The B48 in 20i and 30i models is looking to be an excellent engine thus far. It's reliable, efficient, and sporty. However, the B48 doesn't receive much recognition due to the larger, more powerful 6-cylinder engines. That said, we're likely writing this article too soon. There is still a lot of time, development, and testing that needs to be done on B48 turbo upgrades. Nonetheless, let's jump in and discuss upgraded B48 turbos along with the risks and costs.
*B48 Pure Turbo pictured above
BMW B48 Engine Limits
Putting upper limits on stock engine internals in complex. That's especially true in the B48's case. Not enough B48 engines have explored 300+whp to know. We'll take a stab at it anyways. We know the N20 is pretty safe up to roughly 325-350 wheel torque. On paper, the B48 should be a slightly stronger engine when compared to the N20. The biggest upgrade for the B48 was the move to a closed-deck block. However, the N20 block is rarely the issue - it's the rods. BMW's B48 engine is higher compression and has a longer stroke. That may actually make life tougher on the rods.
An upgraded turbo should help shift the B48 power curve right. A larger turbo will also move a greater volume of air at a lower PSI and reduce back-pressure. All good things for engine strength. Of course, greater torque will subject the B48 to additional stress regardless.
We don't want to beat this topic to death. The point is - there are risks in heavily modding any engine and that holds true for the B48. 350+ horsepower and torque is relatively unknown territory. You can mitigate risks by ensuring you have a quality, conservative tune with proper supporting mods. Also, data-log to keep an eye on things by looking for timing pulls, lean conditions, etc.
Is Upgrading the B48 Turbo Worth It?
There's not really a right answer to this since everyone's situation is different. However, a lot of people likely do not think it's worth it which would explain why not many B48's have ventured into this territory. It could cost $5,000 to $10,000+ to get the B48 into the 350-400whp range. Then there's still the risk of blowing the motor if you don't address internals. Meanwhile, a $500 tune can get the B58 to 375-400whp which is a very safe limit for that engine. The B58 cars are more expensive up-front, but the cost of a 400whp B48 may quickly exceed the difference.
Again, everyone is in a different situation. We understand it may make sense for some people to upgrade their B48 turbo. However, equally as many would rather bite the bullet on the B58 cost up-front if performance is the end goal. All it means is development and information on the B48 is limited. That may scare even more people away from turbo upgrades on the B48. Anyways, let's move on to the exciting stuff.
BMW B48 Turbo Upgrade Options
In our past turbo guides we've gone a lot further in-depth. Unfortunately, there isn't too much info out there on the B48 turbo upgrades. As such, we'll take a simpler approach with this post. It's important you understand your power goals and know what it's going to take to get there. A lot of these turbo upgrades are also fairly modest. There really aren't too many supporting mods required. Below is what we would recommend at a minimum:
- WMI and/or E85 mix
You may consider other mods, too. Cooling often doesn't need to be addressed since the air-to-water intercooler is pretty efficient. Otherwise, the above mods should suffice for 350-400whp. Alright, let's move on to the actual B48 turbo upgrades.
1) B48 Pure Turbo Upgrade (350-375whp)
Anyone familiar with the BMW aftermarket scene has likely heard of Pure Turbo. They built some quality, well priced turbos for many of the modern turbo BMW engines. We're positive the B48 Pure Turbo will follow in those footsteps. The Pure upgrade uses the factory turbo machined to accept larger compressor and turbine wheels. Unfortunately, there isn't too much other data to go off.
Pure claims their upgraded turbo will support around 400whp. We feel that's a bit aggressive for a stock frame turbo. Will it get to 400whp with proper fueling and supporting mods? Probably. However, there's a good chance that will be pushing the turbo well outside its efficiency range. We believe the B48 Pure Turbo should be well suited to the 350-375whp range.
2) B48 BigBoost Stage 1 & 2 Turbo Upgrades (350-400whp)
Price: $2,399 (stage 1); $2,449 (stage 2)
BigBoost is a bit newer to the BMW turbo game, but they've already proven themselves worthy. They've set many records on the B58 platform with their turbo kits. For the B48, they also offer a stage 3 turbo kit that we'll reference in the next section. Rather than using the OEM turbo housing like Pure does, Big Boost actually uses Master Power turbos. These are true turbo kits rather than just an upgraded turbo. The B48 turbo kits from Big Boost include turbo inlets and outlets, a catted or catless downpipe, and oil/coolant lines.
The stage 1 offering is a 4646 turbo while the stage 2 turbo kit uses a 4949 turbo. Data is limited but we suspect the stage 1 and 2 kits will efficiently run 350whp and 400whp, respectively. There may be a bit more power on tap with appropriate fueling and supporting mods.
3) B48 BigBoost Stage 3 Turbo Upgrade (400+whp)
This is basically the same turbo kits as discussed above. You'll receive the inlets, outlets, catted or catless DP, and oil + coolant lines. However, the B48 BigBoost stage 3 turbo kit uses a 5149 turbo from Master Power. It's not much larger but the results speak for themselves.
The below dyno is a bit tough to see, but the B48 is making 513whp and 617wtq. The power is also very flat above 4250 RPM's so it's the real deal and not just a small blip in the graph. However, this was done on 33psi with a built motor running port fuel injection and E85. Needless to say - the below results aren't something everyone should expect. It's going to take money to get there. This B48 BigBoost stage 3 turbo should make 400+whp on a pretty modest setup that's realistic for most.
B48 Upgraded Turbos Summary
BMW's B48 is truly a great engine overall. It's more reliable than many of BMW's past turbo motors like the N20, N54, N55 etc. It's also a smaller, lighter weight engine compared to the inline-6 turbo motors. That keeps some weight off the front and leads to a well balanced all around car. Unfortunately, the B48 is over-shadowed by those larger engines. That means the aftermarket scene is a bit limited. We did fail to mention this yet, though. The B48 shares many components with the B58; it's basically the same engine less 2-cylinders. We believe this will help the B48 progress in the long-run.
Turbo upgrade kits are somewhat limited for the B48 at this point. Pure and BigBoost offer some excellent options for modest power goals in the 325-400whp range. However, BigBoost takes it a step further with their stage 3 B48 turbo kit. The above results speak for themselves. Even though it will take a lot of money to get a B48 to 500+whp it's still awesome to see. It goes to show there is a lot of potential for the future of the B48.
Are you looking to upgrade your B48 turbo? Drop a comment and let us know!
Looking for something modest? Check out our B48 300whp guide