An often overlooked performance upgrade on the N55 is the cooling system. When you're focused on horsepower, it doesn't seem too appealing to spend $500 on a "mod" that doesn't really produce meaning performance gains. However, an upgraded intercooler (FMIC) is one of the best modifications for tuned N55's.
Rather than being touted as a power mod, we consider an FMIC more of a reliability and efficiency mod. While the power gains might be nominal, the overall improved efficiency of the engine a decreased stress from lower air temps makes an intercooler a worthwhile longevity and reliability mod. This guide will cover the benefits of upgraded intercoolers on the N55, discuss intercooler sizing, and some of our favorite brands on the market.
N55 Upgraded Intercooler Performance Benefits
- More power / prevents loss of power
- Decreased IAT's (intake air temps)
- Improved ignition timing
- Higher boost targets
- Decreased risk of misfires/knock
Heat and it's effect on the N55
While I mentioned previously that an intercooler is not a power mod, this isn't necessarily true. An FMIC alone might add 5-10hp, but the true performance benefit comes from the consistent power it delivers and the job it does to prevent the loss of power.
Turbochargers inherently produce a ton of heat. An FMIC's job is to cool the air after it leaves the turbocharger, before it enters the combustion chamber. Heat is one of the worst elements for an engine. Heat reduces combustibility or power, but also decreases engine longevity and reliability as high temperatures over sustained periods of time can warp internals. Don't worry, not running an upgraded intercooler isn't going to lead to your internals getting warped.
But it will reduce engine efficiency and power. The OEM intercooler on the N55 is sufficient at doing what it needs to on stock engines. A stock engine doesn't push the turbocharger hard enough to overwhelm the stock FMIC. However, once you add a tune and run increased boost levels, the OEM intercooler becomes overwhelmed by the added heat being produced. This creates issues when you run the engine aggressively, doing back-to-back pulls, or sustained high RPM driving. The end result is "heat-soak".
As the OEM FMIC struggles to keep up, IAT's increase - the air is sucking in hotter air. Hotter air is less dense, or less oxidated, which results in less power. If you do back-to-back pulls on your N55, you probably notice that the car feels a little less powerful each pull. That's because of the increased IAT's caused by the stock intercooler being overwhelmed.
N55 Stock Intake Air Temps vs. Upgraded FMIC IAT's
The benefit of an upgraded intercooler is in the reduced IAT's. An intercooler will result in sustainably lower IAT's, which creates more consistent power when you are running the engine hard. It will prevent the power loss you feel when you are running back-to-back pulls.
Here is a graph of IAT's on the N55 on a 2nd to through 3rd gear pull:
On the OEM intercooler, intake air temps increase from 95 degrees to 131 degrees over the course of a 2nd through 3rd gear pull. That's an increase of 36 degrees. If you can imagine doing a pull right after this, your starting intake air temps are going to be significantly higher, which will sap power right out of the gate.
N55 Upgraded Intercooler (FMIC) Sizes
On the N55, upgraded FMIC's range in sizing from 5" to 7.5" depending on whether you have an E-Series or F-Series N55. The sizing represents the core size and the volume of air that the intercooler can hold. Generally speaking, the larger the intercooler, the more space the air has to flow-through, therefore the cooler it will be when it exits.
We'll discuss some of the different sizing ranges and help you choose what size you should opt for. But, first, lets answer a common question:
Can you go too big on an intercooler?
The short answer, yes. Choosing an intercooler that is too big for what you need it for can actually decrease performance (compared to a smaller ugpraded intercooler). Larger intercoolers have larger air volumes, which means it takes longer to fill up with air. This results in turbo lag as it takes longer for the air to get through the FMIC to the engine. Additionally, it decreases air pressure, reducing boost levels, if you aren't pushing enough air through the engine.
On stock turbochargers, you don't really have a need to go above 6" unless you are tracking your N55 frequently. Without a larger turbo, you probably aren't pushing enough air through the FMIC to justify the larger sized FMIC's, so you might experience more turbo lag and decreased boost levels.
N55 5"-6" Intercoolers
Despite these ranging on the smaller size of the spectrum, a 5" or 6" FMIC is >75% bigger than the stock intercooler. Although they are smaller than the options below, they are still considerably more capable than the OEM intercooler.
A 5" to 6" intercooler on the N55 is perfect for anyone that is FBO running a tune (JB4, MHD, etc.) and on stock turbos. It will be completely sufficient for day to day driving and for anyone who likes to get a little aggressive with the gas pedal on the streets.
A 5" or 6" intercooler is good for approx. 600whp on the N55.
Here is a graph of IAT's on an N55 with a 5" intercooler.
Go for a 5"-6" FMIC if you have stock turbo's and don't track your N55.
N55 6.5"+ FMIC Upgrades
On the E-Series, VRSF makes an intercooler up to 7.5". On the F-Series, sizing goes up to 6.5".
If you are looking to push in excess of 600whp, you are going to need an upgraded turbo. If you are going with an upgraded turbo, you should opt for the larger FMIC sizing. These FMIC's have the largest core sizes that can fit in the engine bay, creating the most cooling capacity.
If you don't plan on upgrading your turbo, a larger intercooler might still make sense if you track your N55 frequently. The turbo lag and decreased boost levels from running a large FMIC on a stock turbo isn't going to be huge, it's just not necessary to go larger if you don't need the excess capacity.
Here is a graph of an N54 (same intercooler used on the N55) with the 7.5" FMIC pushing 790whp:
N55 Upgraded FMIC Options
There are dozens of options on the market, but we're going to cover 3 of the most popular brands on the market. At the end of the day, these are all capable brands and products so it really comes down to pricing and brand preference. N55's have become a bargain market, and VRSF is our favorite options given pricing.
VRSF makes some of the best intercoolers for the price. They are probably the most popular brand on the market. They have a slew of options and sizings for the N55, although sizing options will depend on whether you have an E-Series or F-Series chassis. The F-Series cars have options for 5", 6", and 6.5". The E-Series N55's have options for 5" and 7.5".
Overall, VRSF is our top recommendation. Sizing here might be more complicated given the different sizing options, but our overall recommendation is stick to 6" or less if you aren't tracking your car or upgrading your turbos. If you can't decide on the 5" or 6" consider your power goals and also the temperatures where you live. If you are looking to push the upper bounds, say 600whp, go with the 6" option. Lastly, if you are just looking for FBO, you can stick with 5", although, maybe you live in Texas where it's 100 degrees constantly where it makes sense to go for the 6" at FBO.
Price: $400-$600 depending on size
Link: VRSF N55 Intercoolers
2) Masata Performance Intercoolers
Masata makes the best bang-for-the-buck intercoolers for UK and European folks. They have a range of intercooler sizes for both the E and F-Series N55 engines.
For E-Series N55's there is a 5" performance intercooler for those looking for a smaller yet plenty capable option. And a 7.5" Race option. The larger option is great for people who are Stage 2+ with upgraded turbos or who track their cars and need the extra cooling capacity.
For F-Series there are two 6" options as well as a 7.5" Race option as well which cover all budgets and performance goals.
Link: Masata N55 Intercoolers
3) N55 CSF Racing Intercooler
CSF's intercooler for the E-Series is a 5.5" stepped setup, and I believe 6" for the F-Series. Price wise, CSF is around the mid-point range on the market, but they have a spectacular product and reputation in the industry. CSF comes in a close second in our books, behind VRSF for the best combination of product and price.
4) N55 Wagner EVO FMIC's
Wagner Tuning is a reputable tuning company that builds excellent BMW performance products. Compared to the majority of competitors, Wagner manufacturers their products in the US. Because of this, the high quality components they use, and exceptional quality, these are high dollar and high performance units.
Wagner offers the EVO I and II for both series of N55, and even has an EVO III for the N55, which is built for 1000+whp capacities.
Price: $490 for the EVO I up to $1,090 for the EVO III
Link: Wagner Tuning N55 Intercoolers