Despite a few blips on the radar, tradition would lead you to believe the 325i badge on the back of a BMW E90 means "less is what you get. If you want more, why don't you consider the 330i?"
However, somebody in Munich didn't get the memo and filled the 325i's engine bay with a three liter engine that's virtually identical to the one in the pricier 330i. This upgrade got people thinking about whether 330i power could be squeezed from the 325i. It was believed that in the proper hands, the inline-six is capable of stellar numbers, and it was left to Turner Motorsport to show us the way.
The E90
The latest E90 325i and 330i sedans were introduced in '06 as replacements for the E46 models. The engines were coded as new N52 units with three liter capacity for both the 325i and 330i. Horsepower was rated at 215 and 255 respectively.
For '07, the 328i and 335i replaced both models. The 328i uses a similar three liter (N53) and produces 230hp. The 335i has the twin-turbo N54 rated at 300hp. You could argue these new models make lame ducks of the '06 cars.
Or do they? TMS discovered that the potential of the 3.0 six exceeded the figures BMW published, a trend that continues with the 335i. And since BMW sold over 75000 E90 325i/330i, there are plenty of owners who need not feel cheated because they jumped onto the E90 bandwagon too early.
Unlocking secrets
TMS was one of the first companies with tuning options for both E90s. The tuning program consists of three stages: stage 1 is software and costs $1299; stage 2 adds free-flowing cats and more software tweaks; while stage 3 (for the 325i only) consists of a new intake manifold and software. For about $4500, stage 3 will give you 265hp at the flywheel, which has been proven on Turner's Dynapack chassis dyno.
This is an extra 50hp from the 325i - that's almost a 20% improvement! Driving a 265hp car with a thus-altered personality will make the decision to upgrade a no-brainer.
Entry-level Bimmer? It doesn't feel like one. Lame duck? No way. With a few other upgrades and enhancements you'll be spinning heads as well as tires.
Center stage
The 325i stage 1 package reflashes the ECU and changes the fuel, ignition and timing maps on the new Valvetronic system. Currently, you send your computer to TMS and they upgrade it for you. But Turner's future DIY solution, the Shark Injector, will be a hand-held unit that allows you to reflash the computer without removing it from the car.
On the TMS dyno, a stock 325i gave 183whp at 6270rpm with 169 lb/ft at 3459rpm. Stage 1 gave the lethargic 325i almost 10 lb/ft of torque and it began its spike where the stock car peaked - 3500rpm. The new curve peaked at 4500rpm.
Peak horsepower for the 325i is increased by over 4hp at the wheels, but the real story is in the 4000-5300rpm range where there's almost 20whp over stock.
Stage 2 swaps the factory exhaust manifolds for less-restrictive ones. Basically, the new parts feature high-flow cats that allow the exhaust gas to escape more easily. It's a relatively simple swap and doesn't require cutting or welding.
The new system flows approximately 30% more gas than stock, and adds 12whp over stage 1. Torque jumps another 10 lb/ft as well.
Stage 3 consists of an updated intake manifold and software to take advantage of the increased airflow, gaining serious horsepower. The new intake manifold features a three-stage intake channel rather than the stock single-stage. The flaps inside the manifold open different degrees depending on throttle position and ECU settings.
With this system, intake air has a more direct path to the cylinders, and the extra flaps increase torque across the rev range. This allows a 35 lb/ft increase over stock at peak.
The power number is even more impressive: 41whp at 6300rpm. This produces a stimulating 223hp at the wheels, and if you convert that to the flywheel TMS estimates you'll have 265hp. The torque similarly increases 41 lb/ft to 240.