This is a popular question asked for all the modern turbo BMW engines. The S63 powered M5 and M6 are certainly powerful cars with capable turbos. However, everything has its limits. In this post, we'll discuss the S63 stock turbo limits along with longevity and altitude effects.
S63tu Stock Turbo Max PSI
Before we give the actual numbers there are a few things to consider. Notably, you likely don't want to completely max out the S63 stock turbos. Pushing the turbos to the ragged edge (well outside of their efficiency range) may result in a short turbo life. Use your own judgement on exactly how much risk you are willing to take. All else equal, higher PSI is going to put more stress on the turbos. We also highly recommend catless downpipes for those looking to push 22+psi. In general, the max S63tu stock turbo PSI is as follows:
- ~30 PSI absolute max boost
- 24-26 PSI "safe" upper limit
This certainly is not an exact science. However, the mid 20psi range is generally seen as a relatively safe limit for the stock turbos. Once you start pushing beyond 27psi you'll notice diminishing gains. You'll still make great torque in the mid-range. However, the turbos will fall off a cliff around 5,000 RPM's and torque drops off quickly. The turbos are also operating well outside their efficiency range at 27+psi. That's going to subject the engine and turbos to higher stress and generally lead to a shorter turbo life. If you're planning to opt for upgraded turbos soon then feel free to let them rip up to 30psi. Although, that will likely push the S63tu's torque over its safe limits. A built engine is recommended to push 700+wtq.
S63tu Stock Boost
To add some color, the s63tu is programmed from the factory to run up to 22psi. However, the turbos rarely eclipse 17-18psi. The s63 targets torque values. If power and torque are down due to running at 10,000 ft elevation, for example, the turbos will use additional boost to compensate.
S63 Stock Turbos at High Elevation
Speaking of elevation - it does have a negative impact on performance due to thinner air. That also means the S63 turbos are working harder compressing thinner air. For example, standard air pressure at sea level is 14.7psi compared to 12.2psi at 5,000 ft elevation. Let's now assume two S63's are both running 25psi, one at elevation and the other at sea level:
- S63 at 5,000 feet: 25 / 12.2 = 2.05
- S63 at sea level: 25 / 14.7 = 1.70
The S63 at elevation is compressing the air to 2.05x the standard air pressure at 5,000 feet. On the other hand, at sea level the S63 is only compressing air 1.7x relative to air pressure. Point is - the turbos are working quite a bit harder at elevation. Earlier we stated 24-26psi is a safe limit for stock turbos. However, at elevation we recommend backing out 1-3psi to compensate for the thinner air.
S63 Turbo Longevity at Higher PSI
Bear with us for this vague explanation. It's just too hard to put exact numbers on longevity. We suspect stock turbo longevity will remain more or less unchanged in the 20-23psi ballpark. However, longevity may suffer when you begin pushing the turbos beyond 25psi. This is especially true as you get closer and closer to 30psi. There are other flaws to the longevity discussion, too. We're only considering peak boost and not the entire curve. Therefore, one S63 may only be running 25psi but it's trying to hold boost until redline. Another may run 28psi for a short period in the mid-range but quickly taper down to 20psi.
Then you have different drivers with different styles. How often do you actually use the boost? There really isn't an easy way to put numbers on it. Some S63 stock turbos may hold up for years to come at 27psi. Others may decide to give out at 23psi.
In general, expect reduced turbo longevity with increases in boost, especially at 25+psi. Additionally, if you're one to use the power and boost often then it's likely turbo longevity will be shorter than a modestly driven S63.
S63 Stock Turbo Max Boost Summary
The S63tu comes with capable turbochargers able to reach up to roughly 30psi. However, turbo efficiency and longevity become more concerning once pushed much beyond 25psi. A relatively safe upper limit for S63tu stock turbos is in the 24-26psi ballpark. However, altitude does have a negative impact on turbos. They have to work harder compressing thinner air, so we recommend dialing back a couple PSI at elevation.
Or leave a post and let us know about your experience with the S63 turbos