I've been fooling around with the intake system on my 2000 V6 and plotting a DIY WAI (yep, you read that right--
warm air intake).
I've noticed that there are basically
four holes after the air filter that one has to worry about. Two of them are simple vacuum type lines--a tiny hose and a medium hose on the air filter box top (before the MAF sensor), then the MAF sensor, and the PCV breather hose.
The small hoses are for engine control components, the names and purposes I can't remember off the top of my head. The point is those two hoses need a clean air supply. Fine, easy enough.
The PCV hose is also a simple clean air supply. Also quite simple.
The hard one is the MAF sensor hole. It has to be just the right size and shape, and the MAF sensor has to be secured by two screws. This part can't be fabbed, or if you prefer, isn't worth the time & effort to fab.
I've noticed a couple of peculiarities with the intake system that aren't addressed by the aftermarket intake makers.
#1 It seems that in aftermarket systems, the PCV breather is upstream of the MAF sensor. That's bad juju. The PCV breather tube can flow in reverse when there is blowby and the PCV valve is closed. The amount of oil mist that makes it through is probably tiny, but as the motor wears, there will eventually be a significant amount. The MAF sensor is an extremely delicate instrument. I would not spend $100+ on a system that could inject crankcase gases into the airstream before the MAF sensor.
#2 This one is long and complicated so bear with me. After reading extensively about the ACIS (see this thread:
http://www.toyotanation.com/forum/t45066.html) I learned about Helmholtz resonance and how all major engine manufs. utilize it to optimize A/F delivery. Feel free to wikipedia/google it, it's interesting stuff.
The resonator in the intake tract is exactly opposite the breather line. The shape and position of the holes in the plastic piece which incorporates the resonator made me realize that Toyota is using Helmholtz resonance as part of the PCV system. Perhaps this design reduces oil fouling due to blowby. Perhaps it accelerates the air into the crankcase. Perhaps the resonance frequency there matches the resonance frequency in the airbox. In any case, it's no coincidence that the large circular hole for the resonator is exactly opposite the small circular hole for the crankcase breather.
When I combine those two things what I get is "uh oh."
I've always understood that resonators in the intake system are to reduce intake noise. Well, I fabbed a short custom intake tract out of 2.5" conduit and ran it with the stock airbox. Basically stock intake tract except for smooth tubing in place of the resonator and the rubber boots slid almost all the way up & over the ends, minimizing the amount of rubber corrugation in the intake tract. I took the car for a spin and...no appreciable difference in sound nor power.
So I guess the sound effect is achieved with the removal of the resonator in the fenderwell. The resonator in the engine bay serves a different purpose. Another contributing factor to the noise equation might be those corrugated rubber boots. I could not find any boots of the same size so I simply used the stock ones with the conduit inserted as far as possible into them so the ends were almost flush with the TB and the AB sides.
So really what I am left with is sticking with the stock system and simply removing everything before the stock airbox. The intake will basically be sitting near a hole in the fenderwell. It will probably still mostly suck from the fenderwell but maybe a little from the engine bay also. It may be possible to fab up a little air redirector or something but that's about it.
The only other mod I see as being possibly worthwhile is lining the stock corrugated boots with conduit so that the inner surface is smooth. Maybe that will help maintain laminar flow in the intake. I know that turbulence in the intake manifold and head are crucial to efficient combustion. I wonder if maybe smoothing the airflow to the TB would actually be counterproductive. I mean, the smooth style rubber connectors are probably the same price as the corrugated kind. Perhaps the accordion style allows more flex? Perhaps there's a way to increase performance by placing vortex generators in the intake tract?
Anyway the most disturbing thing to me is the breather tube being upstream of the MAF sensor with no special consideration to reducing reverse flow in the breather tube. Other than convenience, why would they do that?
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