When BMW unleashed the 335i upon the world, tuning companies embraced it with warm, open arms. It was almost-M performance for less money and kept an inline-six where the M3 adopted a V8. While the 335i made 300 horsepower from its N54 twin-turbo 3.0-liter inline-six, it wasn’t the fastest car on the road. It hit 60 mph in 5.5 seconds and was electronically limited to 155 mph. This means the car was overbuilt and had plenty of room to improve. These are some of the best mods you can do, relatively inexpensively, for massive payouts, and what model year to buy.

Ditch the runflats

The 335i shipped with run-flat tires, which are designed to preserve their structure for a limited time after a puncture. What they actually did was provide inferior grip for a lot of money. If buying a 335i from someone who is by the book and kept it on run-flats, ditch them immediately for some Michelins or Pirellis, then invest in an annual roadside assistance membership, like AAA.

Get yourself a piggyback

One of the most cost-effective ways to get a lot of power out of an N54 engine is by way of what’s called a Piggyback Tuner. It’s a module that plugs into the ECU and depending on which one you get, can net your N54 up to 100 horsepower. JB 4 is the community standard and currently sells for $479. It has its limitations but is a literal plug-and-play mod. It’s the easiest and cheapest way to get 400 horsepower from your N54.

Fix your BMW 335i with a limited-slip differential

In an upset, BMW released the 335i without a limited-slip differential. Instead, it came with something BMW called “eLSD”, which was electronic traction control. For a more conventional LSD, you’ll have to replace your differential. Thankfully it’s not hard, and not very expensive, depending on the year. Start the process by removing the differential, then finding a shop that will convert it to LSD. There are several, and they will do the conversion at a discount if you send in your core differential. 

The BMW 335i came with two different types of differentials, one with a bolted ring gear and the other with a welded ring gear. The bolted one comes apart easily which makes the conversion much cheaper, whereas the welded ring gear makes life difficult and thus more expensive. BMW Tuning Co has an in-depth guide on 335i differentials. The automatic-equipped 335i had a bolted differential for its entire life except for between March and September 2007, whereas the manual-equipped 335i had a bolted differential until February 2007.

Don’t worry about 335i engine internals

There was a lot of speculation floating around the internet, debating if whether or not the N54 had forged pistons. From owner testimony and part number discontinuation, the BMW 335i had forged pistons from August 2006 until July 2007. That makes the best months to buy a manual-transmission N54 335i, with the forged pistons and bolted differential, between August 2006-February 2007. After that, BMW switched to hypereutectic cast pistons, which are still strong in their own right. However, forged pistons give extra assurance.

Is buying a BMW 335i for modding a good idea?

Even with the later hypereutectic pistons, the N54 is a solid engine. The one universal problem it had was with its high-pressure fuel pump, which BMW eventually fixed after several iterations. You can find a 335i for relatively cheap, and all of these modifications will cost (minus labor) around $2,000. If you want to increase the boost you can do that as well, just be sure to look into alternative fuels like methanol and ethanol. All in all, the BMW 335i offers a ton of performance for not a lot of money, so on paper, yes it’s a good idea. Just make sure you can afford maintenance and repairs.