AFE Intake System
Peak wheel-hp: 364.2 @ 6500 rpm
Peak wheel-trq: 335 lb-ft @ 4750 rpm
Peak wheel-hp gain: 6.2 @ 5570 rpm
Peak wheel-trq gain: 10.8 lb-ft @ 2600 rpm
Construction
Plastic, steel and aluminum
Pros
Uses the factory cold-air intake ducting, keeping the intake air temperature near ambient
Washable and reusable cotton air filterFactory look
Easy installation
100-percent reversible
Cons
Outside the price tag, none
Parts
MAF to intake manifold dual piping, dual cone filters, silicone couplings, hose clamps, factory airbox adapters and covers, mounting hardware, installation instructions
Tools Flathead screwdriver, 4mm Allen key
Installation Time 30 minutes
MSRP $735.29
Notes
Installation is easy and sufficiently straightforward to not need the instructions. Although the largest gain in torque was low enough in the rev range that it wouldn't be used in a high-speed driving situation, the gains from 4500 to 6000 rpm varied 3 to 7 lb-ft of torque and 3 to 6 wheel-hp. In case anyone was thinking of an aftermarket hood with air ducts, we also tested the AFE intake with the airbox covers removed, providing nothing but air directly from the dyno fan instead of scooping it from below. But this didn't net even one horsepower, proving there are no downsides to leaving the covers on. On the dyno, the intake is noticeably louder with the hood open. On the street, however, the intake can't be heard over the roar of the car's aftermarket engine-back exhaust system.
Conclusion
Initially, we hoped to see a larger gain, given the baseline power. Just a four-percent gain-typical for an intake system on most other cars-should have netted about 14 wheel-hp on this dyno. But since the E39 M5 is equipped with two large boxes from the factory, its restriction is undoubtedly much less than we'd expect from just one airbox. Special thanks to Tuning Technologies for its assistance and to Bavarian Autosport for supplying factory filter elements.