COLD AIR INTAKE RANT:
In the late 1970s I saw a K&N display at a local 4x4 store. The display was a clear plexiglass box with a fan in it that blew air up a plexiglass tube about ten inches tall. When the K&N filter was inserted between the fan and the tube a ping pong ball floated easily in the middle of the tube, but if an OEM air filter was inserted the air flow got choked off and the ball fell to the bottom. The sign in front said “Let your engine breathe for better power and fuel economy!”
Below the K&N display there was a lengthy explanation of parasitic energy loss from the engine having to fight to suck against the resistance to get the air it needs. I’d used early K&N filters on my dirt bikes, mostly because everybody told me they would make more power, so I bought this line of reasoning hook, line, and sinker. As it turns out, that was all complete bullshit, but millions of dollars in marketing and race sponsorship has kept them swimming in money. (When you rebuild your engines after every race, and you’re being paid millions in sponsorship fees, you can afford to worry less about filter effectiveness.)
Years later the CAI — “cold air intake”— sales pitch was added… That said that cooler air from outside the engine compartment is denser, and therefore contains more oxygen by volume than the hot air under the hood, so the engine will make more power if it’s fed outside air. I bought that one too.
As it turns out, that’s 99% crap too. When I finally saw all the data I discovered I had spent thousands of dollars over almost twenty years installing various air filtration systems that did zero good (and some bad) for my trucks and jeeps.
My brother and I ran Powerstroke (me) and Cummins diesels (him) for more than 35 years, and we spent a lot of time and money on tuners, cold air intakes, bigger turbos, and other mods between about 1985 and 2008. Near the end of that time Ford, GM, and Cummins diesels were developing much more power from the factory, and the diesel forums were posting extensive research on mods. An engineer on one of those forums put together a comprehensive series of tests that measured rear wheel horsepower before and after the installation of various CAI options. He also measured filter efficacy, loading, and air flow by measuring initial resistance (with new filters), resistance after loading, and the size of particulates that passed through the filters when new and at various stages of loading. The power and economy loss to OEM filter resistance was, at best, negligible — and even when small improvements appeared, they weren’t repeated or sustained, as the filters loaded more quickly.
In summary, most aftermarket filters allowed larger particulates through, most quickly loaded to the point of greater-than-OEM restriction, most produced negligible if any improvement in power or fuel economy, and most produced more rapidly declining performance because of the rate of loading to much greater than factory resistance. That makes sense if you think about it, as all of the big auto manufacturers have the benefit of infinitely larger R&D budgets and all the automotive engineering equipment and talent money can buy. Ford or GM could buy or sell a K&N, Banks, or AFE with their couch change. If one of these little companies actually stumbled on a magic key to improved engine longevity, fuel economy, and horsepower GM or Ford would have bought them lock, stock, and barrel long ago. Now add Toyota, Volkswagon/Porsche, Honda, Mercedes, and all the other enormous vehicle manufacturing companies, several of which have been around more than 100 years, always trying to improve power and fuel economy.
K&N has been around 5+ decades, but consider the number of more recent arrivals that have magically outsmarted the entire automotive industry by designing better, simpler, solutions for cheap power and improved fuel economy… Again and again, small teams of poorly funded, poorly resourced, guys are designing better intake and filter solutions than the brilliant engineers at Ford, Subaru, Porsche, Cummins, Dodge, Mercedes, Toyota, Honda, Jaguar, Ferrari, and GM could design with 100,000 times the combined resources, facilities, time, talent, and R&D budgets. If that seems a little unlikely, it should.
As it turns out, the CAI game is about 98.5% hype too — and the tiny part that isn’t hype isn’t applicable to daily drivers.
The research I referenced got me about 90% of the way to overcoming my bias in favor of CAI, but my brother and I had been installing these on our trucks forever, so we decided to test the performance of our two trucks, a Ford F-350 Powerstroke and a Ram 3500 Cummins, with their cold air intake, and after reinstalling the factory air boxes and filters. I was convinced the performance of both would decline noticeably when we reinstalled the factory parts, and I thought they had, maybe because they were noticeably quieter without being able to hear the turbos spool (which I missed). Unfortunately, any performance change was within my margin of timing error. That was pretty discouraging for both of us, because we’d spent so much on these filters/systems over the years.
As to the value of the “cold air” in this context, the answer is near zero.
Significantly colder air is denser, so it does contain more oxygen by volume. That can make a significant difference at the drag strip, but the small temperature differential achieved by CAI systems has an insignificant effect on an engine with a turbo, as forced induction achieves a multiple of the density effect of the slightly cooler air.
The final nail in the free-flowing-intake argument came when the engineers did before and after dyno tests on engines with OEM filters and no filters at all. The dyno lines tracked on top of each other like they were traced.
The amount of air needed to optimize combustion efficiency/performance is well known to all of the big engine manufacturers. Even small independent race teams have had that nailed for decades. When massive amounts of fuel and boost are flowed to build massive power, more air is needed, but most of us aren’t doing that with our trucks, and the calculations I saw for the 7.3 Powerstroke, and 5.9 Cummins made it clear that the factory air filters wouldn’t be a limiting factor until somewhere well north of 500 hp which, at that time, was a long way off. Every modification package my brother and I built included cold air intake, but, as it turns out, it was the programmed fueling rate and boost that drove the diesel performance improvements. At the fueling rates were were actually burning, the CAI and 4-inch exhaust was irrelevant. More air flow than OEM filter would allow might have become necessary if we tried to push closer to 750 hp or more, but below 500 hp the factory filters and aftermarket clones (Fram) were fine, while protecting the engines better and requiring less frequent maintenance.
Do CAI make sense on our daily driver Trucks/jeeps/cars? Nope. Even if they bought another 20 horsepower, and they don’t, it just wouldn’t matter, and it definitely wouldn’t be worth the cost, maintenance hassle, or risk of larger particulate pass-through, but to show that I’m not above continuing to make stupid decisions, I installed the S&B CAI on my Jeep. I liked the hood scoops and I thought I’d enjoy the sound. I’ve seen zero improvement in performance or fuel economy, of course, but the sound makes me feelfaster! And now I’m stuck with regular maintenance, more expensive filters, and the inability to replace the filter with anything but S&B. I hope they stay in business…
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