how does CAI work?

[fried]

ok, so there are numerous threads about how to make CAI, whys its good rah rah rah...

i just wanted to know how it actually works? i know people say its good cos it make ur *car breathe better*, because it sucks in colder air, which is less dense and theres more oxygen or soemthing....

but how does it work? does it SUCK in air during acceleration? or does it jsut catch watever air flow into the pipe? or is it a constant sucking as long as the engine is on? or what?

[BLKCRX]

simple cold air = more power... the colder your intake temps the more power you will produce ... the colder the air supply away from engine bay heat the better the results, also piping size can effect flow differences / type of material can effect heat sock, thus effecting your intake temps.

Regards James

[luzinit]

ok, so what does a resonator in a stock car do? is it there to do more than just "reducing noise" ?

[fried]

so is it being sucked in whilst accelerating? or constantly being SUCKED into the intake? or jsut air thats passing into? or what?

[TODA AU]

Exactly that, as you've guessed the resonant chamber in the factory car is there to help reduce drive-by noise.

Regarding CAI's
On a well-tuned aftermarket ECU the difference in power is roughly 1 hp lost for every 4 deg C increase in intake temp above ambient.
When breathing from the engine bay on a 20deg C day, the intake temps can easily exceed 40deg C…
That’s 5hp down the toilet needlessly…
Though not a lot, it's a parasitic loss you can easily do without.
Plus, if you’re on a budget, every little bit counts…
Some OEM cars...
The DC5R being a good example, have very aggressive temperature compensation tables & pull quite a bit of timing out when they detect heated air, so the losses are greater than would occur with an alternative engine management system. Clearly this is done to assure the vehicle will pass the warranty period without claim.
Another point of note, worth mentioning is the increase in intake length afforded by the CAI is often beneficial in itself...
(Re: DC5 again)
Temperatures aside, most Honda's like a bit of intake length beyond the throttle with a good flowing filter... Large gains to low-end torque with no other changes are there for the taking without / or little sacrifice to top end power. Diameters play a part too...

What can be drawn from this is that SRI's really don't work that well in many applications.
(Regardless of how good they may sound)

Cheers

[TODA AU]

so is it being sucked in whilst accelerating? or constantly being SUCKED into the intake? or jsut air thats passing into? or what?

The CAI draws air from outside the engine compartment.
Generally it is air of ambient temperature. (That found outside the vehicle)
The amount of air drawn in is obviously dependant upon throttle position and rpm but aught always be cooler than the heated air available within the engine compartment.

[Tofu]

i don't know what i see is related to an open cold air intake application or not
but on two dyno sheets, one with a cai and one with stock air box, (these are the only thing that have been modified and everything else on the car is stock), one dyno graph shows a dip in hp around 4500rpm - 5500rpm
and the one with the stock air box, (althought not generating as much hp) there was no dip in hp around that rev range.

could it be possible that the stock air box actually retains some of the air in back up or something?..i would think that the open air filter has got to a point where there was no closely available air to be sucked in so hence the slight dip in the hp curve..?

this was witnessed on the same dc5

[TODA AU]

Getting a win win everywhere with no other changes isn't the easiest thing to do. Usually there are trade-offs somewhere in the rev range.
That said, proper tuning can eliminate most area's like that asuming the rest of your combination of parts is sound...