Which performance upgrade gives the best bang for the buck? This often asked question is impossible to answer definitively, but over the last several years, cold-air intake systems have comfortably nestled themselves near the top of most "best buy" lists.
Cold-air intake systems have grown quite popular in the aftermarket. Not only do the systems allow substantially more cfm of airflow than stock, they draw air from outside the engine compartment, which is much cooler than the under-hood air sucked into a typical conical filter upgrade.
To that end, AEM, a well-known performance products manufacturer based in Southern California, has produced a cold-air intake system for the E46 BMW 328, and we decided to test it. The system includes a mandrel-bent, 6061 aluminum pipe with TIG-welded fittings and brackets, a proprietary filter with a built-in air horn that reportedly helps increase horsepower throughout the rev band, and complete installation instructions (the kit also includes AEM decals and a license plate frame). All its systems carry CARB exemption (or pending CARB exemption) and carry a lifetime warranty. These powdercoated systems are also available in red, blue, silver or mirror-polished finish.
Our guinea pig car was a bone-stock BMW 328i with a little over 50k miles on it. The car was tested at AEM's dyno facility. In order to maintain consistency, baseline runs were taken just prior to the intake installation, followed by immediate tests after the intake was in place. Additionally, through the use of a scanning tool, AEM made sure the coolant temperatures were close to the same at each run, at about 195F.
With all of the third-gear dyno runs SAE-corrected, baseline runs showed a peak 172.3 wheel horsepower at 5600 rpm, with 183.7 lb-ft of twist at an early 3650 rpm. Not bad for a car that's rated at 189 bhp from the factory-figure about an 11% drivetrain loss if those factory figures are true, which seems to be the norm for most of the BMWs we've tested recently.
Once the AEM intake system was in place, the car was properly warmed up again. At wide-open throttle, the roar of the intake system had the engine singing a new song, and the car spun the rollers hard enough to measure an impressive (and repeatable) 178.8 hp at 5600 rpm with 188.4 lb-ft of torque at a slightly earlier 3570 rpm. Peak gains happened at 6300 rpm, where the AEM intake showed considerable improvements of 9.6 wheel hp and 8.3 lb-ft of torque over stock.
Even though this system relocates the air filter to suck air coming from the lower end of the car, AEM includes a heat shield to further reduce engine-bay heat warming up the intake piping. AEM reports a reduction in air temps of over 15F when the cold air intake is used in conjunction with the heat shield.
As a cold-air intake system is optimized by the amount of air reaching the filter, power gains should be increased as the car travels faster. Unfortunately, the little fan in front of the dyno could only do so much. That said, it's safe to say this system should be good for over 10 whp over stock at highway speeds.
For a few hundred bucks and an easy, 30-min. install, this AEM system is indeed a great bang for the buck for BMW E46 enthusiasts.