I was always under the impression that modifications to the 'dirty' side of the air intake system were legal. I did some searching and couldn't find a good link/explanation one way or the other though.

I did just pass with a deck plate (closed) at a pretty thorough smog place...

-Charlie

Seems the deckplate and ISR mods are both heralded and scorned, depending on the audience
Isr mod new info, must read!!!!!

If I find a decent airbox in a junkyard one day I might try the deckplate mod, but I like the idea of screening it to keep birds and boulders out, regardless.

A friend of mine had a dual headlamp goat that he converted to single hi/lo bulbs and ran intake scoops to the second headlight hole from a closed air filter housing.

The idea was MPH forced induction and lower intake air temp rather than breathing "hot" air from inside the engine bay. My seat of the pants dyno didn't register much difference.

With that picture, depending on the CFM of the carb used, it wouldn't make much of a difference, if any. The carb would be the bottleneck

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Carb and throttle body are bottleneck #1

Cam timing is bottleneck #2

Cylinder volume is bottleneck #3

Chamber volume is bottleneck #4

Chamber swirl and quench is bottleneck #5

Unless the engine's components/characteristics are designed to operate under certain conditions, changing a single parameter after the fact usually creates negligible results, or introduces new problems. In my experience.

Haha well, sure, if you wanted the long, more in depth, more accurate version.


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Haha, the devil is always in the details

All the chevy performance/hot rod mod mags went crazy over factory vortec heads when they first showed up on chevy trucks. BOLT ON 40 HP, they said. The frenzy at the junk yards was on, it was a blood bath.

But unless you had a dyno and were building with the intended design in mind (and had the right casting heads) you might as well have turned your ride into a pig. You need to use domed pistons and the set the quench pad just right with a shim gasket, plus California only has 91 octane. Run anything less than 9.1:1 compression or 93 octane and you'll eventually detonate yourself into a new engine with every pedal stab.

Similar with GT40 heads on 289/302 fords.The head flows great, but the chamber was actually higher volume than stock heads, so you lost compression. Can you say turd magnet? But put those same heads on a 351 Cleveland with flat tops, 1.7:1 roller rockers, an .030 gasket with a decent cam and you have a 400 HP (at the crank) motor on 89 octane.

Then one also needs to consider trans gear ratios and rear end gear/tire size to make a winning combo, but that's another story

Yeah, each smog tech is different. I was [un]lucky to get a veteran who knew the smog regulations and could literally quote them. He said that if the airbox had any cracks or openings it did not mention repairs, but "it must be replaced with a non-cracked or altered box". New airbox for me

There's plenty that also pass smog with the 7th injection and other "illegal" mods but I have not had such luck.

Resurrecting an old thread here. I’m currently running the stock intake with a k&n drop in. Sounds like a few people recommended not using one when running the deck plate mod and replacing it with a oem style filter instead. Any particular reason for this?

Since it's actually drawing in some air from the front of the vehicle at speed, it does collect a little bit more dust on the filter. But that's why you have a filter... don't listen to paranoid people and go enjoy it! You can always close the deckplate if it's that dusty.

I also have an oiled filter and the deckplate mod.

I have yet to do the deck plate mod... I still have it... just haven't done it...

but for the filters I will say this... I LOVE not having to worry about oil on my filter, 50% of the time, after a long dusty-dirty offroad, I can 'bang' lightly my filter and ALOT of dust comes out. IDK about you, but I'm sure the oil based filters can't clean most of that out cause it's sticking to the oil... I am running Toyota brand air filter (denso).

this is my opinion, you're entitled to disagree...

K&N's do have the lowest filtration rate among major filter manufacturers. It's hard to reproduce real world situations seen by a filter but there's been some good attemps that show this. So your point does have merit. It really depends on how you use your vehicle though. If you don't offroad much (I don't) or live in a wet climate where dust is not very common, it will not factor in as much as it would for a overlanding rig that sees dirt all the time.

I have an aFe oiled filter, which in the same test filtered out twice as many small particulate than a K&N. Still less than a paper filter but pretty darn close. I gained +9 peak HP from the filter alone though... so I'm sticking with it.

How/Where did you apply the mesh? I am considering doing the same.

You can hot glue mesh to the inside of the fitting.

Just don't forget to close it in heavy rain or when fording streams.

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gotcha! I'll grab some next time I'm at the hardware store. My problem is going to be remembering to cover during the rain. Thanks for the info!

Good info here:
Toyota 4Runner Highlander Deckplate and Air Filter Modification