Cold air intake

Are there any benefits to a cold air intake with a washable type high flow filter element? I don’t mean the hype pushed by the seller . . . any serious benefits? Rocketman

I think only at wide-open throttle, any other time it should make no difference, power or mpg-wise.

More intake noise, if you like that.

Depending on the car, a CAI can give you improved performance off the line because it draws cool air rather than heat soaked air from under the hood. Some cars are designed so that heat soak is not an issue. Note that if you have a shiny metal CAI, it will warm up to underhood temperatures and heat the cold air before it gets to the throttle body. The best CAI’s are usually home-built ones made out of CPVC pipe.

Oh, and regarding washable filters, I’m not a huge fan. The oil gets on the airflow sensors, and tests have shown that they don’t trap as much dust as a good paper filter.

This issue is more complicated than it appears. Shadow has made some excellent points about aluminum tubing rapidly transferring the heat from under the hood to the incoming intake air. In addition, any CAI system that is drawing air from the same cavity as the OEM snorkle (most do) isn’tt rellay giving you cooler air at all.

Also, I’ve seen in some CAI systems changes in the location of the mass airflow sensor. And all of them change the airstream environment that the MAF sensor is designed to read, meaning a poorly designed system could result in operating problems.

IMHO the only thing these boxed CAI systems do is take your money and reduce flow restriction. And the oiled filters can and in some cases do coat the sensing portion of the MAF sensor.

Don’t “buy” the hype. If you want cold air to enter your intake, find a way to get it. In my case I

  1. opened the false “ram scoop” in the lower front bumper and added a grill, actually supplying cold air.
  2. created a “plastic chamber” behind the scoop with pieces of plastic cut from a storage container and mounting tape
  3. removed the OEM air intake snorkle and replaced it with a 2-1/2" shop vac hose and a 1-1/2" shop vac hose, both taking air from behind and above the new air inlet scoop.
  4. removed the carbon filter from my airbox’s topp half to reduce restriction.
  5. and lastly, I insulated the induction system with heat barrier/insulation (from the parts store).

I now have real cold air from outside, coming in under increased pressure when on the highway, coming through (an) intake(s) totalling a 93% increase in capacity, and kept cool by insulation. And it no longer has to go through that rediculous carbon filter.

Note: before I did this, I did some research.
I calculated the maximum total amount of air that my naturally-aspirated engine can draw in. That’s the total displacement of the engine divided by 4 and multiplied by the redline rpm, 6200, then multiplied by 70% to factor in adjustment for the valve cycle. For a 4-banger with a 180 degree crank that gives me a good guesstimate.
I then looked up my injectors (380cc) and determined if my injectors had excess capability to maintain the ideal 14.8:1 air/fuel ratio before reaching saturation.
I then researched as best I could the flow capabilities of my stock air filter, to see if I’d be maxing that out.

I also added velocity cones cut from plastic toot horns (like from the football games). Bernoulli’s princilples work in plastoc too.

The whole thing worked…beautifully. Definite power increase on the highway. I lost 2 mpg when driving aggressively, but remember that the energy is in the gasoline, not the air. Mileage on the highway with the cruise control on remains that same as always.

My system does what CAI systems claim to do but don’t. And it does it with the stock air filter. Think about what you’re actually trying to acomplish. Don’t just buy something on a guess or a sales pitch.

My total cost:
2-1/2" hose: $25
1-1/2" hose: $15
mounting tape: $6
Plastic storage bin $8
Toot horns: $4

" air intake with a washable type high flow filter element?" I suggest you only touch those with that 10 foot pole you have in the garage.

Those oiled filters can be OK (minimal gain) if you are very careful with oiling that filter.

Cold air intake? Where is your air box pulling its air from now? I am not familiar with every car made, but from what I have seen, manufacturers stopped pulling underhood air and have ducted in cold air from the front of the car since the 1970s.

Passenger cars have air boxes designed to muffle intake noise, which can be slightly restrictive at high RPM, but I assure you that if the manufacturers found that a different intake design would get them even 1/10 of a mpg, they would redesign the intake. Nothing you can do will improve highway performance.

I have seen air intakes in every conceivable location, and the only places that work are well above the hood (where it blocks your vision, like you see on dragsters) or at the base of the windshield facing rearward, used by GM in the late 1960s. Don’t try replicating that unless you are prepared to re-design your whole fuel injection system.

As noted by others, oiled reusable filters let in no more air, but let in more dirt, even if you keep them properly oiled, which no one ever does. If I am used car shopping and I see an oiled cloth air filter, I walk away.

I would add to Manolito’s comments that air intakes that start with velocity horns immediately behind the grill or behind a front opening also work, they’re called “ram air” intakes. Because they’re dependant on the speed you’re going, they do nothing off the line, but do work at speed.

He and everyone else is right about oiled filters. Your intake system is designed to allow sufficient air to be drawn in by your cylinders, subject to restrictions intended to muffle sound and/or reduce emissions (like that carbon filter I had in my airbox). Improvements can in some cases be accomplished but at the cost of sound and/or mileage. Most OEM injectors in an OEM system have some margin before they become maxed-out (saturated), so reducing restriction and adding a bit of intake pressure voa ram air can help. Pumping in air with a turbocharger or supercharger will saturate the injectors and require larger injectors and remapping of the ECU. In short, these oiled filters do nothing useful and can cause problems. Any gains at all accomplished by the boxed CAI systems come from reducing restrictions, and they’re extremely minimal, not worth the risk.

the same mountainbike wrote: “the total displacement of the engine divided by 4”

Shouldn’t that be divided by 2, since there’s an intake stroke every 2 revolutions of the crank?

Nope. In a 4-banger with a 180 degree crank, there’s one cylinder on the intake stroke at every revolution. Since the total displacement is the total of all four cylinders, the amount being drawn in at any given time ends up being total displacement divided by 4.

I almost made the same error the fist time I thought through the problem, until I realized that there’d always be one cylinder (and only one) pulling air.

“there’s one cylinder on the intake stroke at every revolution”

There’s an intake stroke at each half revolution.
There are two pistons going up to TDC and two going down to BDC at any given time, one going down on intake and one going down on power.


At each half-revolution you’ll have one cylinder on the intake stroke, one on the power stroke, one on the compression strike, and one on the exhaust stroke. Next half-revolution, the one that was previously on the exhaust stroke will be on the intake stroke. The one that just finished the intake stroke will be on the compression stroke. There will constantly be one cylinder drawing in air.

I tried to find an animation but was unsuccessful.

“At each half-revolution you’ll have one cylinder on the intake stroke”

So that’s two intakes per revolution.
You’re saying the same thing as me, except:
It’s the total displacement of the engine divided by 2, not 4, regardless of the number of cylinders.

At any given time at any point in the crankshaft revolution there will be one cylinder drawing in air. This animation ain’t great, but I couldn’t find a better one. You’ll notice as you run the animation that there is always one cylinder on the intake stroke.

I know someone who took a car that would do 0-60 in 7.5 sec from the factory, added a cold air intake now it does 0-60 in 9.5 seconds. Would you call that an improvement?

There are a lot of baffles in the stock system to smooth out resonant spikes that are not in the cold air systems. The cold air system may improve hp at a specific RPM, but it can be detrimental across the RPM band.

MB, not being nearly as smart about this as you, I tend to agree with almost everything you say. This time, though, after thinking about it, Circuitsmith is right.

(assuming the standard 1-3-4-2 firing order) If 1 is on it’s intake, 3 is on it’s exhaust. When 1 fires, 3 will start to intake. You’ve just completed 1 full revolution, with 2 intakes. Wait, are we all just saying the same thing?

3 will be on its compression, 4 will be on its power and 2 will be on exhaust.

Chassios, did you view the animation? It includes labels above each cylinder that change between intake, compression, combustion, and axhaust strokes as the stick-figure crank rotates.

I have to admit, however, that it’s hard to envision. I too stumbled on it at first.

Keith, you’ve made an excellent point that the effect can be different than expected. These things don’t always work as advertised. But sometimes, when they don’t, one can learn from the adventure.

Unfortunately, I can’t get to that site from work, so no, I can’t watch that particular animation until tonight. I’ll watch it later. Unless the animation uses something other than a standard 180 degree crank, though…bear with me here, while I think out loud…

4 stroke cycle… 1 down, 2 up, 3 down, 4 up…intake, compression, power, exhaust.
2 crank revolutions per cylinder.
2 pistons firing per revolution.
4 cylinders, all 4 firing in two revolutions.
4 intakes, compressions, powers, exhausts per two revolutions.
2 intakes, compressions, powers, exhausts per revolution.

Unless everything I ever learned about the 4 cylinder, 4 cycle motor is wrong, that should all be correct.

I will admit, form this point forward, I know nothing about cold air intakes, and have never seen the benefit of modifying the intake plenum too much for the amount of money and aftermarket system costs, and then only get that measly improvement at a very limited RPM range. I can’t keep the motor in that range with only a 5 speed, so it just always seemed pointless to me. So there…I kept the thread on track. (sorta) :slight_smile: