|In previous articles, I have mentioned my strong belief that the 1996-1998 BMW 3 series cars with the M52 engines, the E36 328i, 328is, and 328ic, offer the best all around value of the E36 cars, US spec M3 models included. The 2.8 liter M52 engine is rated at 193 hp, only 4 more than the M50 than it replaced, but its 20 ft lbs torque advantage is felt at lower rpms due in part to the redesigned intake manifold and greater displacement. This, despite the 2.93 open differential these cars are saddled with in 5 speed manual transmission form, makes the 328i/328is feel much stronger at lower rpms than the M50 or M50TU powered 325i and 325is. While there are many, many modifications you can do to your 328i/is to get more out of its engine, below are a few basic guidelines for more horsepower.
Jim Conforti/Turner Motorsport/BavAuto (Bavarian Auto) Shark Injector Software. Instead of replacing the ecu with an aftermarket one, you are loading new software onto the existing one. This is really your only bet for these OBDII cars. The cars idle smoother and rev out stronger. As with all mods, best in conjunction with a cold air intake.
Some kind of cold air intake for your BMW 328. The stock airbox is not terrible, but a good cold air setup works really well and makes the car sound from 4000 7000 RPMs like an old big-block V8. I run an ECIS intake on my 325is. A friend of mine uses a universal K&N type cone filter from Pep Boys with some univeral elbow and tubing to connect it to the MAF and throttle body. He does not have a heat shield on there (his car is a 97 328i) and the car only runs perceptably better in cold weather. The heat from the engine bay and ambient temperature negates the benefits without the shield. You can either buy an air filter heat shield from any number of vendors, or make your own. Another idea is to buy some reflectex from Home Depot and make your own. I took some dryer hose and ran it down the front bumper air ducting up to the cone for a sort of DIY ram air. Not too impressive looking under the hood if you have a show car, but quite effective.
M3 OEM Exhaust or Aftermarket Exhaust. The stock M3 exhaust is a bit heavier than the 328i and 328is one, and it does away with the muffler flapper valve designed to improve low end torque. Slightly better throttle response, pulls slightly better up top, and looks great with the twin stainless tips. Great sound at wide open throttle. Some folks report dyno-proven gains with aftermarket systems, but there are better and more cost effective modifications you should probably do first instead of dropping a grand on a Supersprint or other cat back exhaust. Forget about headers for now, as well.
M50 intake manifold from a 1992-1995 BMW 325i, 325is, 325ic, or M3. I'm not saying the Schrick intake manifold is junk or not worth the money, but the M50 intake manifold is inexpensive and can be found in most junkyards or online. Where the old M50 engine continued making power at top end of the rev band, the new engines ran out of breath. One popular modification for OBDII owners is to swap in the M50/S50 manifolds. With the bigger displacements of the 328 and M3, this can really help to wake up the car and allow it breathe at higher rpms. Figure 15-20 horsepower in conjunction with the other modifications. A fantastic and inexpensive mod for cheap hp, but be warned that low end torque will feel diminished some as the power curve shifts slightly upwards. No big deal and works well with the next and final mod in our initial to-do list:
Replace that E36 2.93 open differential with a 3.23 limited slip diff from a 1996-1999 BMW M3. The tighter gearing makes even a stock 5 speed car much quicker off the line, nearly as fast as a stock E36 M3. In conjunction with the other mods, you are awfully close to stock US M3 performance. The limited slip replacing the open diff means better traction on dry and wet roads. Be advised that this mod does mean that your 328i or is will turn higher revs, with the associated increase in cabin noise from engine revs. At 80 mph, you will turn 3500 rpm in 5th gear with the 3.23 vs 3100 with the 2.93. Gas mileage is minimally affected.
These are your best bet initial engine performance mods. Next time, we will talk more about improving your Non-M3 E36 BMW's suspension. We will talk about different brands of shocks, struts, springs, sway bars, the X brace, coilovers and more.