In this guide, we discuss the N55 stock fueling limits and upgrades available. What are the limits of the N55 fuel system? At power power do N55 HPFP, LPFP, and port injection upgrades become necessary? How does E85 affect the N55 fueling limits? We'll answer these questions and then some. Additionally, we will list a few of the top fueling solutions on the market for the BMW N55 engine.
N55 Stock Fueling Limitations
Before moving into the upgrades let's talk about the limits of the stock fueling. We'll keep it pretty quick here and expand where it's helpful throughout the post. A quick note:
*Fueling limits will vary from N55 to N55 even with the same mods, boost, fuel, etc. Some of it simply comes down to the health and strength of each OE fueling component. Limits can also vary based on tuning and other factors. We don't recommend pushing the absolute limits of anything, but it's a good idea to data-log often if you're pushing the fuel limits.
That said, the first limits you'll reach with the N55 fueling are typically around:
- Pump gas: 425-475whp
- E30: 350-400whp
On pump gas the N55 stock turbo will run out of breathing room well before the fueling. However, E30 fuel will quickly reach the limits even with the stock turbo. A high-pressure fuel pump becomes a necessary mod above E30 fueling, especially with a turbo upgrade.
N55 Water Methanol Injection
We're not really going to discuss WMI in this article. We will write a separate guide for N55 methanol injection. However, WMI does act as additional fueling. HPFP or port injection mods can get expensive for the N55 engine. As such, water-methanol injection is a solid option for those with modest goals. Depending on how much you want to lean on methanol injection the N55 can make 500+whp with stock fueling.
You'll still be stuck with pump gas or E30 mixtures at the most. However, WMI remains a good solution for modest setups. Again, we'll expand on this in another post and link to it here.
Building In Some Headroom
If you're modding your fuel system it's always a good idea to build in some headroom. The more the merrier, but having 10-15% breathing room will help ensure a reliable setup. This doesn't just apply to fueling.
If you want a 700whp N55 and you're building the motor you probably don't build it to handle exactly 700whp.
1) N55 Upgraded High-Pressure Fuel Pump (HPFP)
Those familiar with the N54 understand the LPFP is typically the first limitation. However, on the N55 the HPFP is the first part of the fueling system to max out. It's one of the bigger flaws with the N55, in our opinion. HPFP upgrades aren't cheap. There are ways around it like port injection, but that's not much cheaper. We'll also discuss other less expensive options like charge pipe or throttle body injection.
Anyways, back to the N55 HPFP discussion. There are a few pros and cons to opting for high-pressure fuel pump upgrades:
N55 HPFP Upgrade Pros:
- Simple setup
- Direct injection remains only fueling
HPFP upgrades are typically plug and play solutions. Install isn't overly complicated, but it can take some time. Most importantly, direct injection is a superior method of fueling. It's more accurate than port or charge pipe injection since a very precise amount of fuel is sprayed directly into the cylinders.
N55 HPFP Upgrade Cons:
- Most upgrades are only for 2013+ N55's
- Not as capable as port injection
HPFP upgrades often run north of $1,000. Common upgrades like the Dorch Engineering HPFP only fit 2013+ N55 engines with the OE Bosch pump. All of that cost and these setups still don't offer the same capability as port injection.
N55 HPFP Upgrade Options
Below we'll list a few of our favorite upgrades available for the N55. This isn't an exhaustive list by any means. There are quite a few choices around. However, the below list includes some HPFP upgrades that we believe offer the best balance of price, quality, and proven results.
1. Dorch Engineering N55 Stage 1 & 2 HPFP
Dorch products are well-known when it comes to N55 fueling solutions. However, they only offer products for 2013+ N55 engines. The stage 1 kit comes in at $1,199 and is able to support roughly 550whp. However, if you're trying to run heavy E85 mixtures you'll probably cap this stage 1 Dorch HPFP well before 550whp.
Stage 2 HPFP solutions from Dorch come in at $1,699 so it's not cheap. However, these pumps are good for up to about 650whp or 500whp on 100% E85. It's a solid amount of power for 100% E85 with direct injection only. However, the stage 2 pump is pretty expensive and the upper limits are much lower than with port injection.
Price: $1,199 - $1,699
HP Supported: ~450-650whp
2. Tuning Tech FS (TTFS)/XDI N55 HPFP
TTFS offers another popular HPFP solution for the N55. It comes it at $1,695 and offers performance similar to the Dorch Stage 1 HPFP. As such, it's a little more expensive for the performance. Nonetheless, it remains a solid solution for N55 owners looking to go the HPFP upgrade route.
HP Supported: ~450-550whp
3. Nostrum N55 HPFP Kit
We're not familiar with Nostrum and this appears to be a brand new offering as of the last few months. Unfortunately, there isn't much data around. However, Nostrum claims this pump will fit any N55 models as a direct fit. They also claim it can support about 63% more flow compared to the stock pump. That puts the Nostrum HPFP right in the same ballpark of the Dorch Stage 2. Pricing is similar at $1,650.
We would be interested to see some more results on this before we say this would be our top option. It's definitely a promising development given they claim it fits all N55 models.
HP Supported: 550-650whp
2) N55 Charge Pipe Injection Fueling Mods
Charge pipe injection (CPI) is a very similar concept to methanol injection. Of course, instead of injecting a water-methanol mix into the charge pipe you're injecting fuel. These kits cannot be run in conjunction with standard CP WMI kits. N55 CPI isn't a great solution for those looking to make huge power. However, if you just need a little extra fuel flow it's a great option. A few pros and cons to N55 CP injection include:
N55 CPI Pros
- Relatively simple setup
Charge pipe injection is a lot less expensive than an N55 HPFP upgrade or port injection. It's also a pretty simple setup as you're just running a 7th fuel injector directly into the charge pipe meth bungs. Of course, you do need a controller and fueling lines.
N55 Charge Pipe Injection Cons
- Limited fuel flow
- Cannot be combined with WMI
- Uneven fuel flow
CPI isn't going to provide nearly the same flow as PI or HPFP upgrades. Meth kits also utilize the charge pipe bungs, so you won't be able to run WMI and CPI. You could combine the two but that would require moving one of the injection methods to port. Such as port fuel injection or port methanol injection. Also, this concern is shared with meth kits that spray in the charge pipe. Not all cylinders will always receive equal flow. That can increase risk if one cylinder is running shorter on fuel.
Best N55 Charge Pipe Injection Kits
We'll keep this quick since the go to option for charge pipe injection is Fuel-It! You can find their CPI starter kit here. By the time everything is optioned out with the injector controller you're looking at about $600-700. That also doesn't include the charge pipe. However, most looking for fueling mods are probably already running an aftermarket charge pipe anyways.
Exact power supported depends greatly on tuning and specific E85 mix. You'll probably pick up an extra 10-15% fuel flow capabilities. As such, if you're maxing your stock fueling at 400whp then CPI will get you into the 440-450whp ballpark.
3) N55 Port Injection (PI) Fueling
Last but not least - N55 port injection. This is the highly tested, proven fueling method to push the N55 to its limits. Port injection adds an additional fuel rail and 6 more fuel injectors. These systems are run off the N55's LPFP, so that's another part you'll likely need to upgrade. PI is expensive, but can easily support 600-700+whp on 100% E85. It all depends how everything is optioned out, of course. However, the point remains - port injection is the ultimate N55 fueling solution.
N55 PI Pros:
- Can support 700+whp
There may be other pros to port injection, but this is obviously the big one. If you're looking for a modest 400-550whp setup on E85 then you'll probably find HPFP upgrades the superior option. We like the idea of making power solely on direct injection, if possible. However, N55 port injection offers a lot more fuel flow than just about any HPFP solution on the market. Port injectors can also be upgraded down the road if you're looking for more power.
N55 PI Cons:
- More complex setup
- More parts to fail
Depending on options, port injection can easily run in the ballpark of $1,500-3,000. You'll also need a LPFP upgrade so add that expense in. Controlling an extra fuel rail and 6 more injectors obviously makes things a bit more complex. It's important to have everything well setup and well controlled by your tune. Fortunately, port injectors are pretty inexpensive. However, N55 PI still adds a few more parts that may potentially fail. It's definitely a more complex and involving setup over HPFP upgrades or CPI.
Best N55 PI Options
We'll keep this pretty short, too. Port injection is a cheap fueling upgrade for the N55. As such, we recommend doing some research and finding the kit that best meets your budget and goals. We really like the options from Fuel-It, but there are other great options out there. Note - the previous link goes to the F-series N55 PI so ensure you verify fitment and purchase the correct port injection kit.
BMW N55 Fueling Mods Summary
The N55 is a solid engine, overall. However, fueling is definitely one of the bigger shortcoming of the N55 engine. The HPFP's aren't quite as capable compared to engines like the N54, S55, B58, etc. Fortunately, the stock fueling is still pretty capable especially with a WMI or CPI setup. Those looking to make the power on heavy E85 mixes will need to consider solutions like port injection or HPFP upgrades.
There are some great HPFP options that can make 500+whp on 100% E85, and even more power on lower mixes. We also like the idea of making power on direct injection since it does have the accuracy advantage over PI. Nonetheless, port injection is a tried and proven method to make big power on the N55. Port injection is able to support 500-700+whp on full E85.
What's your experience with N55 fueling? What fueling mods are you currently running or considering?