How Much Boost can the N54 Stock Twin Turbos Handle?
Even today, we see this question asked all too often along with many conflicting responses. We’ll keep this post rather short and straight to the point. However, the answer does depend upon each persons goals and plans for their N54. What is the max boost you should run on your N54 stock turbos?
N54 Max Boost For Turbo Longevity
- 17-18psi – stock inlets/outlets
- 19-20psi – upgraded inlets/outlets
N54 Max Boost No Longevity Concerns
- ~20-22psi – stock inlets/outlets
- ~23-25psi upgraded inlets/outlets
*Assuming car is FBO with catless downpipes.
*20-21+psi requires upgraded TMAP
Why Inlets & Outlets Matter on N54
It should be noted up front – inlets are more beneficial than outlets on the N54. However, inlets & outlets together will have the most notable benefits. Both stock location and relocated will have similar results on stock turbos.
PSI or boost is not the only measure for turbos. As some may understand, an N54 with a large 6466 single turbo will make more power at 20psi compared to stock turbos at 20psi. This is because the large single turbo has a higher CFM flow (cubic/feet per minute). It simply flows more air. Upgraded inlets and outlets work in more or less the same way.
Inlets/outlets help flow a greater volume of air through the stock turbos. Turbo efficiency increases and WGDC decreases. In short, this helps reduce the work required by the turbos at a given PSI. They also allow for slightly more peak boost and more boost in the higher RPMs. Some argue upgraded inlets and outlets are not worth it on stock turbo N54’s. However, they do assist with longevity when pushing stock turbos towards the limit.
Altitude Effects on N54 Turbos
Generally, turbos must work harder at higher elevation as they are tasked with compressing thinner air. Standard atmospheric pressure at sea level is 14.7psi. Compare that to 12.2psi at 5000 feet elevation, for example. Now lets compare an N54 running 18psi at sea level and 5000 feet.
- N54 at Sea Level: 18 / 14.7 = 1.22
- N54 at 5000 Feet: 18 / 12.2 = 1.47
To avoid confusion, boost is measured as pressure (psi) above standard air pressure. However, at elevation the turbos are breathing thinner air. At sea level the N54’s turbos are only compressing the air 1.22x ambient air pressure. At the same 18psi, at 5000 feet elevation, the turbos are compressing air to 1.47x ambient air pressure. Long story short – the turbos are working quite a bit harder at elevation.
Does altitude really matter that much?
*Story in Colorado. N54 driven frequently at 5000-7000 feet elevation. Occasional 7000-10,000+ feet elevation.
Well, take this story for what it’s worth and it’s the short version. Our N54 335i received new OEM turbos right around 82,000 miles under the extended warranty for waste-gate rattle. The original turbos ran well and were pushed to 17-17.5psi peak. With the new turbos, still on stock inlets and outlets, we decided to turn boost up to about 19psi peak. Blew the bank 2 turbo within 1,000 miles. BMW replaced again, for free. We blew the turbos for a second time within a few thousand miles at 19psi. Once again, BMW replaced for free but they made it clear it was the last time. They were aware the N54 was modded and came to the conclusion the bank 2 turbo was over-spun both times.
As such, we kept boost to 17.5psi peak and never had any more issues. Turbos now have about 30,000 miles on them. We installed inlets and outlets a few months ago and have been pushing 18.5psi since, without issues. We should also note – there may have been other factors at play with the blown turbos, but it’s too hard to say indefinitely.
N54 Stock Turbos Max Boost Summary
There is no definitive answer to exactly how long stock turbos will last at any given boost. Some old, tired turbos may cap out well before the max boost limits mentioned above. Other old turbos may gladly hold up for years at 20psi. Likewise, newer OEM turbos may decide to give out before 20psi.
However, if you are concerned about N54 turbo longevity, somewhere in the ballpark of 17-18psi on stock inlets/outlets and 19-20psi on upgraded should be safe for most. For those with plans to upgrade in the near future, feel free to have some fun and max out the N54’s stock turbos. Although, maxing the turbos is pushing them outside of their efficiency range. You may be risking damage for minimal performance gains.
Hi,
Very interesting, and well written article. Straight to point, clear and concise.
I just finished a FOB install that included upgraded inlets, outlets, FMIC, down pipes and charge pipe. And new Vargas OEM turbo replacement with the billet compressor.
The logs show 12.5 psi boost on stock setting (JB4 map 0) . It should be 8 psi, max! For whatever reason, the boost is higher than advertised on all the JB4 settings. On Map 3, with meth, the advertised boost should be 14-15, yet the logs show high 16 to mid 17 psi. And I verified these logs with another logging device. Yep, the boost is higher than advertised. This was a curiosity, which lead me to your article.
I’m a bit new to turbo charging. so my novice question is;
Can upgraded inlets, outlets, catless downpipes, FMIC and charge pipe be the culprit for boost PSI level being higher than advertised?
Thanks!
Hi Mike,
Congrats on the upgrades. Interesting – that sounds like quite a bit of overboost. I am not quite as familiar with map 3 as I don’t run meth, but I believe you set the boost target when setting up the meth injection map. Did you run any data logs to check what the actual target boost is?
Additionally, you may try resetting adaptations on the JB4. It may be taking some time for everything to adapt and adjust to the newfound air-flow with DP’s, inlets, billet wheel, etc. Also, with your mods you might want to consider running a back-end flash map. If you get a data-log you’re welcome to e-mail that to [email protected] and we may be able to assist. N54tech is also a good resource for support as the forum is run by the Burger Motorsports crew (JB4).
Best Regards,
BMWTuning
Hi,
Thanks for the nice reply. A good advice. I am chatting with BMS and they have a copy of my recent logs. They provided about half of the upgrades, most importantly the JB4.
Yep, I confirmed the Map 3 boost is running a little high, and suspect BMS will have some good advice.
Thanks!
Mike
Hello, i had a question. First of all , thank you for the excellent article. Im in need of new turbos. More than likely going stock turbos and i intend to go FBO (inlets/outlets,FMIC,) but as far as the downpipes. I am considering going with a hi-flow catted downpipes. In your opinion, what would you say are fun but reliable numbers(psi) and what would be pushing it? Thanks in advance.
Hi Adrian,
It’s always hard to say with certainty. Some N54 stock turbos hold up for years at 20+psi, and others might give out within a few years even with a modest 15psi. The risk is always there when upping the boost on stock turbos. Anyways, I’d say 15-17psi is a good range to stick with if you want to keep longevity. Ensure no boost leaks or other issues that may kill the turbos sooner.
There are also some solid upgraded turbo options in the sub $2000 price range. Something like RB OEM billets aren’t going to offer huge power benefits, but they should offer improved reliability at higher than stock boost. Those come in around $1,250.
Then there are the RB ones at $1,700, which will offer a great performance increase. The turbos are quoted as good for 425-475whp goals, which is very conservative depending on mods, fueling, etc. They’re way more capable than stock, but RB quotes power levels within efficiency ranges. The stock turbos will be working a lot harder, generating more heat, and require more boost to hit similar numbers.
If you’re willing to stretch the budget then RB twos or Twos plus are great options. We run RB Twos Plus on our 335i, and have nothing bad to say about them. They’re a little bit slower to spool compared to stock, but still very quick and power through the whole rev range is amazing. Awesome turbos for a very fair price. However, to fully utilize them you’re looking at a 7″ FMIC, DPs, inlets & outlets, fueling mods and/or methanol injection, etc. In other words, if you’re not interested in a solid 500+whp setup then the RB OEM billets or RB ones are great alternatives to OEM turbos.
Best Regards,
Zach