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.

117 thoughts on “Adding An Automotive Cold Air Intake

  1. Turabaka,

    I did not claim otherwise. The performance will improve, that wasn’t in question.

    >Colder, denser air is always better than hot air. period.

    And not all engines can handle that. NOS kits are an excellent example of what not to do with stock engines, they simply aren’t built to take it.

    You’re talking about performance parts built to run on performance engines that are designed to handle them. I am talking about ordinary people trying to hack their stock cars for more performance. There’s a BIG difference between the two. Which do you think there are more of on Hack a Day? (Hint: This isn’t a performance auto forum.)

    Someone who is serious about performance automotive work will meet others who know what they’re doing (when they go to buy the parts) and save them from costly mistakes. Someone who tries to bypass the parts market altogether and hack something together because they heard about it on the internet doesn’t have the benefit of that experience.

    Go back and carefully re-read what I said… or not. Mod the family car without understanding the ramifications of what you’re doing at your own peril. I honestly don’t care. I won’t be the one spending a few thousand replacing an engine trying to prove someone on the internet that I know better than they do.

  2. @tbase I’m not saying that there are not gains to be had, but your problem with peeling out in cold weather probably has more to do with cold tar and cold tires than it does with the minor gains that you get from a less restrictive air filter.

  3. Good idea but I do agree with Turabaka there is a real danger of hydro-lock without a secondary form filter. AEM produces a Air Bypass Valve to eliminate the chance of your car hydro-locking if the filter were to be submerged. This is a good quick and dirty hack, although I would make an effort to add a secondary foam filter like AEM Air Bypass Valve to this build.

  4. @sexiewasd
    i was just about to post this. rubber stiffens in a cold environment, resulting in less grip.

    you get a squeal regardless of whether the loss of grip is from your souped-up engine or simply from the result of cold rubber :)

  5. Not sure why this is on hackaday. This is the most basic of basic modifications car guys do. I’ll be impressed when they pull off an LNF engine swap. Or turbo that 2.2 engine reliably. Or crack the ECU and remap the air/fuel binaries. This is as much a “hack” as changing spark plugs. Give me a break.

  6. CAI’s like this have been in use already for a while. This is nothing new, nor is this even remotely innovative. It’s the first mod most of us even do. They used PVC, which is alright, but more of a pain than using something like actual purpose-built, flexible, smooth-walled intake tubing.

    To those of you saying it’ll suck up rocks, bugs, water, etc.: Nope! The fender-well on most cars, such as these J-Body cars, or W-Bodies, and other unibody cars tend to be empty, but walled off from the environment. This creates pockets of cool, dry, relatively clean air. The only risk you take with a CAI that low is sucking in water if you try to enter a 6″ or deeper puddle. At that point, you’re flooding your interior. Or cracking an exhaust pipe. Or destroying the packs of glass in your muffler(s). Or worse.

    And to the nay-sayers of the performance improvements: It works. Short-ram intakes are those stupid filters you see that remain open under the hood. This sucks in hot air, decreasing the volumetric efficiency of your engine. These fender-well intakes take in air that’s 15-20 degrees cooler than what’s under your hood. Because of the CAI’s generally better flow, the air also is delivered from the cool location to the engine quicker, without picking up as much temperature. The drop in temperature increases the amount of air available to the engine. The ECU compensates for the newly created lean condition by adding fuel. The increased amount of air and fuel in the engine creates more power. You can gain even more power and efficiency from this simple modification with an ACTUAL HACK by cracking your Air/Fuel/Spark Timing tables and adjusting them to better suit your higher amount of air flow.

    Still not sure why this is here on Hackaday… it’s not really a hack. Look at those guys who cram LSx V8’s into cars like the Solstice or Fiero! The wiring, electronic control, and mechanical nightmare that would undoubtedly ensue would SURELY be a better hack than this…

  7. To further M4CGYV3R’s point, PVC has a tendency to harden and breakdown at higher temperatures, letting off potentially dangerous fumes. I’ve yet to see proof of anyone getting hurt by this, but PVC in the engine bay is generally frowned upon.

  8. This is the trashiest CAI I have ever seen. Also kind of hilarious that I tried to talk with the guys here at Hackaday about the free speed density conversion for 1g DSM’s ( btw) and they just ignored it… but they’ll post this air flow nightmare. Please people do not put plumbing parts on your car. It is not your bathroom sink. Literally you would have picked up more power just replacing the air filter with a velocity stack and leaving it in it’s stock location (provided it’s a speed density system).

  9. :S Seems like a lot of people didn’t read the article(errr looked at the photobucket). The pipe just guides cold air into the engine compartment. It’s not connected to the air filter. So there is no chance of sucking up water, etc.

    That said, I put a K&N filter in my car a while back, but I went with a stock sized one and kept my airbox. I don’t see how the short ram is beneficial, it’s so close to the engine it’ll just pull in hot air. In my ’97 intrepid the air box pulls air from the fender, so it’s nice and cold already. What I would like is to be able to increase the amount of air it can draw from the fender, I think that’s where more gains are to be had, is having less restrictive flow.

    So I might just have to try, but with a dryer hose…Since the general consensus is PVC is a poor choice.

  10. If what you’re after is efficiency — measured in increased MPG, then cooling the air is exactly wrong. Modern cars run hot on purpose. The engines are tuned to run hot and best burn the least total fuel.

    If bringing in cooler air could increase MPG (efficiency) at least one of the actual engineers at GM just may have considered something as inexpensive as ducting the air from a cooler place.

    If, on the other hand, you’re looking to improve the speed at which your car moves — the solution is to sell the GM Econobox, and buy something meant to be driven by someone other than an old mane with a hat.

  11. Fuel efficiency in MPG will decrease since there is more air to burn more fuel. Volumetric efficiency can increase significantly to produce a cleaner burn, with enough air to counter most factory ECU’s running engines pretty rich. Lowering the velocity of the intake air will decrease both efficiencies, due to the increased length of the intake pipe, which increases the friction the air must overcome and possibly choking the engine when it rains.

    A MAF system will benefit more than a MAP system, but still if you are going to modify the intake you should at least use an AFC (now you’re adding $100 easily) and set maps or at least thresholds.

    The PVC is probably the worst choice, the relative roughness is going to lead to turbulence which will negate any temp difference of the air at the outermost edge of the intake. Isolating the part of the intake still in the bay from the hot engine is going to net you with greater results.

    Finally, the best way to claim that lower temp air leads to greater power is to have it stay at low temperature in the intake manifold, mixed. This is the most difficult to achieve, but if it can be done (alcohol produces such high horsepower because the fuel keeps the charge at a low temp) then it is more of a significant step than any intake mods that are done.

  12. No doubt modest performance where realized, as this is a time honored hot rodding mod. But by the seat of the pants data gathering is relative,and should be taken with a grain of salt. As always this could be refined, but if the car owner is happy, that’s all that matters isn’t?

  13. I have done similar things to my Rabbit and Rabbit GTi

    I used a (heavily cut up) 3″ elbow and JB weld at the stock airbox connected to a Plymouth Voyager phenolic intake tube, with a funnel from Kragens zip-tied to the end. Routed cool air from the passenger side of the radiator. I think it picked up some power at night in the cold.

    Either way you look at it, it is worth checking your stock intake tube/airbox to make sure a bunch of rodents haven’t made a nest in it ;)

  14. Wow, I took a look at this picture, this guy seriously needs to lose that last 90° bend and put a shield around that cone filter to get the engine bay heat away.

    Any decent cone air system has a custom heat sheild so you don’t lose power due to heat-soak under the hood.

    Simple works too, get a rubbermaid box and cut out the sides that lead to cold air.

    Most hot rodders would simply move the battery to the trunk and remove that headlight (or stealth mod it with a tube going through an unused high-beam area, or even divert some air that direction with a simple metal flap placed behind the grille).

    Good for a first attempt hack though, but he didn’t spend much time thinking about how real cold-air systems are designed, or how flow works.

  15. There’s some seriously poor knowledge masquerading as detailed knowledge in this comments thread. It’s no wonder myths and misnomers about car tuning are rife on the internet.

    And all of that adds to the fact that, as mentioned, this is a bog standard schoolkid mod to help with a botched filter arrangement. No filter should be open in the engine bay in the first place, that’s the most ridiculous arrangement and I see it day after day as a “performance mod”. Filters, unless placed in front of the rads, in a well considered location, should be in a housing and fed from a cold location. Most stock boxes already do this, at least in european/japanese vehicles, and do this very well. Have any of you actually measured the pressure drop and intake temps across a stock intake setup – they’re actually pretty damn good on most cars. Usually the best solution possible, without completely re-building the intake, is to simply go for a lesser-filtering panel (K&N etc) to replace the stock one and lag the pipework.

    So many people assume that stock=compromise, or aftermarket=automatically better, without ever checking to see. The number of people I’ve had to break the news to about how their £100 “induction kit” is actually robbing them of hp (over stock) and then seen it proved on the rollers is quite frightening. I’m not saying stock is always good, or that stock will deal with a seriously modified engine, but at relatively lowly modification, the stock intake usually VERY well thought out and a team of very smart designers with CFD packages have optimised it to suit the engine, unlike the guys who’ll sell you a metre of stainless pipe and a sponge in a strainer.

  16. How cute, people who think they know about cars… CAI’s are a favorite of the honda wannabe kids. Unless your car is horribly designed by idiots a CAI will not help you. Just like how a K&N filter wont help you, or any miracles in a bottle, or any special sparkplugs….

    Hack a day is not the place to find REAL automotive information. Go find a website where real people are doing real stuff to their cars.

  17. I don’t know why a lot of people think this will improve gas mileage. Even with colder air, the engine will be still be pulling air mass in at the same rate for a given power output. The car’s computer will keep the air mass to fuel mass ratio where it should be, and the same amount of fuel will be burned.

  18. I’d be a lot happier if Hackaday had posted Megasquirt or something similar for a car performance mod. I’d rather see some home tuning on a handmade ECU than someone taking 20 minutes to drill a hole in the fender and place a piece of PVC through. I considered doing this to my car but the performance gains weren’t worth it, the most you get at the wheels is 2-3 horsepower with only an intake mod because you’re still restricted by your exhaust backpressure in most cases. The air system on the car was designed to meet the demands of the engine, without remapping the ecu you won’t see any real significant gains. It’s like most automotive mods, they only work well with tuning and with other performance parts. And in response to the person who posted the hydrolock protection kit, do you think they’re going to spend 200 bucks on something AEM if they refused to buy an actual CAI? I doubt it

  19. Weak, on last years’ BABE rally our comrades in team epic fail were having tons of trouble getting their poor Toyota around the mountain roads. We ended up all stopping together to check out why the car was struggling horribly to discover…

    There was no air box. NONE no filters no box just a fitting with a few bolts sticking out of it where the motor was sucking in air, to top it off she was sucking hot air from right off the transmission!

    Thus ensued a massive cross team effort to empty any plastic bottles in our possessions, cut the tops and bottoms, down the length. some kind of horrible elbow fitting was fashioned, and an aluminum duct tape, plastic, and regular duct tape amalgamation took shape. We found a source of cool(er) air from the fender (likely where the stock air box was sucking from). still no air filter, I think somebody suggested putting a stocking over something..? We tactfully ignored the gravel-sucking design and nothing happened.

    Team epic fail had no further problems with the motor bogging down, the new intake took them from the mountains of TN to NO in the middle of the summer. THAT is a hack.

  20. I’ve done a lot of testing of these things, and found that sucking the air that close to the ground serves no purpose whatsoever. Once you remove the OEM black pipe that spends too much time routing towards the intake, and go to just a shorter intake (even if it sucks air from the middle of the engine bay), you’ll get the gains.

    Your idling air temp will be up a bit, but once you start cruising, within a second or two, the air you’re sucking in drops to the ambient temperature outside.

  21. “Your idling air temp will be up a bit, but once you start cruising, within a second or two, the air you’re sucking in drops to the ambient temperature outside.”

    Not in my several years of testing, and if it does your radiators are massively larger than required, but I suppose that depends on your airflow arrangements under the bonnet. In most situations you’ll be getting air from the coolant rad, which will be in the region of ambient+30C or so. The OEM pipe is generally perfectly good unless your car was designed by an idiot, and often are shared with the much higher powered variants of the same engine, so more than capable. Your gains from a shorter intake are rarely large enough to compensate for the losses of warmer intake temps, despite what the aftermarket industry will tell you. Sometimes you can place the filter inside the bay but directly behind a large frontal opening that isnt fed by through the rad, which is reasonable, but it still should be boxed in as at any speed where airflow is not appreciable you’re running on hot air.

    Such as here (this setup is proven to reduce power with hot underbonnet temps):
    this is the proper way:

    Hackaday really isn’t the place for discussing car mods and thermodynamics.

  22. Though ultimately the best way to achieve cheap LARGE performance gains is to reduce weight, anyone serious about performance will head initially down that route to improve handling, stopping and going, before needing to add 5hp through intake mods.

  23. @ whoever said to use an AFC up there:

    That is the most special needs hack of a pos excuse for a tuning device ever. Did you consider what it does to your ignition timing when the ecu is running in a different load cell because the afc LIED to it? I hope some of you geniuses put AFC’s on your cars because you’ll be the guys I’m spanking using only a stock turbo and a real tuning system.

  24. I did this years back on my 04 Scion xB. How ever I found that using couplings caused too much air turbulence in the system and had a dip in high end. So I made one by heating and flexing the pipe to make the bends. Went even further to add same cross sectional area but yet pinched corners. It’s a trick they use in super high end exhaust systems.

  25. @James

    “Hackaday really isn’t the place for discussing car mods and thermodynamics.”

    I’ve always been disappointed by the lack of ECU and vehicle control systems (how about ABS, traction control, and stability control?) hacking. Sure, there are plenty of commercially available products for ECU tuning, but I haven’t seen many hacks.

    I guess the consequences of damaging an ECU or power train (expensive and inconvenient) and possible safety issues (think runaway Toyotas) make this kind of hacking a little beyond Hack A Dayers.

  26. How to increase performance of a Cavalier:

    * Take one(1) Chevy Cavalier
    * Open hood, doors, trunk
    * Remove everything of value
    * Sell said valuables on eBay
    * Use money to buy a Corvette
    * Place Cavalier badge in glove box of said Corvette

    (Note, humour, my wife had a Cav way-back-when, so no offense meant… but I stand by my accusation! :) )

  27. While this isn’t a ” hack ” this is a great idea! I’ve done this way back in the day and there are noticeable gains. Since the air is colder the molecules cram together ( more air same space ) add fuel and in this case spark = more performance. This is a tried and trued method, look up performance CAI and you’ll see run after run on dynos of people with CAI and without. Chances are with this one, the guy is just running the PVC up to the filter box and not all the way to the engine…I hope not… there the temps exceed safe temps for PVC, PVC is good for burst and cold…not for hot…it lets off gasses that will kill

  28. I’ve modded a few cars and been on other forums dedicated to this.

    The consensus is that PVC/Duct CAIs don’t work. And guess what, neither do K&N filters.

    You can get a high flow MAF and modify the ECM programming. This might give you some measurable gains. You’re better off ripping out your AC system than doing this.

    Most cars now are not limited by restricted airflow. Ditching your catalytic converters and a high flow exhaust would gain you HP in the double digits not double decimals.

  29. “Yeah, I’m going to have to go ahead and, yeah, disagree with you there.”

    In theory the ECM is going to compensate for the air flow (map sensor) and temperature (intake air temp) and adjust the air/fuel ratio based on these conditions. I would expect the gain to be marginal if measurable at all. Speaking of which, where’s the A/B dyno test?

  30. First of all, does everyone not see how absolutely BRILLIANT it was to post this pre teen caveman setup? Just look at the number of comments! Those are all site hits! Marketing GENIUS! Hats off to ya hackaday webmaster!
    Also OMG did someone say they need to take that 90 degree bend out of it? WTF.
    Where did YOU go to geometry class, Juarez?
    Thats clearly more like 20-25 degrees…
    But the airflow inside of that pipe Im telling you is AWFULL. Theres a reason ppl dont do crap like that and thats because inside that coupling theyres a sort of interior flange due to the fitting sliding OVER the pipes. On one inside surface if you could get your hand in there you would feel a huge U shape and that goes all the way around the interior circumfrence. Now you see just ONE flat surface inconsistency would cause what you would say ‘turbulence’. That is why Port Matching is done.(google port matching)
    When you have this square ravine on the ENTIRE inerior surface, at a BEND POINT no less, than the choke point you are creating goes way way beyond turbulence. Blissful ignorance?

    Also whats with the aftermarket cold air system sitting right there in the background?
    Am I the only one seeing this?

  31. Lowering the intake temperature yields lower efficiency because the fuel charge then burns at a lower temperature.

    Efficiency of the engine, when other variables are removed, is determined by the average temperature in the cylider during power stroke, relative to the temperature of the ambient air around the exhaust. That is, the hotter your intake temperature is, the less fuel you need to use to make the mass of air hot. This is why things like microturbines or stirling engines use pre-heaters for the intake air. A good heat recuperator can double the efficiency of the engine by recycling lost exhaust heat back into the combustion chamber.

    Internal combustion engines use intercoolers and generally avoid pre-heating to improve volumetric efficiency, that is, how much air you can cram in the cylinder. It would be theoretically possible to increase the efficiency through pre-heating the air – a turbo does this to some extent – but heat it too much and you’ll burn a hole in the piston.

  32. That is good at autumn or spring temperatures but it’s no good at Christmas time. And how will the engine start in August. The air’s not dry and the engine would be too cold.

    It’s a good idea with future potential.

  33. Hi. Please, how about some math to figure the length of PVC per engine size? I believe this gives a better mod(Hack?), I’ve read something along the lines of 1 inch of pipe length per CC engine size. Obviously taking into account the diameter of the carb. Is this not how one calculates a Ram Air intake? Some maths on this would help. Length of pipe also has something to do with, Where in the power band, the improvement occurs. I think short pipe for low rev range and long pipe for higher. Googling doesn’t throw up much, especially if you don’t know how to ask. Air flow in is at most pressure at the front most point of the vehicle in question. I feel some bonnet scoops are in the wrong place, due to aero dynamics. What do you think?

    Cheers Mike

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