What is the max boost the B48 turbo can handle? How much PSI can the B48 stock turbo handle without ruining longevity? These are questions we see come up often. They're valid questions, however there is no perfect answer. Nonetheless, we'll lay it out as straight forward as possible. In this guide, we will discuss the max boost of the B48 stock turbo along with some additional factors.
BMW B48 Stock Turbo Max Boost/PSI
Before we dive into the numbers there are a few things to consider. It's typically best to avoid completely maxing the stock turbos. Too much PSI pushes them outside their efficiency range and provides diminishing gains. Additionally, there are still some unknowns regarding the B48's strength. Pushing the stock turbos too far may be nearing the upper limits of the engine.
- 22+psi max boost
- 18-19psi "safe" limit
We couldn't find any great examples of any B48 stock turbos being pushed to the absolute limit. The turbo will make 22+psi, however 18-19psi is recommended as a relatively safe limit. Of course, this limit assumes you have the proper supporting mods (downpipe, most importantly).
B48 Turbo Longevity at 18+PSI
This post may be a bit premature. There simply aren't enough B48's running 18+psi for the long-term to put perfect numbers on it. Even with data it's still a challenge. For example, the N54 limits have been well explored and documented. However, there are always the handfuls of odd cases. Some N54 turbos may hold up for years and years at 20+psi. Others let go well before that. The same idea applies to the B48, too.
We know turbo BMW's of the recent past handle tunes and additional boost pretty well. The B48 stock boost is roughly 12-13psi. We suspect the B48 turbo should not lose much longevity at 18-19psi. However, a lot of it also comes down to how hard you're pushing the turbos. It's reasonable to assume longevity of turbos used aggressively and often will suffer. That same concept applies even at stock boost.
We apologize for the vague nature of the above paragraphs. The biggest take-away is this: the more boost applied and the more frequently it's used puts more stress on the turbos. How much of an impact will that have on longevity? Only time will tell, but again we expect ~18psi to be a reasonable limit that will have minimal effects on longevity.
B48 Stock Turbo at Elevation
We're going to keep this a bit shorter than we normally would. Air gets thinner as elevation increases. Therefore, the turbos must work harder in order to compress the thinner air. It's an unfortunate reality, but 18psi is tougher on turbos at 5,000 feet elevation as compared to sea level. As such, we recommend backing out a few PSI at higher elevations.
Fortunately, higher elevations often come with the benefit of cooler air. PSI definitely is not everything. First off, colder air is denser. Secondly, colder air may enable you to run more aggressive ignition timing. Point is - play it safe and don't get too greedy at elevation. Back out a few PSI and if you're dying for extra power there are alternate ways to make some of that power back.
B48 Stock Turbo Max Boost Summary
Again, we understand and apologize that parts of this post are so vague. There simply haven't been enough B48's pushing high PSI for the long-term. As such, the rough limits are still relatively unknown. We believe ~18-19psi is a fairly safe limit for the stock B48 turbo. If you're planning to upgrade anyways then feel free to test how much boost the stock turbo can handle. Otherwise, we recommend playing it safe until the limits are more clearly understood.
An additional consideration - the B48 stock turbo must work harder to compress thinner air at elevation. We recommend backing out a few PSI. Look to make up the power with better fueling and supporting mods.
Or feel free to drop a comment and share your experience with the B48