Upgrading the N54 turbos isn’t a decision that most of us take lightly. It can be a serious financial commitment, and you want the money to feel like it was well spent. I know I personally spent a couple weeks deciding between N54 single vs twin turbo upgrades. Once I decided on twins, I then spent another couple weeks deciding which upgraded twins to move forward with.
Jake and I both own N54’s with turbo upgrades, so I am very familiar with the process of deciding on the right turbo upgrades (the extensive research and writing I’ve done on N54 single vs twin turbo upgrades also helps). Ultimately, deciding on the right setup for your goals & budget can be a time consuming, exhaustive process.
Worry not, though. In this guide, I discuss the differences between N54 single vs twin turbos alongside important considerations before choosing which turbo setup is best for you.
N54 ST vs TT Considerations
- Power goals
- Powerband / low-end vs high-end / spool
- Maintenance & Reliability
This list isn’t in any particular order (nor is it totally exhaustive as this can be subjective), but these are some of the important things to consider before choosing between twins or a single turbo. What are your N54 power goals and how do the turbo setups meet them? How do N54 single vs twin turbo upgrades compare with the powerband, low-end vs high-end power & torque, spool, and boost threshold?
What about cost, maintenance, and reliability? Let’s jump in, answer all these questions, and discuss more about N54 single vs twin turbo upgrades.
1) N54 Turbo Upgrade Power Goals
Starting off with one of the most important topics – what are your N54 power goals? There are excellent single turbo setups that can support 500-1,000+whp. Twin turbo upgrades can support anything from roughly 450-700whp. Yes, some TT’s can and have made 750+whp. However, they’re few and far between.
That’s in part due to the fact many people believe the N54 is simply better suited to a big single turbo at 700+whp. And I totally agree with that based on my experience with N54 turbo upgrades. Ultimately, if your goals are 700+whp I would recommend just crossing twin turbos off the list right away.
At the end, I’ll circle back with recommendations on which setup to choose based on power goals. It may fit in this section, but it’s easier to discuss once we move thru the rest of the ST vs TT considerations.
2) ST vs TT Powerband, Lag, Spool, Etc.
This is another major topic when it comes to single turbo vs twin turbo setups, and there are a lot of individual pieces to dive into here. A couple factors to consider include:
- Twin turbos offer better spool, a lower boost threshold, and more low-end torque
- Single turbos deliver better mid-range and top-end power
- Single turbos are easier on the engine at a given power level
Now, these are generalities and don’t necessarily apply to every single vs twin turbo setup. For example, a small single turbo like a PT5558 will likely deliver similar spool to RB Game Finishers (or any other true TD-04 twin setup). Meanwhile, the RB Game Finisher’s will deliver better better peak and top-end power.
Nonetheless, these general rules apply to most setups. TD-03 twin turbos built for 550whp are going to spool faster and deliver more low-end torque than any single turbo. TD-04’s will spool better than most single turbos, but won’t deliver as much peak or top-end power.
Ultimately, the main takeaway is that larger, more capable turbos are going to have more lag, a higher boost threshold, and less low-end torque. You’re trading off those factors for better peak and top-end power.
If you want an OEM-like feel then TD-03 stock frame turbos are going to be your best bet, but they’re capped around 550-575whp. If you want big power then TD-04 twins or a big single will deliver, but you’re sacrificing some spool and low-end. Now, the most important topic is for those planning to run stock engines without any internal upgrades.
A Single Turbo is Easier on the Engine
Larger turbos shift the power curve to the right. Again, you have less low-end torque, more lag, and a higher boost threshold. Let’s look at a couple dynos quickly.
*Image from this forum thread (also check out Jake Spence on YT; he has some great content)
This is a Precision 6266 (PT6266) turbo making 749whp at 29psi. A closer look shows roughly 300wtq at 3,000rpm, 420wtq at 3,500, and 540wtq at 4k. Peak power occurs at the very top-end of the dyno run. Now, let’s look at a twin turbo dyno (true TD-04’s for a somewhat similar example).
The above dyno shows RB Game Finisher High-Flow 19T turbos at 27psi. These are true TD-04 twin turbos, so this isn’t an extreme comparison with the previous PT6266. Here, we see roughly 375wtq at 3k rpm, 525wtq at 3,500, and 590wtq at 4k. The dyno also starts at 2,600rpm (vs about 2,100 for the 6266 single), so the torque numbers would maybe even be a tad higher given another 500+rpm to start spooling.
Why is the ST easier on the engine?
Torque – that’s the simple one word answer. However, there are really a few things at play here. A large single turbo can make higher peak power with less boost and less torque. Boost and torque put more stress on the engine than horsepower.
Torque is the ability to do work while power is simply the rate at which work is done. In essence, torque tells you how forcefully the pistons are driven downwards in order to create the twisting force. But isn’t the single turbo above making more torque?
Yes, but let’s look at 6,500rpm. The single turbo is making 749whp at just over 600wtq. On the other hand, the twins are rapidly dropping torque by that point. They dip to 600wtq around 5,900rpm where they’re making about 670whp. If you tuned both of these to make 600wtq peak, then the ST is making about 740whp whereas the twins would be making around 670whp. That’s 70whp extra at similar boost and torque.
More importantly is the rate at which the twin turbos pour on torque and boost on the lower-end. Lower engine speed means the pistons are moving slower and the cylinders are firing slower. That subjects the cylinders to high pressures and heat for longer periods, which increases the chance of engine knock.
Ultimately, shifting the power curve right leads to more power with less peak torque. It also helps avoid the danger of making too much torque too quickly in the lower RPM’s. I should also note – both the above dynos are on stock engines and pushing beyond the limits for longevity and reliability. On a stock engine, the max recommended power levels recommended are:
- TD-03 twins: 550-600whp
- TD-04 twins: 600-650whp
- Single turbo: 650-700whp (for a 6266, 6466, or equivalent size)
3) N54 Single vs Twin Turbo Costs
Alright, that portion took a little bit to cover, but I promise these next topics are much quicker. Twin turbos are less expensive than single turbo conversions. Costs for turbo kits – not including bolt-ons or other recommended supporting mods – are generally about:
- Singles: $3,500 to $7,000
- Twins: $1,500 to $3,500
The starting price of single turbo conversions is about the top-end of what you’ll pay for twin turbos. However, single turbos include a downpipe, filter, and don’t require inlets or outlets. Twin turbos don’t include those items by default as they’re OEM fitment.
Inlets & outlets may not be required, but they are highly recommended. This is a moot point if you already have the bolt-ons anyway. However, if you’re starting with a clean slate then it’s about $1,000 in extra mods for twin turbos. That can bring the prices pretty close if you’re looking at something like a SpeedTech PT Gen2 top-mount kit (~$3,800-4,500) versus RB GF High Flow (~$4,200-4,500 once factoring inlets, outlets, intakes, and downpipes).
That said, there are also some additional factors with single turbos like the PCV system, MAC solenoid, etc. that can add some extra costs too. Additionally, you can get quality twin turbo kits for under $2,000 – much cheaper than you’re going to find any quality ST kit. Ultimately, twin turbo upgrades are the cheaper route.
4) Maintenance & Reliability
Back in the day, N54 twin turbo upgrades weren’t always reliable. It makes sense since a lot of the turbo upgrades were from newer companies. There were kinks to work out, lessons to learn, etc. However, the twin turbos now days (from companies like RB, Vargas, Pure, etc.) offer good reliability.
Single turbos are every bit as reliable – if not more so – than twin turbos. Most single turbos come from major manufacturers like Precision, Garrett, and BorgWarner. Turbo reliability isn’t the only point here, though.
Top-mount single turbo kits are the real topic, and it’s a clear win for them. If a top-mount ST fails, it’s a few bolts and you can drop a new turbo on in a matter of minutes. Twin turbos or bottom mount singles? You’re dropping the subframe and spending another 8-15+ hours for replacement.
Plus, if you ever decide you want to upgrade turbos then the single is, once again, as easy as a few bolts. With the twins, you have to factor in your own time or the $800-1,500+ a repair shop is going to charge for install.
5) N54 Single vs Twin Turbo Sounds
Of course, sounds are very subjective so I’ll be equally as quick. In my opinion – and I believe most will agree – single turbo N54’s sound better. I think my twin turbo N54 sounds great, and I personally don’t care about sounds too much (so it wasn’t really a factor in my decision). However, I have to give it to single turbo N54’s; they sound pretty badass.
Ultimate Recommendation By Power Goals
With all that out of the way here’s my ultimate recommendation on turbo setups by power goals:
- Under 550whp: Twins
- 550-650whp: Either
- Over 650whp: Single
In my opinion, the N54 is best suited to twin turbos under the 550whp mark. Stock-frame turbos can hit these numbers with relative ease while retaining an OEM-like feel. 550whp is plenty for most and this is a very realistic and obtainable goal.
Moving to 550-650whp it really just comes down to personal preference (& the above factors). Skip the TD-03’s and opt for TD-04 if you go with twins, though. Ultimately, there are plenty of twin and single turbo options that can hit 550-650whp with ease.
At 650+whp I recommend ignoring twin turbo upgrades. Again, there are some setups that can reach these goals (as did the 680whp example from above). However, singles are a bit easier on the engine, and at 650+whp it becomes more about the top-end rather than low-end torque and spool.
Our Personal Setups
Jake and I followed the same general guidelines in deciding on our N54 turbo setups. I opted for RB Twos Plus turbos for my 335i since my goal was ~550whp. Jake went with a Precision 6266 single turbo conversion as his goal was 650-700whp. We both believe they’re the perfect setups for each of our goals.
We also both agree that Jake’s single turbo 135i looks and sounds better. As such, if you really value those factors then you may prefer a ST conversion even if you only want 550whp. Anyway, as one last piece of information on our setups let’s quickly talk about cost.
I am ignoring additional costs here like our fuel pumps, port injection setups, etc. Instead, I simply want to look at the numbers for the turbos themselves and any mods absolutely required for one setup but not the other:
My N54 335i
- RB Twos Plus Twins: $2,200
- Inlets + outlets: $400
- Downpipes: $200
This brings the cost of my N54 twin turbo upgrade to $2,800. I did have inlets & outlets prior to the upgraded turbos, but I’m including the costs since ST conversions don’t require these mods. Well, a ST requires a downpipe but it’s included with N54 single turbo kits.
Jake’s Single Turbo 135i
- SpeedTech PT6266 Gen2: $4,250
- Mac solenoid: $50
- PCV setup: $200
The total cost of Jake’s N54 single turbo conversion comes out to $4,500 – or $1,700 more than my twin turbo N54. It’s a good price for a single turbo, but still highlights the fact that twin turbo upgrades are generally less expensive.
N54 Single vs Twin Turbo Summary
N54 turbo upgrades are a big financial commitment, and if you’re spending the money you want it to feel well spent, right? I know from personal experience it can be challenging and time consuming to decide on N54 single vs twin turbo upgrades.
Big single turbo conversions offer better top-end power and higher peak horsepower. The trade-off is a higher boost threshold, more lag, and less low-end torque. N54 ST setups are also more expensive than twin turbos. However, single turbos can make future life easier and cheaper as the top-mount turbos are simple to maintain or replace.
Ultimately, I recommend sticking with twin turbos around or under 550whp. Twins and singles can both be great options for 550-650whp goals. At 650+whp it’s likely best to cross N54 twin turbos off the list and opt for a single turbo conversion.
I hope this article offers a great starting point for N54 owners looking to upgrade their turbochargers. Once you’re set on the N54 single vs twin turbo debate check out our holistic, in-depth guides for single turbo kits and twin turbo upgrades.