De restiction of air box

[wardy]

Does anyone know if derestricting your air box is illegal? Or what are the rules with reguards to your induction system.

[mr_astra_retired]

I doubt it would be illegal .
As long as the filter is enclosed you should be fine. If you get pulled over i dont think the cop will want to look inside your air box to see if its de-restricted , if you got a pod , different story .

[blackSRi]

Yeah, just removing an internal pipe doesn't change the fact the filter is still enclosed in the box, so no dramas, but then again, I'm not a lawyer!

[RapidSRi]

technically if the work does not have an engineers report its not legit, but probablity of anyone noticing would be .001% I was pulled over with a pod whirring in my Mazda and they didn't even notice it cos the car was standard looking.

[Benny-o]

I'm really not sure how de-restricting your air box is going to make any improvements at all.. I keep reading these posts and i still don't get it. I guess i need pics to show me wat is actually goign on but i doubt you're going to get any performance increase by removing an internal pipe in ur air box as ...

a) You're not changing the diameter of the inlet or outlet pipe, so no more air is coming in or going out, it'll stay the same.

b) The air still flows the same path, removing a couple of inches off the pipe isn't going to increase air flow, it's still getting drawn from the same point on the other side of the filter..

I just don't see it, the ppl who have done it are assured that it increases performance but i'm thinking it's really more of a placebo effect..

There was a post the other day about dyno results, only diff mod between 2 cars (after exhaust) was a k&n filter, which made something like .5kw difference i think??

I dunno watever moves your furniture i spose. (not having a go at anyone either, just to be clear)

[~Kupu~]

There was a post the other day about dyno results, only diff mod between 2 cars (after exhaust) was a k&n filter, which made something like .5kw difference i think??

I dunno watever moves your furniture i spose. (not having a go at anyone either, just to be clear)

that was actually between wardy and boosted astra and it was .1kw......

[BoostedAstra]

Benny-o

What u talk about is mine and wardys car. i got .1 more with a stock filter over his k&n. Both have had the mod to the air box, it does make a difference, have a look at the inside of an airbox and you will understand

BA

[Benny-o]

Fair enough, i'll have to have a looksi, might do that this arvo. Just still find it hard to believe you're going to get better air flow or more air flow when you're not changing the size of anything that's all. That and the engineers designed the air box the way it was, surely they had a reason, (or didn't have one to see reason to remove the pipe) puzzle's me a bit.. but anyway always good to see mods that work!

Which reminds me to post a follow up to that dyno result, by those results i'm estimating that SRi N/A 's pull about 93FWKW.. keen to see..

[Degen-Astra]

Ever so slight I would say but...an advantage is an advantage.

From my understanding and also doing this as well, you actually do allow more air through because both the inlet and outlet on the air box taiper down to a smaller diameter than that of the actual induction pipe itself.

By removing this you do let some more air into the motor quicker, even if it is slight. The only problem is that air running from the airbox to the motor will actually be MORE turbulant than stock. Due to you having removed the bellmouth that helps to direct air more effectively into the direction of the motor.

When I had my 1.8 i was going to have a bellmouth fabricated to insert into the aribox to reduce this turbulance, but I didnt end up getting around to it. Maybe when I can be bothered to do it on the 2.2 I will see the difference then.

[BoostedAstra]

As Nick said, in regards to the actual piping I always thought it was just to muffle the intake noise a bit due to sound dampening. could be wrong but...

BA

[woody]

I was under the impression that the airbox was designed to deflect and then spread the incoming air across the entire air filter. The greater area for filtering will reduce resistance you will find and also the better the wear on the airfilter.

Has anyone derestriced the airbox and later re-instpected the filter? Did you find one area was the primary point for catching the crap coming into your engine?

I don't profess to know the fluid dynamics of the airbox but think about it this way...

put a piece of tinfoil over an icecream tub - get a hose - turn it on and point it directly at the tinfoil... it's gonna make a hole right?

but it you deflect the water off another surface first you decrease the immediate impact pressure and the tinfoil will.. well it's tinfoil so it will probably still break!! but you get my point! the pressure is less and the water will cover the majority of the tinfoil

it's the old performance over longevity debate...

Is it worth a .1 kw increase to have to replace your airfilter more frequently??

[blackSRi]

I took my airbox hose out 1+1/2 years ago to see what would happen and I found that the car drove smoother when RPM was upped especially changing up gears and climbing hills.

Other changes, air incoming noise was louder, and my filter isn't dirty in one spot (standard factory filter replaced only at standard services).
I put the hose back in a couple of months ago and I could feel the difference when I put my foot down driving up the steep hill from my house (I drive up the same hill every day to work for the past 2 1/2 years), so I took it out again.
As for dyno, never popped the car on the rollers so I don't know but foot down, changing up and up hill it feels better (smoother - esp 1st to 2nd and 2nd to 3rd). A mate of mine who has a WRX agreed the car felt better under acceleration.

I didn't do it for power - if that was the reason I would've put in a K&N, but for a smoother drive (the engine always felt like it wasn't breathing well b4 the change).

Anyway, the reason the intake pipe is in is probably for fuel efficiency/flow over the filter or noise reduction.

[16vopl]

dont forget to reset the ecu after you change the intake, i think your sposed to do it on the calibras and should be the same for all cars?

the engine is getting more air and needs to re-adjust to suit.

[Anonymous]

How long is a Piece of String?
Why does Earth Orbit the Sun, But Yet The Moon Orbits Earth?
Questions that will be asked for a Eternity.

It doesn't make much or any power gains, It makes Throttle response Quicker.
I have done it to my 2.2, Driven it hard. Replaced the Bellmouth, Drivin it hard.
Made pretty much a Bees Penis Difference in Performance.

Thats my Opinion.
Flame on :lol:

[YuSuF]

Spot on KID :wink:

[mr_astra_retired]

y bother doing it

Better throttle respone , plain and simple