Building a 400WHP N55 with 5 Simple Bolt-Ons
We wrote a similar post for the N54, which seemed to be a popular and informative post for those looking to learn more about the engines capabilities. For those who read our post about the BMW N54, it should be noted the N55 is not quite as capable as the N54 mod-for-mod for two reasons. One – the N55 features a twin-scroll single turbocharger compared to the N54’s true twin-turbo set up. Two – the N54 is an older engine, allowing additional time for aftermarket companies to develop further advanced tunes and performance products. However, BMW’s N55 still delivers impressive performance for excellent value. This post will outline the necessary modifications to push your N55 to the 400whp mark; all for under $1500.
Before Tuning your N55
Creating extra horsepower requires creating additional combustion within the engine. Extra combustion requires extra spark and results in increased internal temperatures.
The N55 OEM spark plugs are great for stock cars or N55’s that are modified but still running stock boost levels. Increasing boost levels (ie. running a JB4 or other piggyback tuner) results in increased combustion temperatures and can easily result in misfires and pre-detonation if your spark plugs and ignition coils are old or ‘too hot’ for the engine temperatures.
We recommend that anyone intending on increasing boost levels should replace their stock plugs prior to tuning it or opt for 1-step colder spark plugs which won’t misfire or pre-detonate from the increased combustion temperatures.
To recap: upgrade or replace your spark plugs and ignition coils prior to modifying your N55!
- N55 OEM Spark Plugs: for tuners who aren’t increasing boost levels or don’t plan on running above 350whp
- N55 1-Step Colder Spark Plugs: for tuners who are going to run a piggyback tuner and other mods and expect >350whp
- OEM Ignition Coils: these should be used regardless of horsepower targets and should be changed with your spark plugs
Our readers get 5% off any order of N55 spark plugs or ignition coils by following the links above and using code “BMWTUNING” at checkout!
400WHP BMW N55 Mod List
Burger Tuning’s JB4 is among the most common tuning options for the BMW N55 platform, and for good reason. Their tunes are easy to install and Burger offers phenomenal product support; the amount of information regarding the JB4 on the BMW forums is exhaustive. The JB4 allows for on the fly map switching through the steering wheel buttons. This means you have the option to change your tune (each map is a unique tune) in a matter of seconds. In addition to the JB4, there are many other tuning options for your N55. In the near future, we will write a post detailing the different options and benefits of each. For now, we highly recommend the JB4 as both Jake and I run the JB4 on our N54’s and strongly believe it is the best tune on the market.
Horsepower Gain: ~60WHP (75hp crank)
Price: $479 new, ~$350 used – Purchase it on eBay here
Pro Tip: For those looking to make additional power try coupling a back-end flash with the JB4. MHD offers some excellent back-end flash options. Shortly, we will write a post highlighting the benefits of stacking a JB4 and back-end flash.
Once again, Burger Tuning’s (BMS) intake is one of the most common options for the N55. I won’t diverge too much into the specifics of the different performance intake options, as they all function in more or less the same way. The BMS performance intake retains the OEM cold air ducting and the heat shielding bottom portion of the airbox. A performance intake allows your N55 to pull in more air leading to faster turbo spool, more power, and an intoxicating sound. Although the power and turbo spool gains are great, my favorite part about the performance intakes is the sound. An upgraded intake really brings the sound of the turbo spool to life.
Horsepower Gain: ~10WHP and faster turbo spool
Price: $250 – Buy it on Amazon
Pro Tip: Try out Burger Tuning’s cowl filters (cabin air filters). These filters remove roughly 10 pounds of weight, promote better engine cooling, and once again, the sound is intoxicating.
The downpipe is part of the exhaust that is bolted directly to the turbocharger, and is one of the most important exhaust components on a turbo car. In short, the drop in air pressure pre-turbo to post-turbo is an important factor that assists in spooling a turbocharger. Despite misconceptions that a car requires some exhaust back-pressure, the best exhaust for a turbo engine is no exhaust at all. Of course, no exhaust likely is not the best option for those of us daily driving our cars on public roads. This is where a catless downpipe comes into play. Eliminating the catalytic converter in the downpipe reduces back-pressure, thereby enabling the turbo to spool faster and generate additional boost. Additionally, the catless downpipe creates an aggressive exhaust note that is not overly intrusive for daily driving or long road trips.
Horsepower Gain: ~15-20WHP and faster turbo spool
Price: $290 – A downpipe is a more challenging install for novices. Expect an installation cost of roughly $150-200, if you do not feel up to the challenge.
Pro Tip: Now that your car likely will not pass inspection, try registering it out-of-state to avoid inspections. Just kidding – I definitely do not do that. I only run my catless downpipes on track days.
One of the downsides to turbochargers is the amount of heat they produce. Most turbo car drivers that push their cars have likely experienced something similar to the following: You go WOT for this first time on this cruise and do a quick 0-60 run. The car felt extremely powerful as you rocketed to 60mph. Accordingly, you come to a stop and try it again, but this time the engine feels less powerful. By the third 0-60mph run the engine feels dead. The truth is – your butt dyno is not wrong. Turbo engines are highly susceptible to heat soaking; as the turbochargers continue to spool they create more and more heat. This leads to a drastic increase in IAT’s (Intake Air Temperatures), which then results in the DME pulling timing and boost. An intercooler helps cool the hot air after it leaves the turbocharger, however, the OEM intercooler struggles to keep up with a modified car that is running extra boost.
A larger intercooler is more efficient and effective for reducing the IAT’s as it has a larger surface area to cool the passing air. Since colder air is denser, this will lead to a gain in horsepower. Most importantly, a 7” intercooler will help your N55 remain consistent as your push your car hard. An intercooler can also increase reliability, especially at high power levels, due to its ability to eliminate heat soak and assist in preventing the engine from knocking or pre-detonating.
Horsepower Gain: ~10-15WHP, most importantly consistent performance
5. E-85 Fuel
For those who have access to E-85, a corn based alcohol fuel, I highly recommend using a small mixture in your tuned N55. Please note – we will post additional information on running E-85. Not all tunes support E-85, and your cars tune is a crucial factor in determining how much E-85 you can mix into your tank. Map 5 on the JB4 is an auto-tune, which can read your cars fuel and adjust the tune based on the fueling. However, map 5 can only compensate for a certain amount of E-85. Do NOT simply dump ½ a tank of e-85 into your car and expect it to perform better. As mentioned, we will post more information and in the mean-time the forums are littered with useful information.
E-85 burns at a stoichiometric ratio of 9.8:1 as opposed to gasoline’s ratio of 14.7:1. This means that you need 9.8 parts air per 1 part of e85, while gasoline burns at 14.7 parts air to 1 part fuel. In other words, E-85 requires roughly 35% more fuel for each burn cycle. Additionally, E85 has a high “latent of heat evaporation”; as the fuel changes from liquid to gas it absorbs a lot of heat. The heat absorption effect of E85 provides many benefits. As mentioned with the FMIC, cooler air is denser which increases horsepower. In the case of E85 the effects are magnified as the fuel is sprayed directly into the cylinder. Furthermore, the cooler cylinder temperatures significantly decrease the chance of the engine knocking or pre-detonating. Horsepower gains may vary greatly depending on the tune, supporting mods, and mixture of E85.
Horsepower Gain: Up to 30-40WHP on stock turbos
Recommended Supporting Mods:
Once you push you N55 upwards or beyond the 400whp mark there are certain parts that may present themselves as problematic at higher horsepower. These mods are not required, and in most cases, do not add any additional power by themselves. However, they may aid in generating more power through existing mods and/or keep you from being stranded on the side of the road.
The chargepipe in the N55 is certainly a weak point at higher power and boost levels. The OEM pipe is made from plastic, so it is likely a ticking time bomb when pushing your stock turbos to the limit. An upgraded chargepipe will not provide any true performance benefits, but it will ensure your car is ready for the additional power. Some people like to upgrade the chargepipe before modifying their BMW. However, others like myself, are waiting for the day the OEM chargepipe explodes until looking for a replacement. Prices for metal chargepipes start around $200 if you opt to keep the factory diverted valves, and can jump to $500+ if you are looking to replace the diverter valves with blow-off valves.
2. Low-Pressure Fuel Pump (LPFP) – Higher E-85 Concentrations
In most cases, with stock turbochargers your OEM LPFP will flow enough fuel to support the modifications. However, those who want to run higher E85 mixtures may want to consider LPFP upgrade options. As discussed, E85 requires 35% more fuel for a given amount of air; at high boost levels this will max out your LPFP and limit your N55’s performance. For mixtures above 40-50% E85 the LPFP upgrade is a must. A LPFP upgrade alone will not increase power, however, it will allow you to run more E85.
Although the BMW N55 falls behind its N54 counterpart mod for mod, the N55 remains an impressive, easily tune-able engine that is capable of roughly 400whp with a few simple bolt-on’s and an E-85 mixture. The N55 remains a reliable, poised engine when modded; during typical cruising the engine feels stock, but apply heavy throttle and the N55 quickly reminds you it is far from stock. Overall, BMW’s N55 is a tuner-friendly engine capable of making, on the stock turbo, plenty of power to satisfy a majority of enthusiasts, all while remaining reliable and driveable in all conditions.
For more on the BMW N55 reliability: read our post about common N55 engine problems.