The N54 Tuning Guide to Intercoolers (FMIC’s)
Front mounted intercoolers are extremely important applications on turbocharged cars. Intercoolers cool the compressed air created from the turbochargers, reducing the temperature and increasing the density of the air that is fed into the engine.
Cooling the air makes the air more oxygen rich, therefore improving the combustion in the engine by allowing more fuel to be burned. As we know, more combustion equals more power. Most importantly an intercooler is an important reliability mod as it keeps air temps more consistent which helps regulate and keep the air to fuel ratios at safe levels.
Why do you need an Upgraded Intercooler in your N54?
The OEM intercooler on the N54 is notoriously small and restrictive.
Turbochargers compress air, which naturally creates heat. N54’s running above stock level boost create additional heat, up to 200°C, which is why an upgraded intercooler is crucial for performance and reliability at increased boost levels. The factory intercooler isn’t well-equipped to handle temperatures of these levels. On a stock intercooler, this will cause high air intake temperatures which decreases the oxygen content of the air significantly. This results in decreased performance and adds additional thermal load to the cylinder head and valves and can cause engine damage.
Benefits of an Upgraded Intercooler:
- Higher boost levels supported due to decreased air intake temps
- 15-20whp increase due to higher boost, better timing
- Less prone to engine knock and pre-detonation
- Improved engine reliability due to consistent intake air temps
- Improved engine efficiency
- Better throttle response (for some)
An upgraded intercooler doesn’t necessarily add additional horsepower, but it will allow your car to produce the amount of power it is supposed to. It restores power loss which is where the 15-20whp gains will come from.
The Two Types of Intercoolers
Intercoolers aren’t all made equal. There are two primary manufacturing/design methods and each create a different end performance result. It’s important to take these factors into account when buying an intercooler.
- Bar & Plate Intercoolers: these intercoolers have a heavy core construction which creates temperature inertia. Under load, the core will take longer to heat, but also longer to cool down when the load decreases. This is ideal for daily drivers but isn’t great for track-only N54’s since it creates constant cooling performance at varying loads throughout the full load range. To break down the jargon, most of the aftermarket intercoolers you see will be Bar & Plate and this is what we recommend unless you are building a track star.
- Tube & Fin Intercoolers: this design uses a light core which makes for quick heat transfer. It will take and release temperatures much more quickly than the bar & plate design. This is ideal for track usage because the cooling performance is a lot more dynamic and will vary based on the amount of load (throttle) you are applying. This is fine for street use too, but most of the aftermarket bolt-ons will be bar and plate. Tube and fins usually weigh less, but are more flow restrictive. They are also more prone to damage on front mount applications.
The OEM N54 intercooler is a tube & fin design, but it is designed for low boost and low air flow which cannot keep up with tuned cars.
Here is a picture of bar and plate vs tube and fin intercoolers:
If you didn’t read any of the above, stick to Bar & Plate intercoolers unless you are building a track-only car.
Intercooler Core Design and Why It’s Important
The outside core uses the wind hitting it for heat exchange. The outside core can either be low or high density, with higher density resulting in better cooling performance. What is behind the outer core is also important and sub-optimal outside core design can block the internal parts. The important thing to remember is that high density cores are better. Here is a picture of the difference:
The left is a low density core, and the right is high density.
The interior of the intercooler has an additional core, similar to the outside core. This core can also be either high or low density. The inside core is what cools the air that is going into the engine for combustion. High density internal cores provide the best cooling performance but also result in a big decrease in pressure, which increases the load on the turbocharger and ultimately results in less stability and a shorter lifespan for the turbocharger.
Aftermarket intercoolers have to have the perfect balance between cooling performance and pressure drop, which requires a lot of testing and R&D. Cheap Chinese (aka eBay) intercoolers are not properly tested, developed, or engineered, which is why we highly recommend getting an intercooler from a reputable company in the space, not eBay.
End Tank Design
The end tanks are both the sides of the intercooler where the air flows in and out of. The end tank is important because a poorly designed end tank can result in decreased pressure.
Here is an image of a horrible, almost non-existent end tank:
It’s not a great angle, but you can see the left and the right sides are just flat, like the intercooler is a perfect rectangle. When the air is trying to exit, it has zero direction or flow, so it gets pushed right into the wall, which creates turbulence inside the intercooler and will result in decreased pressure.
Here is what a proper end tank looks like, it should have some curvature or design that helps guide the air out of the intercooler.
In the end, the design matters. All intercoolers are not equal. My most important piece of advice is to buy a reputable product. You can trust that a reputable company has done the the proper design testing and engineering to make the best intercooler.
If you buy a reputable intercooler, you don’t have to worry so much about design as they have already figured it out for you.
N54 Intercooler Size & Fitment
Since we are going to buy an intercooler from a good company (right?), the most important thing for us to figure out is: what size intercooler should I get?
People tend to have a misconception that the bigger the intercooler is, the better the performance and results. But this is false. Intercoolers are all about flow and efficiency and the mods your car currently has are the most important determinants.
Intercooler sizing should be completely dependent upon what existing mods your N54 has.
Putting a 7.5″ FMIC on your bone stock N54 would most certainly result in poorer performance compared to a 5″ FMIC as it will take a lot longer for your turbocharger to fill the FMIC with charged air. More effort to fill the FMIC means more heat will be generated, and you will have a lot more turbo lag.
The scenario looks the same the other way around. A 5″ FMIC on an FBO car with upgraded turbos isn’t going to have enough cooling capacity to effectively reduce intake temps.
So we are going to go through a few scenarios here to hopefully help you decide where you fit.
Who Should Use a 5″ FMIC?
A 5″ N54 FMIC is good for cars that are FBO but running modestly low amounts of boost. Or if your car is completely stock, not running a tune, etc. If you are running map 5 on the JB4 and have a few other mods, a 5″ FMIC will work, but I would recommend sizing up to 7″, especially if you live in the South where it is hot as hell year round.
Some people will argue an FBO car with stock turbos should run a 5″ FMIC since the increased size will result in a drop in boost pressure. The increased size will likely result in like 0.2psi decrease in boost pressure, and the better cooling performance will significantly outweigh this decrease.
Who Should Use a 7″ FMIC?
N54 owners who are running FBO with a tune such as the JB4, Cobb, etc. and 15+psi of boost should use the 7″ FMIC.
If you have upgraded turbos, but the turbos are the same size as the stock turbos, ie. stage 1 or 2, then you should run a 7″ FMIC.
I’m guessing most readers here will fall into the category of a 7″ FMIC.
Who Should Use a 7.5″ or Bigger FMIC?
Only go bigger than 7″ when you have or are planning to get upgraded turbos that are stage 3+ where the size of the turbocharger is bigger than the stock turbos. If you are doing a single turbo conversion, get the 7.5″ as well.
What is the best N54 FMIC?
Our 5″ Favorites:
- VRSF 5″: for people looking for the best balance of budget and performance
- Wagner Evo II Street 5″: for people okay with spending $500
Our 7″ Favorites:
- VRSF 7″: best balance of budget and performance. This is what Zach and I are putting on our cars!
- ETS 7″: for people willing to spend for top notch
- Evolution Racewerks 7″: if you are already putting $10k into your car and an extra $1k doesn’t matter
Our 7.5″ Favorites:
- AD Engineering 1000hp: probably the best, high quality, top notch intercooler for anyone going for bigger turbos
- VRSF Stepped 7.5″: currently used in some of the record holding N54’s, great budget option
Latest posts by Jake (see all)
- How to Prevent N54 Chargepipe Failure - September 24, 2019
- BMW N54 335i Cost of Ownership – Maintenance & Repair Costs - July 11, 2019
- BMW N54 Intercooler Guide – Best N54 Intercooler - April 19, 2019