BMW 325i/328i Tuning Guide

In the March issue we tackled some common and not-so-common power adders for the S50 3.0 and S52 3.2 motors found in '95-99 BMW E36 M3s (and some first-generation Z3 M Roadsters). We followed that in April with engine upgrades for the 2.8 VR6 12v, enjoyed in many VWs from '92-01. This month, we're heading back to Bimmerland, specifically to the successful M50 and M52 motors found in the E36 325i and 328i models.

While both engines are seen in the same coupe, four-door and convertible E36 platforms, they're slightly different. Both share the same cylinder head and block, with an 84mm cylinder bore, but the 328i's increased displacement comes from a longer stroke (84mm vs 75mm for the 325i).

M52 OBD2 328i manifold (left) vs M50 OBD1 325i manifold (right). Notice the larger intake runners on M50. The flow helps the 325i have the same power as the 328i, but reduced air velocity sacrifices low-end grunt

Since BMW sought more mid-range power for the 328i, it used a choked-down version of the 325i's intake manifold (which was also found on the E36 M3 3.2 in '96). The resulting 206 lb/ft at 3950rpm significantly bettered the M50's 181 lb/ft at 4200rpm. However, the M52 manifold's decreased intake runner diameter cost it top end grunt. That's why both the OBD1 M50 engine found in the '92-95 325i and the OBD2 M52 found in the '96-98 328i share the same peak 189hp rating at the flywheel.

As we're always keen to point out, you don't have to live with stock power any longer. We've hunted down some key tuners who take these cars to the next level.

Bear in mind, we're assuming horsepower gains over a stock 170hp to the rear wheels (whp) through a five-speed manual transmission on a chassis dyno. Different cars and different dynos will vary, and we don't care to use flywheel guesstimates since they're usually quoted with different assumed percentage losses and are rarely backed by actual engine dynos.

Note: the quoted prices do not include labor costs. They are simply parts prices.

Evo2 intake from Eurosport High Performance

$0-1000
An easy-to-install, bang-for-the-buck upgrade is usually an intake system. Sure, you could get a K&N or aFe drop-in filter from BMP Design and retain the factory airbox, but the conical filters in a cold-air intake (CAI) system will give more power.

Companies like Active Autowerke (Active), Advanced Flow Engineering (aFe), BMP Design, Eurosport and Turner Motorsport (TMS) offer intakes for both cars. You've also got companies like Dinan, East Coast Induction Systems (ECIS) and VF-Engineering who offer CARB-certified systems for street-legal use in California. Expect to pay between $180-400 for these kits, and to achieve power around 175-177whp. You'll also enjoy a new roar under the hood at wide-open throttle past 5000rpm.

Turner Motorsport lightweight underdrive pulley kit

The next quick power gain is a set of lightweight underdrive pulleys that replace the alternator, power steering and water pump pulleys. These liberate some lost horsepower from the parasitic drag of the factory units. Not only that, but the hard-plastic factory pulleys are known to crack over time and fail (I had this happen on a '96 M3 water pump pulley!).

Eurosport, evosport, Rogue Engineering and TMS sell 6061 CNC aluminum pulleys for around $225-250 that should net you 4-5hp at peak, with a constant 3-4 lb/ft through the rev range.

Dinan OBD1 chip

Depending on which company's intake you chose, you've got up to $500 left to spend before getting into the next price category. This means you can get software, which Active, Dinan, ECIS, Eurosport and TMS sell between $250-400, with 328i software being more expensive. The software not only bumps ignition and revises fuel maps for optimum power, but it removes the factory speed limiter so that 150mph top speeds are possible.

When putting the intake system, pulleys and software together, expect to have a noticeably faster car that's probably close to 185whp.

An alternative for your $1000 would be the Eurosport 325i cam kit. This upgrade uses factory BMW cams from a '95 M3 and includes Conforti-tuned software, as well as its Evo2 carbon intake for $999. The kit has shown sizeable gains, with peak horsepower reaching 195whp, but keep in mind the 6-8 hours of labor