We're following up our S55 twin turbo upgrade guide with a similar article for single turbo kits. Many BMW enthusiasts are familiar with the S55 M3 & M4's accomplishments. It didn't take much time for the S55 to break into the 600whp ballpark on stock turbos. A few years later, RK Tunes broke the 1000whp mark on a single turbo kit. That's probably more power than most M3 & M4 owners care to have. However, it goes to show the potential of S55 single turbo upgrades. In this article, we discuss a few of the best S55 M3/M4 ST kits along with the power, risks, and costs.
*S55 M2C, M3, M4 Doc Race Single Turbo Kit pictured above
BMW S55 Engine Limits
Of course, any major power upgrades come with the concern of pushing the engine near and beyond its limit. The S55 is a fairly strong motor, but it's also far from indestructible. 650 wheel torque is generally a safe limit for the M2, M3, and M4 engine. However, there are tons of factors that play a role in the upper limits of the S55 engine. You might be able to get away with more torque in the long run while other engines may let go at 650 torque.
Point is - there are some unknowns when you upgrade the S55 turbos and begin pushing towards the limits. Nonetheless, all else equal, pushing more boost and power increases the chance of blowing the engine. It's a risk everyone should understand before pushing the engine too far. Some may be willing to take that risk while others may consider building the S55 engine up-front. We'll expand on this a bit throughout the article.
S55 Single Turbo Benefits
We're mostly focusing on benefits to engine safety here. A few benefits to opting for a single turbo kit instead of twin turbos include:
- Less low-end torque
- Shift power curve right
- Slower spool
We wrote about these concepts in the twin turbo guide here. A large single turbo is generally going to spool a little slower and have a higher boost threshold. Reducing low-end torque is actually safer for the engine. This is because the S55's pistons are moving slower at lower RPM's. That subjects the engine to high cylinder pressures for a longer period which increases the risk of pre-detonation. Additionally, a large single turbo will make more power on the top-end compared to smaller twin turbo options.
Single vs Twin Turbo M2, M3, M4
We're writing this post to hopefully get readers started on learning about what turbo set-up is right for them. There is no single answer that's correct for everyone. As such, take this with a grain of salt. However, we really don't like single turbo kits on the BMW S55 engine. There are plenty of twin turbo options to support 600-850whp. A few twin turbo upgrades are even capable of 1000+whp.
We haven't seen enough evidence that there's a big enough benefit to justify converting the S55 M2, M3, or M4 to a single turbo. The twin turbos are just too capable and can support the goals for just about anyone. It's also a much simpler set-up to install and get up and running with twins.
That said, we do LOVE the sound of the single turbos. Not many top mount kits exist, but there are some benefits to running a top mount single turbo. It makes turbo servicing and maintenance easier down the road. It's also easy to install a new top mount turbo should you want to upgrade for more power or go smaller for quicker spool.
S55 Single Turbo Upgrades
With that info out of the way, let's move onto the more exciting stuff. We will break down the S55 single turbo kits by the following power levels:
A few quick notes about picking the right turbo. Most of the horsepower numbers we quote assume you're running E50+ fueling and/or methanol injection. It will take a lot more turbo to hit X power without ethanol, race gas, and/or meth. We also recommend keeping turbo set-ups within their efficiency range. Understand a goal and pick the appropriate turbo kit. For example, if you plan to push 750whp you shouldn't choose a turbo that's completely maxed out at 750whp.
Build in a little bit of headroom, but don't get too excessive. You don't want to introduce unnecessary lag with a 1000whp capable turbo if you don't plan on pushing more than 750whp. This is just some basic stuff to consider before pulling the trigger on an S55 single turbo upgrade. Know your goals and choose an option that allows a little breathing room.
BMW S55 700-850WHP Single Turbos
Turbos we mention in this section can certainly be turned down to make under the 700whp mark. However, most opting for a single turbo conversion are likely shooting for at least close to the 700whp or more. Nonetheless, we'll consider these some of the "modest" single turbo options for the S55 M2, M3, and M4. With proper tuning and fueling you can get away with these modest setups on a stock S55 engine. Supporting mods are also quite a bit less demanding than those required for 850+whp. However, between the turbo kit and mods these set-ups can still easily run into the $8,000 to $15,000+ range.
Supporting Mods for 700-850WHP
- Heat exchanger & intercooler
- Port injection with E50+ fuel
- Clutch upgrade (for DCT)
- Crank hub
Those looking to stick on the lower end of the power goals may be able to skip the port injection and clutch upgrades. DCT clutches are known to start slipping around 650-675wtq on the S55. Lower E85 mixes with methanol injection may not require port injection. However, we're big fans of E85 and highly recommend opting for port injection and at least E50 fueling. Otherwise, cooling mods and the crank hub are two areas that should be addressed before upgrading to a large single turbo.
Below we'll quickly discuss a couple of our favorite S55 turbos for those looking to make roughly 700-850whp. This is far from an exhaustive list and plenty of other solid options exist. These are just a few S55 single turbo kits that we believe offer a solid balance of price, quality, and performance.
1) DOC Race S55 Single Turbo Kit (750-875whp)
Price: $6,995 - 7,595
We're big fans of Doc Race and the single turbo kits they make. They're a popular choice in the BMW world and it's hard to go wrong with the high quality Precision Turbos they use. Doc Race will make another appearance in the next section when we discuss 850+whp setups. For now we'll focus on their S55 kits with some of the smaller single turbos - the PT 6266, 6466, and 6766. These are high quality turbo kits with excellent turbos to match, but they're also on the pricier side.
Doc Race kits use the more expensive ball bearing turbos, which offer superior spool to journal bearings. With proper tuning the 6266 and 6466 actually spool pretty well on the BMW S55 engine. Of course, don't expect the same response as stock turbos or smaller upgraded twins. Nonetheless, the PT 6266, 6466, and 6766 are great options to push the S55 into the 700-850whp area. The only thing we don't like about this turbo option is that it's a bottom mount kit.
2) Big Boost S55 Turbo Upgrade (750-900+whp)
Big Boost is another company well known in the BMW world for their single turbo kits. They did some excellent work on the B58 and were the first to set many power records on that platform. Their S55 single turbo kit is also a great looking option. While DOC uses Precision Turbos, Big Boost opts for turbos from Master Power. They also use ceramic ball bearing turbos that offer quicker spool.
Big Boost offers 3 different turbo choices for the BMW S55 M2, M3, and M4. Choose between the 6564 good for 820whp, 6766 good for 900whp, or the 6967 that can make up to 1000whp. This another bottom mount turbo kit, which is our biggest gripe with many of the S55 single turbo kits.
3) JPWorkz S55 Single Turbo Kit (700-800whp)
Price: $5,599 - 5,799
It's a breath of fresh air to finally include a top mount kit for the S55 engine. We're not familiar with the company and these turbo kits, but it's surely worth a mention as one of the few top mounts available. JPWorkz offers Precision Turbos but the only two standard options are the PT 6266 and 6466. They're both twin scroll gen 2 ball bearing options as with the DOC Race kits.
The 6266 turbo should be good for up to 750whp while the 6466 will support roughly 800-825whp. However, there may be some flexibility with these kits. If you want more power you may be able to work with JPWorkz to get the kit without a turbo. You could then source the turbo of your choice to bolt up. That's the excellent thing about top mount kits. It's easy to swap turbos or replace the turbo if it fails. Top mount single turbos also look and sound beautiful on the S55 M2, M3, & M4.
BMW S55 850+WHP Turbo Kits
Many of these setups aren't for the faint of heart. These S55 turbos will certainly have the ability to push the motor well beyond its safe limits. This is getting into the territory where a built motor is a necessity. The list of supporting mods also gets a lot deeper with many other upgrades that are a good idea to knock out. Shooting for a reliable, safe 850+whp BMW S55 can easily run in excess of $20,000 all in.
Supporting Mods for 850+WHP
- Full bolt-ons
- Crank hub
- Port injection
- DCT clutch packs
- Built engine
- Extensive tuning
We're surely missing a few things that some may consider upgrading. However, the list runs pretty deep as is. You'll want all the basic bolt-ons and cooling mods. Fueling mods for 100% E85 are a good idea and DCT upgrades become necessary. You could snap an M2, M3, or M4 axle with this kind of power so that's another good mod. Proper wheels and tires to put the power down. If you choose to not build the S55 engine then it's no longer a matter of if it blows up - it's when. Finally, it will take some extensive tuning work to dial the car in.
All of this stuff adds up to considerable amounts of money. You'll also need a lot of knowledge or will need to rely on others with the knowledge to get these 850+whp setups running well. Anyways, for those willing to commit below are a few of your options to make ridiculous amounts of power with the BMW S55.
1) DOC Race S55 Turbo Upgrades (950-1200+whp)
Price: $7,795 - 7,995
Well, we said Doc Race would make another appearance in this section. Here it is with the same turbo kit as we discussed above just with the larger turbo options. They're all ball bearing twin scroll turbos from Precision Turbo. The 6870 turbo will help boost the S55 into the 900whp territory. Those looking to break 1000whp should consider the even larger 7275 turbo.
Then again, if you're going that far you might as well go for the 7675 turbo and shoot for the 1200whp mark. It's a stupid amount of power and you'll certainly need some head work done to help support that air-flow on the high end. It's also pushing into dyno queen territory as putting down 1000+whp on the M2, M3, or M4 is not easy. Of course, these high power setups also trade off a lot of spool in favor of big top-end power. You'll need a lot of RPM's to get these turbos at full boost.
2) S55 Custom Turbo Kits (1000-1200+whp)
We could have dropped Big Boost down here since they do have a few options to eclipse 850whp. However, instead we'll take the time to write generically about custom setup options. You may be able to custom machine a top or bottom mount turbo kit yourself. Otherwise, you can buy an existing turbo kit and swap in the turbo of your choice.
For example, the JPWorkz top mount kit only comes standard with a 6266 or 6466 turbo. However, once the manifold and conversion is in place you can pop any turbo up there. Fitment may take some work but you could in theory bolt up a Precision PT8385 turbo. Will the S55 even be able to spool a turbo of that size without extensive internal work, tuning, etc? Maybe not. This is unknown territory, but the options with single turbos are endless.
BMW S55 Single Turbo Upgrade Summary
Single turbo kits certainly have the ability to push the M2, M3, and M4 into ridiculous territory. Plenty of options exist for those looking to make 700-1000+whp. However, these setups can get pretty costly especially if you plan to push much beyond the S55's 650wtq "safe" limit. Single turbo conversions are popular on the N54 engine, but they don't get quite the same hype on the S55.
Part of it is likely due to the fact the S55 can already make 600whp on the stock turbos and north of 1000whp with twin turbo upgrades. Each to their own, but it's a big reason we're not fans on single turbos on the M2, M3, or M4. We much prefer the twin turbo idea, but the S55 does make some awesome sounds with a large single turbo.
Those committed to the single turbo route have plenty of choices out there. DOC Race makes some great S55 single turbo kits that can support 700-1200whp. We also like the Big Boost options a lot for those looking for 700-1000whp. Otherwise, JPWorkz turbo kits aren't quite as capable as sold but the top mount kit is certainly tempting. Choose the option that best suits your goals and budget and have some fun!
Do you have a single turbo S55 or are you considering going single turbo?
Drop a comment and let us know. Or scroll down to check out some more BMW S55 content