BMW’s N20 engine featured in the 228i, 328i, 428i, 528i, as well as other 28i variants, did not built up the greatest aftermarket and tuning reputation, as the engine has been touted as fragile. Although the N20 is not the strongest motor there is still plenty of power to be unleashed with a tune and basic bolt-ons. In stock form, the N20 was quoted right around 240hp and 258tq, however, independent testing in the real world shows the engine is stouter than BMW suggests. Dyno results place the actual numbers in the ballpark of 275hp and 290tq. A tune and a few basic mods, all for under $1,500, can boost the N20’s power and torque into the 350 range.
Before Tuning Your N20: Spark Plugs and Ignition Coils
Adding power to any engine typically brings forth issues that go un-noticed when the car is in stock form. Two of the most common problems that pop up when tuning your BMW engine are spark plugs and ignition coils. The newfound power requires a stronger spark to ignite the increased air/fuel mixture, and old, worn, or faulty spark plugs and coils cannot generate enough of a spark to fully burn the air and fuel.
Jake and I talk about spark plugs and ignition coils a lot as we both experienced the same thing on our N54 engines. We were so excited to install our tunes and a few bolt-ons, only to go out for the first drive with an engine that was running poorly. There was nothing worse than having to wait a week to get new spark plugs and ignition coils.
Typically spark plugs should be replaced on stock N20’s every 40,000 – 50,000 miles, and ignition coils every 50,000 – 60,000 miles. However, a tune and bolt-ons cut the life of these parts in half, roughly. If you know you have not replaced the N20 spark plugs or coils within the recommended time it may be a good idea to do so before tuning the engine. The OEM products can be found below:
Other Things to Consider Prior to Tuning
Spark plugs and ignition coils are not the only issues that may come to light after modifying your BMW N20. A few other things to look out for may include, but are not limited to:
- Test and check for boost leaks
- Compression Test
- Suspension, brakes, and tires
- Fuel system
- Engine Fluids
Boost leaks may not be significant enough to create any issues on stock boost levels, however, with the increased boost a small leak may become more significant. A compression test will ensure your engine internals are running properly, and there are no serious internal issues that may pop up after tuning. With the increased power you will likely put more strain on your brakes, suspension, and tires so it is important these parts are ready to handle the task. Additionally, increased power will require increased fuel flow, and will subject the engine to additional heat.
Five BMW N20 Mods For 350 Horsepower
Without further ado, let’s jump in and discuss the five mods for your BMW N20 that will increase your horsepower and torque into the 330-350 range. A tune is the first and most obvious modification, followed by a few bolt-ons. These include an upgraded intake, front mount intercooler, and a catless downpipe. Typically, engines with these 4 mods are referred to as FBO, or Full Bolt-On. Some consider a full exhaust system an important part of being FBO, however, a catless downpipe is the most important exhaust component that will lead to the most significant increase. A full exhaust may net a few extra horsepower, which is insignificant compared to the cost. The fifth “mod” we recommend for the BMW N20 is a small mixture of E85 fuel.
Mod List for a 350HP BMW N20
Jake and I, along with many others in the turbo BMW community, run a JB4 on our BMW’s. The JB4 is a piggyback tune, which is a simple plug-and-play harness that installs directly on the ECU. This tune adds roughly 60hp to an otherwise stock BMW N20, and may add up to 100hp on a FBO N20 with a small E85 mixture. The JB4 tune sells for $479 brand new, and used tunes can be found for closer to $300. This mod is the best bang for the buck, and if you were going to only put one modification on your BMW N20 then we highly recommend a tune, and specifically the JB4. Another excellent feature is the ability to couple a back-end flash tune with the JB4. A back-end flash will net additional power due to having better control over fueling, timing, etc., while allowing the JB4 to function with its advanced boost control and safety features.
Price: $479 new, ~$300-350 used
Horsepower Gains: 60-100hp, depending on supporting mods
One of my personal favorite mods on my N54, a catless downpipe will not disappoint on the N20 either. The best exhaust on a turbocharged car is no exhaust after the turbo; for most of us, this likely is not practical for daily driving on public roads. The pressure drop from pre-turbo to post-turbo plays a significant role in allowing the turbocharger to spool and build boost. Removing the catalytic converter from the downpipe will increase horsepower and torque by 10-20. Additionally, a catless downpipe will allow the turbo to spool quicker, which means torque hits instantly and is a great feeling on the butt-dyno. Lastly, a catless downpipe produces a more aggressive exhaust note without sounding intrusive or droning during normal cruising. Lay into the throttle and it really brings the sound to life, however if you set cruise control on the highway the exhaust still sounds completely stock.
Horsepower Gains: 10-20, and faster turbo spool
While peak power gains are not quite as impressive as the tune or catless downpipe this mod ensures consistent performance throughout the rev range by keeping IAT’s (intake air temps) down. Cooler IAT’s mean the N20 will produce more horsepower later in the rev range and prevent the turbos from heat soaking. On a hot summer day, you can feel the effects of heat soak on a stock intercooler; after a few wide-open throttle pulls you can really begin to notice the decrease in performance. Additionally, and most importantly, cooler intake temps will reduce the risk of the N20 pre-detonating or knocking. This is extremely helpful in ensuring the longevity of your BMW N20 engine as engine knocks may be harmful to engine internals.
Price: $380 for 5”, or $480 for 6.5”
Horsepower Gains: 5-15
**Most importantly, consistent performance and reduce chance of engine knocks
This mod found its way a bit further down the list as the performance benefits are up in the air. An air intake will only increase horsepower if the factory intake is not able to flow enough air. It appears the BMW N20 factory intake can flow enough air for modified cars, and as such an upgraded intake has minimal performance gains. That being said, FBO N20’s on E85 mixtures may see a few horsepower and torque from this mod. Regardless, we still highly recommend this mod as the sound is absolutely intoxicating, in our opinion. Under boost you can really hear the turbos come to life as the air intake begins to pull in as much air as possible.
Horsepower Gains: 0-5
**Intoxicating sound, in our opinion. Power gains are likely minimal until you run into a wall where the factory intake simply cannot flow enough air.
E85 Fuel Mixtures
The last “modification” to take your BMW N20 to the next level and boost horsepower and torque into the 350s, or more. We may be mentioning E85 last, however, this mod has some serious potential. E85 has too many benefits to list in a sentence so let’s make a quick list:
- Increase Horsepower & Torque
- Burns significantly cooler than gasoline
- Reduces chance of knocks/pre-detonation
- Cheaper than gas (though at the cost of some fuel efficiency)
Not only does E85 naturally burn cooler than gasoline, it further benefits from burning at a lower stoichiometric ratio than gasoline. This means more fuel is required per each part of air in the cylinder. More fuel injected into a cooler engine (as compared to regular 91/93 octane) significantly reduces the chance of engine knocks. Horsepower and torque may see drastic increases due to cooler temps and less risk of engine knocks, which allows the engine to run more aggressive timing. The JB4 and stock fueling system on the BMW N20 are compatible for a roughly 40% mixture of E85 fuel. Higher mixtures may be used with a flash tune or JB4 coupled with the back-end flash as this will allow the ECU to flow the additional fuel required. Horsepower gains depend greatly on the specific amount of E85 used.
Price: Depends on area – comparable to lowest grade fuels such as 85/87 octane
Horsepower Gains: 10-50+
**Reduces risk of engine knocks; helps engine run cooler internally
How to Ensure Your N20 Remains Reliable After Tuning
Some people have concerns regarding reliability and longevity of their engines with modifications compared to stock form. Of course, those concerns are well warranted as increasing horsepower does increase engine heat as well as the many other stresses put on an engine. An engine knock can suddenly become devastating at higher power levels, so it is important to ensure your N20 is running well after mods. As the N20 is not the strongest of recent turbocharged BMW engines, here are a few recommendations:
- Limit boost to 22psi
- Watch AFR’s – ensure engine is not leaning out
- Fluids such as oil and coolant are changed within recommended time frames
- Or sooner if driven aggressively
- Let oil temps warm up to 160F before pushing the engine
22psi seems to be the generally accepted boost for the N20’s factory internals. If you want to push the car any further, it may be time to consider forged internals and the necessary supporting and engine cooling mods. Pay attention to your air-fuel ratios; the N20 has been known to run a bit on the leaner side, which may be a recipe for blown motors. A properly set up, conservative tune and occasional monitoring will help mitigate this risk. Ensure your N20 has proper oil and coolant flow to maximize engine cooling and reduce the risk of oil starvation.
Remember, N20 powered BMW’s were not designed to be all-out track cars and pushing the car too hard around long, fast corners and heavy braking may lead to oil starvation situations. Increased boost will cause the turbocharger to run hotter, and the turbo heats up a lot faster than the oil does. Cold oil splashing on a hot turbo and hot turbo seals is not recommended for the longevity of the turbo. The JB4 does limit the engine to stock boost levels until the oil reaches proper operating temperatures.
Overall Thoughts on N20 Tuning
Although the BMW N20 is not known for its strength and durability, the engine is capable of producing and handling power levels significantly above stock. No offense to the N20, but it is not quite the same engine as the N54, N55, B58, or S55 engines. You cannot simply dump a bunch of power into the N20 and expect it to handle the power as well as the larger 6-cylinder engines mentioned above. The BMW N20 requires a slightly more conservative and cautious approach to tuning and modifying.
Ensure you are running proper supporting mods such as an upgraded intercooler, and E85, if available, as these mods will assist in reducing pre-detonation risks. Play it safe, and the BMW N20 is a great engine that really comes to life with a tune and bolt-ons. For under $1,500 your BMW N20 may be capable of producing upwards of 350hp. Impressive numbers for a small 2.0L 4-cylinder engine, just remember to play it safe and do not risk your engine to stretch for a few extra horsepower.