This is a question that comes up often. What is the max boost the N20 stock turbo can handle? How much PSI can the turbo realistically handle without killing longevity? These are valid questions, however it's not an exact science. Regardless, in this post we will lay it out as clearly as possible.
N20 Stock Turbo Max Boost
Before we dive into the numbers there are a few things to consider. One, you likely don't want to completely max the N20 stock turbo if you're concerned about longevity. This not only applies to the turbo itself, but also the N20 engine. We wrote a post about the N20's "safe" limits here. In essence, 20-22psi is a generally accepted safe upper limit for the engine. The turbo will handle more boost, but that may also bring in concerns about turbo longevity. Anyways, the max N20 boost is as follows:
- 24-26psi max boost
- 20-22psi "safe" limit
To reiterate - this is not an exact science. There are many important factors to consider such as having proper supporting mods and a safe/conservative tune. A JB4 on map 1 and 2 will target peak boost of 20 and 21psi, respectively. That's right in the ballpark of the safe limits of the stock turbo and engine. For the adventurous crowd, the stock turbo will keep boosting up to about 24-26psi.
N20 Turbo Longevity at 20+PSI
Sticking with the trend - turbo longevity is not an exact science either. It's really challenging to put any numbers on this at all. However, there are a few general concepts we'll lay out. An N20 catless or high-flow catted downpipe will help make the turbos job a bit easier. As such, we highly recommend a DP when pushing beyond 20psi.
The harder and more frequently you use the turbos boost, the shorter lifespan. This isn't always true but turbos are a wear and tear part after all. It's fair to assume a modestly highway driven N20 turbo will hold up longer than one that's tracked and in boost often. Finally, some turbo longevity simply comes down to the luck of the draw. One N20 turbo may hold up for 50,000 miles at 23+psi. Another may give out sooner at less than 20psi.
Sorry for the vague nature of this longevity description. The primary take-away is this: the more boost applied and the more often it's used puts more stress on the turbo. That said, we believe ~20-22psi is a "safe" limit for the N20 turbo where longevity will not suffer much, if at all.
N20 Stock Turbo at Elevation
This hits home for us since we live in Colorado. As most understand - air gets thinner as elevation increases. Accordingly, the N20 turbo must work harder in order to compress the thinner air. It's an unfortunate reality for those of us at higher elevations. For example, 22psi is tougher on the turbo at 5,000 feet elevation when compared to sea level. It's a good idea to back out a few PSI at higher elevations.
However, there are positives to this too. Higher elevations often have cooler, drier air which is beneficial to performance. Turbo PSI isn't everything. If you're dying to make up for the performance loss at elevation look to other ideas. Meth injection and/or E85 mixes will help make up some lost power from running lower boost.
BMW N20 Max Boost Summary
The N20 isn't a complete beast of a performance engine. However, it's capable of making some impressive power and torque for a small 4 cylinder engine. The small single turbo is able to boost up to roughly 24-26psi. Although, that's beginning to venture towards the upper limits of the engine and the turbo. As such, we recommend sticking to roughly 20-22psi as a safe limit for the stock turbo.
To clarify, the PSI numbers we referenced were assuming sea level (or at least below ~2,000 feet elevation). Anyone at higher elevations may consider cutting out ~1-2psi to play things safe. Look to other methods such as meth and/or E85 mixes to make up the power. They're great alternatives to simply turning up boost and actually help reduce the chance of knock.
What are your experiences with the N20? Leave a comment and let us know.