E90 FMIC BUYERS GUIDE
With several different FMIC options available for the N54 BMW's it can be difficult to decide which one is best for your build.  In this article we discuss the benefits and disadvantages of the three most popular FMIC styles for the N54, the 5", 7", and 1K (7.5").  At ARM we offer several different options so you can get the perfect FMIC paired with your build.  Here is a quick guide for appropriately sizing an FMIC for your N54 project.
 
-ARM 5" FMIC: For OEM Turbos
-ARM 7" FMIC: Excellent for OEM Turbos, Effective on Upgraded Twins
-ARM 1K (7.5") FMIC: Best Paired with Upgraded Twins or Single Turbo Setups

N54 FMIC Buyers Guide

The most common question we get regarding FMIC size is why not just get the biggest most massive intercooler available?  There are several reasons as illustrated on the chart below.  While the positive aspect of cooling performance does increase with a larger FMIC, the other three negative aspects also increase (psi drop, installation, and price).  For the moment let's assume we're willing to modify our N54's to any extent and pay any price for an FMIC to get those IAT's icy cold.  There's still the very real pressure drop that is associated with installing the 7.5" FMIC on your N54 with the stock turbos. 

n54 fmic buyers guide

An N54 with the OEM turbos targeting 20-22psi of boost may only hit 16-18psi with a 7.5" FMIC installed.  We tested this on our N54 build which previously hit over 400awhp with the ARM 7" FMIC, now only made 374awhp with the 7.5" FMIC, all due to the pressure drop.  This is a 26whp peak loss plus increased turbo lag versus the properly sized ARM 7" FMIC.  No matter how cool your IAT's get from an oversized FMIC, it will never make up for the pressure loss suffered from the larger volume.   

Now let's add to the fact that a 7.5" FMIC is more expensive and requires a bit more time to install than a 5" or 7" FMIC and you can see why it is not the ideal choice if you're planning on running the OEM turbos on your N54.  What then is the best choice for a stock turbo N54?

 
 

THE BEST FMIC FOR AN N54 ON OEM TURBOS



The best FMIC for an N54 on the stock turbos is the 7" FMIC.  Why?  It is the best balance between cooling performance and pressure drop. Despite this being a non-stepped design, the ARM 7" FMIC is measurably larger than the 5" FMIC.  While the ARM 5" FMIC comes in at 625cu.in., the ARM 7" FMIC is a significantly larger at 805cu.in.  That's 29% larger than the 5" FMIC, all without the stepped lip.  

N54 FMIC buyer's guide


On a back to back comparison between the ARM 7" FMIC and 5" FMIC, our Stage 2+ N54 test car was able to pick up an additional 10whp and 10wtq with the ARM 7" FMIC over the ARM 5" FMIC. 

5in FMIC vs 7in FMIC N54 Stage 2

As you can see peak boost comes on at exactly the same time, 2900 RPM, indicating there is no measurable difference in turbo lag between the 5" and 7" FMIC.  Add to that a higher peak hp and torque and you have a clear winner for the N54 on stock turbos.  In conclusion, your N54 will make more power with the ARM 7" FMIC over the 5" FMIC in every scenario.

The downside is that the 7" FMIC does require some trimming and it is slightly more expensive.  If neither of those aspects are an issue for you, then the 7" FMIC is the perfect intercooler for your build.  If offers the best balance between cooling performance and pressure drop on stock turbo N54 cars.  Running the 7" FMIC on a stock turbo N54, you will see close to ambient temperatures, and only approximately 1-2psi of pressure drop.


THE N54 FMIC WITH THE EASIEST INSTALLATION

If however, you are looking for a direct-fit FMIC upgrade which doesn't require trimming, the 5" FMIC is going to the be the best option for you.  It offers a substantial increase in cooling performance over the OEM intercooler and it will easily satisfy the requirement for an upgraded FMIC required by most Stage 2 tunes. 


Both the ARM 5" and 7" FMIC's are compatible with the stock intercooler piping.  However, if you want to get the most out of your ARM FMIC we strongly recommend adding the ARM Hose Upgrade. The ARM Hose Upgrade will replace the OEM intercooler piping with steel reinforced 5-layer silicone which is 50% larger, allowing more airflow for the charge air.

N54 FMIC Buyers Guide

THE BEST FMIC FOR AN N54 WITH UPGRADED TWINS OR SINGLE TURBO


If your build is going to be running upgraded twin turbos or a big single turbo kit, the best option for you is the ARM 1K (7.5") FMIC.  It will provide the best cooling performance for your setup, and with the upgraded turbos you will be able to fill the large 1,155 cubic inch core. 

Below is a datalog from our project 335xi equipped with upgraded turbos, supporting modifications, and our ARM 1K FMIC. During 3rd gear datalogs we were seeing only 5 degree increases in IAT's from the beginning of the run to the end, the starting IAT being 59 degrees Fahrenheit, and still an icy cool 64 degrees at the finish. 

Also, notice that target boost and actual boost are within 1-2psi of each other, indicating that the upgraded turbos on the N54 were able to still hit target even though they have to fill the massive 7.5" FMIC core.

N54 upgraded turbos datalog

Pairing the ARM 1K FMIC with your N54 twin turbo upgrade or single turbo kit will yield the best cooling performance without the downside of pressure drop.  If you plan on upgrading your turbos in the near future, you can get away with running the 1K FMIC on the stock turbos in the meantime to save the expense of buying two different FMIC's.  You will just need to live with some pressure loss and less power in the meantime.

SUMMING IT UP

In conclusion, there is no universal "best" FMIC for your N54, but there is a best for your N54 and what you goals are for the project.  The N54 benefits tremendously from an FMIC upgrade, much more so than the average turbocharged car, but selecting the correct FMIC for your N54 based on what you plan on doing with it is one of the more important decisions you can make for your build.  Which is why we offer 3 variations of the N54 FMIC to suit your needs.  

-ARM 5" FMIC: For OEM Turbos
-ARM 7" FMIC: Excellent for OEM Turbos, Effective on Upgraded Twins
-ARM 1K (7.5") FMIC: Best Paired with Upgraded Twins or Single Turbo Setups

If you have any questions about building your N54 feel free to reach out to us and we'll be happy to assist you with your project!

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