With most of the preventative replacements and maintenance, there isn’t much you can do to improve performance. However, once you’ve completed that maintenance, you can begin to modify your 135i with performance parts that give you more power and, in some cases, remedy some issues you might otherwise encounter. The 135i, especially the early N54-powered version, has a host of popular upgrades that have proven themselves as a quick roadmap to incredible power potential. If you have run through our previous article that details the common maintenance concerns, then now is the perfect time to take advantage of that easily accessible power. Today, we’ll outline the most popular upgrades for your 135i to make it handle and perform better than BMW ever anticipated.
Intakes: The N54 is twin-turbo, so it has two intakes. This is a fairly involved process because there is a lot to remove and install, which makes it one of the more complicated engines to upgrade with aftermarket intakes. The Turner Motorsport Turbo-Side Intakes are our favorite choice for both cleaning up the engine bay as well as making real, measurable and fun power. For the N55 variant, we also have a number of upgraded intakes, but there will only be one tube thanks to the twin-scroll single turbo used in this application.
Vacuum Hose Relocate: Once you’ve upgraded to the Turbo-Side intakes, you’ll notice a rather unsightly vacuum hose snaking its way around the engine bay. Our new Vacuum Hose Relocation Kit replaces that rubber hose with a silicone version that tucks neatly away so your engine bay looks cleaner and more put together. We highly recommend this kit whether you choose the Turner Motorsport intakes or any other aftermarket intake system.
Downpipes: Upgrade your 135i downpipes with a set of performance versions that open up the airflow for more power and better sound. These are necessary if you want to run performance software with the best results.
Intercoolers: The 135i intercooler and charge pipe upgrades available are also required for higher-stage software. The basic series of modifications include the need for higher-volume intercoolers to allow the charge air temperatures to reduce intake air temperatures for more power and better consistency. What this means is that your turbo or turbos will spool faster and produce more horsepower over a wider range. When paired with an appropriate tune, you can maximize the potential output and efficiency of your turbos by introducing the correct amount of fuel with a smoother map.
Exhaust: Following the downpipe upgrades, a performance 135i exhaust will not only sound fantastic but also allow you to run that software we keep mentioning. The improved exhaust will help with your overall horsepower output as well as provide endless entertainment thanks to the throatier and more enjoyable exhaust tones.
Software: Ok, this is the bow that ties all the power upgrades together. With a tune for your 135i software, you can increase the effectiveness of all your bolt-ons. Software tunes, like the popular Burger Motorsports JB4 and COBB Accessport, piggyback on your existing ECU software and essentially overwrite certain functions with programming designed to support certain upgrades. What is commonly referred to as “Stage 1,” “Stage 2,” and “Stage 3” is derived from the software upgrade and list of supporting modifications. A Cat-back exhaust and intake upgrades, paired with a software reflash, is generally “Stage 1.” Adding an intercooler and downpipes is generally known as “Stage 2.” Lastly, making significant changes would be the use of upgraded turbochargers, like a big single turbo upgrade for the N54, with a better exhaust manifold and higher-output turbo, bigger injectors, and perhaps E85 flex-fuel or methanol injection is where the idea of “Stage 3” is defined.
Turbo Upgrades: Making your N54 a big single turbo or going for a more powerful twin-scroll turbocharger in your N55-powered cars are incredibly popular for those hoping to push the boundaries of what’s possible from your 135i. DocRace is incredibly well known in this arena, with kits able to handle up to 1,000HP. If you want the baddest BMW on the block, this is where you should set your sights. Other options include Vargas Turbo Technologies and Pure Turbos.
The suspension department is predominantly left to your preferences. If you just want a bit of a drop and a handling upgrade, then you should opt for H&R lowering springs and performance dampers, like KONI or Bilstein. If you want extreme performance, adjustable coilovers are your best solution. For the show stance and scene points, you’ll want Air Lift Performance air suspension. It’s pretty much that simple, at least until you get into dialing in suspension settings for racing, which is a bit outside of the scope of this overview.
With this list of upgrades, you should be well on your way to a stout little performance coupe. Your 135i can easily become an unbelievable powerhouse with a few bolt-ons and look the part with a lowered ride height. Thankfully, the brakes, wheel options, and interior are already quite capable and look incredible. Just these upgrades, after that critical maintenance, and you should be set up to achieve some real greatness. Check out our full catalog of BMW 135i parts and accessories to make yours the exceptional vehicle it always could have been.