BMW M50/M52 Engine - 325i/328i Tuning Guide - Eurotuner Magazine

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).

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.

$0-1000An 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.

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.

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...

$1000-2000
Once you have an intake, pulleys and software, the next upgrade is a cat-back exhaust. Companies like Active, B&B, Dinan, evosport, Rogue, Supersprint, TMS and UUC Motorwerks all have one, and prices range from $550-1299. The least expensive is sold by UUC, the most expensive by Dinan.

>> Installation is usually a simple 1-2 hour task. You'll get a handful of horsepower, the car will benefit from a more aggressive sound and there could be a 10-20 lb weight reduction over the stock system.

For $1438 you can treat your stock 328i to 188whp with a performance package from Active. Its CAI, third-generation cat-back exhaust and software have been tuned in-house on its Mustang Dyno. For the 325i, the same upgrades should get you similar power but cost $1314. These prices could drop since Active is hoping to lower the price of its software, so call them first.

$2000-3000
Dinan's normally-aspirated upgrades for these two engines will net a claimed 220bhp at the flywheel, which we estimate to be around 195whp. The upgrades include Dinan's software, CAI, exhaust and larger throttle body for $2286.

Eurosport's cam kit for the OBD2 328i features its M50 manifold conversion kit, Evo2 intake system, Conforti software and cams from the '96-99 M3 3.2 for $2146 (manifold sold separately).

The company recommends you source the manifold but can supply a new one for an extra $497. The larger manifold sacrifices mid-range torque - a loss of 10-15 lb/ft from 3200-4200rpm - but the trade off is superb at the top end. While the stock car peaks at 181 lb/ft at 4000rpm and immediately starts to fall off, the kit helps sustain 185-190 lb/ft from 4300-5800rpm. The end result is a peak gain of 40 lb/ft and 45whp at 6000rpm, equating to 205whp total.

Eurosport also tested the kit with a factory M3 exhaust (you can find used ones) and got 209whp - now you're in E36 M3 territory!

$3000-4000
Active has supercharger systems for both the 325i and 328i that are currently on sale for $3995. Breathing through a factory exhaust, you can expect 250whp at 8psi, and over 255whp if you throw in Active's Gen3 cat-back exhaust for an extra $690.

The supercharger is a Rotrex C30-94 and the kit includes mandrel-bent tubing, high temp hoses, high-flow injectors, front-mount intercooler, oil cooler, bypass valve, hardware, software and an illustrated manual. If you're wondering about reliability, AA reports it's sold over 600 of these kits already.

$4000-5000
VF-Engineering sells a centrifugal supercharger for both engines. Using a Vortech V2 SQ SC polished supercharger regulated to 6psi, the kit also features OEM BMW idler pulleys, CNC brackets, OEM high-flow injectors, Bosch bypass valve and GIAC software. The kit retails for $4500 and will net you 235-250whp. The 328i gets the lesser horsepower but more torque; 220 lb/ft at 5200rpm, compared to 212 lb/ft at 6200rpm for the 325i.

Over $5000
Dinan has a centrifugal supercharger for $6500. Although the company doesn't quote whp numbers for the kits, they've quoted 255-258bhp which we've converted to an estimated 225-230whp, with 200 lb/ft to the wheels. While the price is the same for manual 325i and 328i, automatics cost about $500 less.

Active is considered the pioneers of E36 turbocharging. Even though it has discontinued its turbo kit for the 325i on the website, it sells them to customers who demand one.

The AA stage 1.5 kit uses its stage 2 intercooler and features a Mitsubishi TD06-H turbo with a 120mm housing to suit the engine displacement. There's no reduction in compression, so the head doesn't have to be removed. At 9psi, the $7995 kit is good for around 295whp at 6250rpm, with 275 lb/ft at 5000rpm - a good turbo kit will get you a fat torque curve. In this case we're talking a minimum 250 lb/ft from 4000rpm to redline. Add a boost controller, larger injectors and some race fuel, and this kit should be good for 350whp.

For the 328i only, Eurosport offers its twin-screw supercharger. The stage 2 system uses the 1.7 liter Opcon Autorotor and Laminova intercooler core that are integrated into the CAD-designed manifold. Boost is regulated to 9psi, and air is cooled by a water-to-air intercooler with front-mounted heat exchanger. For $8495, stage 2 delivers 320whp. With a set of M3 cams and an M3 cat-back exhaust, the company saw 333whp at 6800rpm with over 270 lb/ft available from 4000-6200rpm. For those interested in saving money, Eurosport also offers a non-intercooled stage 1 twin-screw setup with undisclosed power ratings.

Special Concoctions
If you already have E36 M3 cams but need software, companies like Eurosport, TMS and Active have programs tuned for this setup. Since a header-back exhaust system, CAI and the M3 cams can get you around 200whp, you might want to do it soon.

It's no secret a 3.0 or 3.2 liter '95-99 M3 motor will fit the 325i and 328i since they share the same chassis. But don't forget to add the wiring harness along with an M3 tranny and clutch.

Turner Motorsport is able to swap your 325i for an M3 motor in one to three days for approximately $1700 labor plus parts. You can supply your own motor or they will find one for about $4500-6500, plus an M3 gearbox for around $900, plus a few ancilliaries.

If your engine is torn apart, you could swap in a 3.2 short block since the M3 shares the same cylinder head, but you'd still need the right software to run the engine. If this sounds interesting, you can source used and newly built engines from Bavarian Engine Exchange. Then you'd be starting from a 210whp level that can be easily improved after reading our S50/S52 tuning guide (et 3/07).

For those tearing their motor apart without interest in forced induction, Active suggests using your stock 325i or 328i block and pistons and installing S50 crank and rods from a '95 M3. Your displacement will be bumped to 2.9 liters with the compression increasing to about 11.5:1.

The neat thing about this setup is Active already has software running with factory M3 cams that nets 215-220whp using an AA track pipe (no cats) and muffler. That's more power than a stock E36 M3. Additionally, AA can order you a set of custom-ground cams that reportedly increase that figure over 240whp in some cases.

Lastly, if you have a 325i or 328i and loads of cash, you may want to check out ICS Performance. These guys took a stock 2.8 liter to 635whp with a GT35R turbo running 29psi on the stock ECU (race fuel, of course) - that's more power than any stock E36 M3 engine has seen, all thanks to the thicker wall between the cylinders on M50/M52 blocks. And now the same 2.8 block with forged internals controlled by an Electromotive TEC3 engine management is seeing four-digit dyno readouts.

While the M50 and M52 engines were found in the E39 (528i and 525i) as well as in the Z3 2.8 chassis, research for this article was done specifically for the E36. That said, the majority of these upgrades should work with these other vehicles. However, exhaust and forced-induction systems, where available, will be different.