Do you have a BMW with an N54 twin-turbo engine? Then, possibly, you may get in a dilemma to pick between its 6 bolt and 8 bolt flywheels. The number of bolts refers to how the flywheel is attached to the crankshaft. But that’s not enough! There are more things to talk about N54 6 bolt vs. 8 bolt flywheels.
The 6-bolt and 8-bolt flywheels are associated with the N54 engine. They are similar in function but with differences that affect their performance, durability, and cost. Typically, the 6-bolt flywheel is found in Romeo engines. Alternatively, the 8-bolt flywheel is common in Windsor engines (1).
In today’s blog, I will illustrate an in-depth comparison of these two types of flywheels. After reading this, you can understand their functionality correctly. Also, you can easily decide on them for your N54 engine.
Comparison of N54 6-Bolt and 8-Bolt Flywheels
The 430lbs, 3.0L BMW N54 engine features an aluminum open-deck block, aluminum head, and a forged crank and rods for strength (2, 3). It can produce between 300-335 horsepower and 300-332 lb-ft of torque, depending on the model (4). However, the most potent iteration of the N54 was introduced in 2011, delivering 335 hp at 5,900 rpm (5).
In such powerful engines, flywheels are essential components. They are typically found at the rear of the machine. They work as energy storage devices. Hence, these flywheels smooth the power delivery from the crankshaft to the transmission. You can get a stable drivetrain for these components as power transfer happens flawlessly.
However, the dilemma of 6-bolt and 8-bolt flywheels appears in the air as the N54 engine has these two distinct bolt patterns (holes). Let’s talk about the differences between these flywheels.
Definition of 6-bolt and 8-bolt Flywheels
Well, the number of bolts refers to the crank flange bolt pattern. It must match between the engine and the flywheel (6). According to a forum discussion, if your car originally has a 6-bolt flywheel and needs a new crank, you may need to switch to an 8-bolt crank and flywheel (7).
You can identify the engine type by the number of valve cover bolts. If it has 11 bolts, it indicates a Romeo engine. Similarly, 13 bolts indicate a Windsor engine (8). Despite the differences, both flywheels serve the same function in the engine, storing and releasing kinetic energy.
Durability
The durability and longevity of the flywheel are affected by the number of bolts. For instance, the increased number of bolts in 8-bolt flywheels has a longer lifespan and higher durability than 6-bolt versions (2).
Compatibility
The N54 engine, depending on its production date, can have either a 6-bolt or an 8-bolt flywheel. If your car has an engine produced from 2/2009 onwards, it may have a 6-bolt mounting hub. But the earlier models use an 8-bolt crankshaft (9).
The 8-bolt flywheel is used in early N54 engines in the E82 135i, E9X 335i/xi, and E60 535i/xi (10). On the other hand, the 6-bolt flywheel is used in late N54 engines (11). Typically, this flywheel is compatible with the 1997 or earlier 4.0-liter engine. They switched to an 8-bolt flywheel in 1998 (12).
Strength
As I said, the 6-bolt flywheel is compatible with N54 and N55 engines, though earlier models use an 8-bolt crankshaft. However, I found no explicit discussion over the strength comparison between the 6-bolt and 8-bolt flywheels. Possibly, the durability of 8-bolt flywheels ensures that they have better strength.
Clutch Compatibility
You can find several clutch kits compatible with the N54 6-bolt flywheel. The 335is/550i 6-speed Clutch Kit from ECSTuning is a popular choice. It includes a clutch friction disc, throwout/release bearing, clutch fork lever, pressure plate, and pressure plate bolts (13). Some other recommendations are the Mfactory Racing Clutch Kit, and DKM Stage 3 Performance Twin Disc Clutch Kit (14, 15).
Similarly, the 8-bolt flywheel is compatible with specific clutch kits like Centerforce ll Organic Clutch Kit (16). Eaton’s clutch installation guide indicates that installing an 8-bolt flywheel requires specific bolt sizes. It recommends 8 bolts M10x1.5 for 380 mm and 395 mm flywheels (17).
Cost
The price difference between 6-bolt and 8-bolt flywheels depends mainly on the brand and discounts (if available). Usually, a 6-bolt flywheel for N54 and N55 engines starts at around $441.74. Some options are available with discounts (18). On the other hand, an 8-bolt flywheel from Turner Motorsport is available for $420.69 after a 30% discount (19).
The original price of an OEM replacement flywheel for early N54 cars with 8 mounting bolts is significantly higher, like I saw to date, $603.71 (20). I got another interesting thing – Mfactory flywheels are available in both 6 and 8-bolt versions. These are comparatively better choices for saving money (21).
Applications
For sure, the 6-bolt flywheel is more suitable for everyday driving and light performance applications. There are reasons behind this. Its lighter weight and lower cost are better if you prioritize responsiveness and cost-effectiveness over high-torque performance.
Alternatively, you can select the 8-bolt option for high-torque applications and performance driving. These flywheels can provide better power and performance.
Advantages and Disadvantages
As I said, flywheels with fewer bolts are likely to be lightweight. These things allow the engine to rev more freely. Also, they can improve vehicle performance. But they may also cause changes in RPM to occur more slowly (22). They can even handle less torque than the 8 bolt flywheels.
On the other hand, dual-mass flywheels like 8-bolt offer smoother clutch operation. These are also good for gear-shifting improvements and reduced vehicle vibration (23).
Can I use an 8-bolt instead of a 6-bolt in My Car?
Yes, it is technically possible to use an 8-bolt flywheel instead of a 6-bolt one. But this may typically require some modifications to your vehicle. Indeed, the 8-bolt and 6-bolt flywheels are designed to fit different versions of the N54 engine.
These flywheels are not directly interchangeable. Since the earlier versions of N54 engines had 8-bolt options, it will surely require modifications to later 6-bolt flywheel engines. In the same way, you need modifications or replacements if you want to use 6-bolt instead of 8-bolt.
However, I suggest you consult with a professional mechanic or a BMW specialist before making any modifications.
Which One Should I Choose: N54 6-Bolt vs. 8-Bolt Flywheel?
Both flywheels offer undoubtedly good benefits. But which one will you pick for your vehicle (except that modification-thing)? Well, you should not forget that 6-bolt and 8-bolt flywheels are made for different models of N54 engines. So, there should be some factors which you should consider when choosing between them.
Vehicle Type and Usage
For everyday driving, the 6-bolt flywheel is the most suitable choice. Alternatively, the 8-bolt flywheel is a better option for high-torque applications and performance driving.
Budget Considerations
Financial considerations are also important. Remember, the 6-bolt flywheel is generally less expensive than the 8-bolt version. On the other hand, the 8-bolt flywheel may offer longer-term cost savings due to its increased durability and lifespan.
Maintenance and Replacement
Both flywheels have their specific maintenance needs and replacement intervals. These things can impact long-term costs and vehicle downtime.
Final Words: N54 6 Bolt vs. 8 Bolt Flywheel
How was the discussion – easy to understand or interesting to read? I guess I have used simple explanations with interesting facts throughout the blog. Choosing a flywheel with the right bolt numbers is essential to get the desired driving experience.
If you are a regular driver or take your vehicle very frequently, a 6-bolt is suitable for your N54 engine. But you can select the 8-bolt option if you need high performance and power.
That’s all for today. Thank you for sharing your moments.
