Adding An Automotive Cold Air Intake

[Thomas] and a buddy were sucking down a few brews when they decided to hack their 2001 Chevy Cavalier for a bit better performance. If they could find a way to bring cooler air to the engine they speculated that they’d see an increase in efficiency. Instead of routing the air intake to a hood scoop, they took off the factory air filter and mounted a cold air filter in its place. PVC pipes were then used to create a delivery path from the front of the vehicle with the output in close proximity to the new filter. They tested their work and discovered a drop in intake temperature from 101 to 48 degrees Fahrenheit at 60 mph, and from 109 to 54 degrees Fahrenheit at 45 mph. Now the sedan runs better and generates more horsepower, all for around $35 in parts.

118 thoughts on “Adding An Automotive Cold Air Intake

  1. Yeah I’m with Bob on this one…

    I’d imagine that the turbulence that PVC creates in the intake voids all gain from the temp drop. But maybe not considering the PVC isn’t attached to the intake. Difficult to tell without actually putting the car on a dyno, or the intake on a flow bench.

  2. when i did CAI i wasnt checking on my milage, but it sounded good.

    required parts
    – 2002 ford focus zx3 w/ 2.0 zetec engine
    -fiberoptic protective tube(1.5in thick)
    tools: drill, cable tie.
    actions: drll a hole in the resonator, guide tube to lower grille, ziptie at grille, plug tube into hole in resonator.

  3. Bunch of morrons, this is nothing to do with temperature. It’s only becase of their air filter is one of those sporty-high speed air intake.

    Because it has less resistance to the air flow, it goes through the valves faster. With more air, more power to the pedal.

    Too bas for them this thing will increase noise, quicker valve wear, higher oil vapor inside the engine.
    Just let them think they are great, I dont care. ^^

    1. You’re an idiot. It’s all about air temperature. ALL that matters is the amount of oxygen available for combustion. Colder air is more dense, therefore more oxygen vs. warm air in a given volume.

  4. Not true deadeye. Air density changes greatly with air temp. Going from 100 degrees to 50 will net you roughly 10% air per volume. The engine will have no problem delivering the extra 10% in fuel. If they took the time to dyno it, they should see just shy of 10% in hp gains. Next time you accuse someone of being morons, make sure it’s true. Just sayin’.

  5. Yeah it’s one thing to criticize, but there’s no need to get all hostile over something like this…relax if you don’t think it’s a good idea say so, but don’t call them morons for trying something out.

  6. @Deadeye

    Not so fast. Colder air = more dense air thus more air molecules per given volume (volume is of course static). More air molecules = more fuel (pcm adjusts fuel in relation to total air MASS) and bingo, more power.

  7. Easy @deadeye, they probably did see some modest performance gains. Any MAF based system will register the higher air density and respond accordingly.

    My worry with the intake mounted low like that is the possibility of the engine taking a big gulp of water and hydro-locking. More likely hydro-exploding, watch out for puddles.

  8. I see nothing special about this at all. I wouldn’t even call it a hack since building one of these is extremely easy, and done every day for performance gains. It’s actually one of the first mods import car guys usually do.

    There is no increased wear on the engine, aside from choosing a less effective filter. Cone filters are not less effective than a normal square filter, but a k&n filter does filter less effectively than a paper filter. The benefit is that it flows more air than a paper filter.

    All this mod has done is make the intake flow more air at a colder temperature. Definitely a good mod if you’re looking for a minimal gain in power, but there are much better ways to do it.

    The correct way is to use mandrel bent aluminium pipe and an intermediate foam filter. That way when you hit a puddle you suck air through the foam filter instead of sucking water up your intake and into your motor.

  9. Then again, it is a Cavalier. Maybe they are trying to hydrolock the engine? I do have to worry a bit about how the PVC will hold up over time, but for pocket change you can rebuild it every year if you need to.

  10. Cold air is better. Cooling it reduces its volume so it can pack more air molecules into the cylinders and reduce the engine’s likelihood of detonation. There used to be an aftermarket kit for the M3 like that. It destroyed more than one or two cars because it would pick up the h2o from the ground spray and suck water into the engine. We used to call them puddle suckers.

  11. Alex M is correct.
    We have been using cold air intakes on our custom builds for years and the dyno results suggest an increase in horsepower, amongst better throttle response. Cold air is especially on forced induction and turbocharged systems.

  12. I am with everyone else. This is the first mod teenage ricers do to their hondas. We were doing this back in the late 90s for christ sake. Come on HAD I miss the old days.

  13. im sorry but i have to say this is not something i ever hope to see on had again.

    yes its a good mod, all it is is a pvc air scoop that throws fresh (cooler) air into the engine bay, which in turn has more cooler air available. but to say its a Cold Air Intake is misleading, and to post this up as a ‘hack’ is very discouraging… what will the next automotive hack be, a hacked-off exhaust being listed as ‘high flow’ ?

    i just never expected to see the same home depot cavalier mods that clutter up the rest of the net here on had…

  14. Was gonna comment earlier but now I have more points to make

    So the mod wasn’t the new filter, but the PVC redirecting air flow, right? It’s not clear through the few pictures. Dyno test won’t prove anything – this is a ghetto ram air setup so it relies on the wind coming at the car.

    Who knows maybe it increases drag enough to hurt the mileage.

    Everyone around here, myself included, used to do this to our cars when we were like 16.

    The next step up is that you can trick the car’s computer into thinking the intake air is colder by replacing the sensor with a resistor of the appropriate value, thereby making the engine run rich. I actually had a potentiometer hooked up way back when. Good ol’ days :P

  15. For all the “it’ll suck water” people. I’d agree if the filter was directly attached to the pipe. As I see it, if the pipe got any water in the bottom then the engine will just pull air from the rest of the engine compartment. If the bottom was pointing straight out the front, then maybe, but probably not this setup.

  16. This is a pretty interesting hack.

    I’d be careful if anyone gets the idea that since a little more is better, a lot more should be fantastic. Many modern engines are often made up of multiple metals (usually an aluminum head with a cast iron block). Metals expand at a different rate based upon their temperature which is one of the reasons a thermostat keeps the engine at a specific temperature. Another big reason for the operating temperature is for the oil. The viscosity of oil changes with temperature. You don’t want the oil to cool too much or friction will increase, the engine will have lower output and a have lower lifespan as you put the block/head through a lot of mechanical torture.

    Just be mindful of these things if anyone decides to try to hack together something crazy like a liquid nitrogen chiller for the air intake in their car just to see how far they can push it. It’s not like overclocking a computer. Screw it up and you may end up walking. ;)

  17. if you’re making the the pipe running to the intake longer, you’re making it harder for the engine to breath, ie breath in, then try breathing throw a straw, join two straws together, its hard to suck the air in as it gets longer. an na engine is working on atmospheric pressure so its sucking in air as fast as the inlets allow it, in order to equalise out.

    If a CAI works, its because the old system wasn’t working properly in the first place, especially on an NA engine.

    Usually it just makes it louder, and that makes the butt dyno think its going faster.

  18. I’m a hot rodder at heart and use the tech information out here to cobble together a data logger / traction control, but leave the mechanical engine tweaks and ideas to the website specifically for them… Please don’t post a Home-Depot air spliter next…

  19. @sam

    they actually do have systems to cool the air charge even more. CO2 systems that spray the intercooler fins on turbo cars to cool the intake charge even more are available as kits already. There are nitrous kits that do something similar as well. Colder, denser air is always better than hot air. period. It will always produce the most horspower because a colder air charge equals more air and fuel in the combustion chamber.

  20. I did this to my zx2 when I was a kid with dryer hose and a K&N filter (I put a screen over the intake for bug protection though) and actually saw slightly better mileage.

    This is the most common car hack around, and if you spend some time on it there is definitely a return investment of some sort.

  21. Wouldn’t it have been better if they used aluminum or some better material that would cool the air a little more? I also think that if they were going to go through that much work they should have done a Ram air / cold air intake for a little extra!!!

  22. Note that you can also hook a pot up to your maf sensor to trick the computer into thinking you have colder air than is actually coming in to get a richer fuel mixture, although it’s kinda stupid to do it if you don’t know dick.

  23. It don’t even think this is a cold air intake, its more like a vent to the engine compartment. It just directs air towards the air filter, the stock airbox on my toyota truck is more cold air than this, as it pulls air from inside the fender, instead of inside the engine compartment. I don’t think this could even suck water into the airfilter, its not even sealed, to create a vacuum, that would suck enough water to hydrolock it, from a 3 inch or so pipe its not even directly connected to, seems impossible. Unless I didn’t see all the pictures.

  24. colder air doesn’t always automatically mean more power, its the potential to make more power, power usually comes from spark advance. certainly any noticeable power over whats already going to be a close mix.

    the intake manifold is really hot especially at a power level where altering the amount of o2/fuel would even begin to do anything, taking in a slightly cooler charge ends up being even less slightly cooler by the time its gets to the combustion chamber. If the existing setup is pulling hot air in from the engine thats causes it to be significantly higher by the time it reaches the chamber, thats one thing, thats rare, measure the IAT on almost any car at WOT and you’ll see how fast it ramps up.

    the ecu runs the car for a given intake temperature at X spark and Y AFR, if its not optimium, it takes it away.

    cooler is better, but lengthing pipes, and getting air thats maybe only slightly cooler another.

    i’m sure people imagine some massively different explosion going on in the combustion chamber because the air intake is maybe slightly cooler.

    Calculate the change in air density and how much of a temperature change you’d need for a typical chamber vs how much extra fuel is added.

    maf’s measure air flow not density. tmaf’s measure temperature and airflow, if you tell a maf its flowing less air than you actually are, it could be all sorts of bad, you end up in the deceleration area of the maps and run nowhere near enough fuel and too much timing.

  25. my CAI did improve my mileage. Not much, but it did help. It gave me 1 mpg on the low end (city) and about 2mpg on the top end (hwy). Now this is on an 88 Grand Marquis (not great gas mileage to begin with). To top it all off, mine is one of those dryer hose “Home Depot” specials. I did use a K&N Apollo as the filter since I wanted a completely enclosed system.

    yeah, I use myspace to host my blog… it’s free.

    Mine did cost well more than $35 though. The Apollo I found for about $120 and the rest was Home Depot parts and duck tape. I did have to saw the washer/coolant tank in half (left the washer half where it sat) to allow the hose out the front of the car and got an aftermarket tank at a local parts store for $10.

  26. people have been doing this shit for years. that’s not meant to be a negative comment, it’s good that a DIY cold air intake is finally in the HaD archives now. for more PVC fun, try mounting a potato gun on a jeep. ok thats a dumb idea because how you supposed to load it? but automate the loading process (beyond me), automate the filling of combustion chamber(much simpler), then wire the ignitor to the car horn switch :D
    now forget that i ever suggested such a destructive idea..

  27. I’ve got a K&N intake on my truck, and whenever we have a cold snap, I have a really hard time not peeling out everywhere. No need for PVC in my case, the kit creates a little compartment in the corner opposite the battery that’s shielded from the rest of the engine compartment, and it gets plenty of air directly from around the headlight.

    Speaking of air from around the headlights, this concept is really old- they did a much better job in 1964…

  28. I have no hard numbers, other than the dyno sheet my K&N came with, and the rest of the engine is stock, so it doesn’t maximize any ability to suck more air. But I do know, it hardly costs anything to clean it, compared to buying a new filter, so I’m more likely to keep a clean filter in it, which is better all around for performance both power and efficiency.

  29. I bought a machined aluminum Cold Air Intake from Matrix about 5 years ago for my ’95 Civic EX(VTEC).

    $50 for the intake, $15 for the high-flow air filter. Made a world of difference and I don’t have to worry about PVC melting all over my valve cover for only $35 more.

    There is a reason they don’t use PVC plumbing pipe for engine components, you know. There are specially made plastics and composites designed for high temperature and high-stress applications like in a car’s engine compartment.

  30. @PhilKll- good point- I try to clean mine before every trip. If I don’t, I usually drop 1 or 2 MPG. I also put on headers, high flow cats and y-pipe, and a high flow cat-back. I went with a single instead of double as I wanted performance, not noise. Then I added 10.4mm race wires, irridium plugs and a DiabloSport Predator tuner. I did it a while ago, so I need to upgrade the tuner so I can get custom programs via e-mail by sending data logging files to someone who does custom programs.

    The best increase in efficiency, though, was changing my driving habbits. I increased my gas mileage by 20% by keeping it under 70, dropping 10 MPH from the bottom of hills to the top, and accelerating very gently.

  31. “The best increase in efficiency, though, was changing my driving habbits. I increased my gas mileage by 20% by keeping it under 70, dropping 10 MPH from the bottom of hills to the top, and accelerating very gently.”

    Yeah, that does make a huge difference, learning how to use the gas pedal properly. Kind of like learning to use the brakes properly, they last a lot longer with nice smooth stops, instead of last second ones.

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