Earlier this year we added a 2011 BMW 335d to our project car lineup. The car’s been trouble-free since purchase. All we’ve done is some routine maintenance (oil and filter, cabin and air filter) and we’ve made a few improvements.

First was to jettison the heavy OE wheels and run-flat tires for Kosei wheels and non-runflat Continental DWS tires.

This simple change removed over 8 lbs. of unsprung weight per corner of the car. This is a huge difference, and improves acceleration response, turn-in, and braking. In addition the non-runflat tires ride far better than the OE tires. Downside? Now a large part of the trunk is occupied by a full size wheel and tire, and spare. We’re searching for a compact spare and tool kit from a 540i or X3, which will fit this car, probably from a wrecking yard.

The big change to the car has been a Stage 2 tune from Rocketchip. The stock 335d horsepower and torque is 265/425, which is already pretty strong. We haven’t had an opportunity to dyno the car, but RC2 for this car claims 330/505. All emissions hardware and operation is intact.

Even though the car isn’t short of power stock, the tune makes a number of significant improvements. Response from tip-in is improved, the midrange is stronger, and when you roll into the accelerator at highway speeds the car just pulls endlessly. And we believe the tune removes the NA market 130 MPH speed limiter, although we haven’t had a chance to test that yet. Even with the limiter, this car can easily do things that will earn you a trip to jail if you take full advantage of its performance.

Two other benefits of the tune: the transmission behaves far better. We didn’t reflash the transmission controller, but it holds lower gears a bit longer, will downshift more readily, and pulls hard from 1500 RPM in 6th without downshifting if that’s what you want. Ironically, the increased power makes the car easier to drive gently.

The second big benefit is fuel economy. This car gets primarily highway use, but highway use in New England almost always includes time in traffic. Despite this, our average fuel economy since new is 34.7 MPG. And our most recent tank was 37.4. We doubt that any other near-luxury car with 500 lb/ft of torque and an automatic transmission could deliver that kind of economy. And it’s gratifying that tuners seem to be improving how they set cars up to deliver power, economy, and clean exhaust simultaneously. We like it.