound that's a subjective matter) and most people actually "downgrade" than upgrade with most CAI set-ups.
The factory air filter is good at what is does and there's no free lunch. Regardless of what their "internal testing" shows (why didn't they cite a 3rd party lab that peer-reviewed their results?) every vehicle I have seen with an Oiled Style filter has had a dirtier intake post filter to pre-throttle body and typically dirtier MAF (including some that failed due to very dirty Thermistors which lines up with K&N's testing). Which is in line with any "performance" filter, you give up filtration capability for "more air flow" which doesn't matter for stock engines.
The MAF is going to read the amount of air coming in and send that to the ECM; changing the filter isn't going to do much because the engine has been built to breathe a certain way from the factory. To get better volumetric efficiency (physical breathing ability of the engine) requires far more work than an exhaust and a filter can ever provide. Additionally tweaking the MAF readings just lies to the ECM and will run the vehicle either richer or leaner depending on what you're doing; tweak it too far and you'll set DTCs, so really you're not gaining much because any significantly worthwhile amount of change will cause the ECM to think there's an issue. Sure you might get a smidge more HP way at the top end, but you'll be running richer and dirtier; or you might be running leaner and getting a hair more MPG but then you're hotter and possibly burning stuff up.
There's plenty Toyota has done wrong and continues to do wrong, but when it comes to the factory CAI and the factory filter it's actually better than most aftermarket junk you can throw on there (though the hydrocarbon filter is weirdly stupid idea since it's non-serviceable and after 80~100k it can get a bit nasty). I think there's only a handful of quality CAI that improve on the factory set-up (Volant being one off the top of my head) but they're very pricey for what you get.
Post Note-
The "Dirty Intake" your talking about post throttle-body is thanks to the EPA and engine design progress, it's what you get when you go away from "Draft Tubes" and want more power out of a fuel injected vehicle running quality fuel. But it's also how you get an engine to perform better, not knock on good fuel, and meet emissions goals (the use of EGR helps a bit with knock reduction). You can add a "oil catch can" if you want, but you'll find the amount of oil to be minuscule compared to say an oil puking Prius or BMW. Most of that mess is less blow-by from the crankcase and more due to exhaust gases and unburned fuel flowing up the intake when the engine is in "valve overlap" of the intake/exhaust stroke.
Like I said, there's no free lunch unfortunately; you get more power and reliability out of the engine, but the intakes get a bit dirty (I'll be honest though, these 4.0L and 4.7L don't have much of any liquid oil in the manifolds like some of our other engines.)
Additional Note-
Man I didn't mean this to be such a lengthy post... [MENTION=89794]BackOff[/MENTION] I'm not trying to come across as though I am attacking/putting you down. I'm just trying to provide my experience and the results of research I've done into the matter. I personally don't recommend K&N or oiled style filters because of that and the cost/benefit of them, but they aren't going to destroy an engine if you run them (maybe dirty a MAF, but you can clean those).
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