BMW started offering models such as the M340i and the M550i which have elements of M Performance without compromising drivability and comfort.
The BMW G20 M340i was first introduced in 2019, representing the highest-performing BMW 3-Series model before getting into BMW M3 territory. On the other hand, the BMW G30 M550i came out in 2017, and it also represents the highest-end BMW 5-Series model, only shy of the BMW M5.
How does the BMW G20 M340i compare to the larger G30 M550i in terms of performance, tuning, interior, drivetrain, styling, reliability, and price? Here is a full head-to-head comparison between these amazing BMW sedans.
| BMW G20 M340i | BMW G30 M550i | |
| Engine Code | B58B30O1 | N63B44O2 – N63B44T3 |
| Engine Configuration | Inline-6 | V8 |
| Displacement | 3.0 L (2,993 cc) | 4.4 L (4,395 cc) |
| Turbos | Single twin-scroll turbo | Twin-turbo |
| Horsepower | 382hp at 5,800–6,500 rpm | 456hp – 523hp at 5,500–6,000 rpm |
| Torque | 369lb-ft at 1,800–5,000 rpm | 479lb-ft to 553lb-ft at 1,800–4,750 rpm |
| Transmission | 8-speed ZF 8HP automatic | 8-speed ZF 8HP automatic |
| Dimensions | Length: 4,709 mm (185.4 in), Width: 1,827 mm (71.9 in), Height: 1,442 mm (56.8 in) | Length – 4,936 mm (194.3 in), Width: 1,858 mm (73.1 in), Height: 1,479 mm (58.2 in) |
| Weight | 1758 Kg / 3876 lbs. | 1885 Kg / 4156 lbs. |
| 0-60mph | 4.1 seconds (xDrive) – 4.3 seconds (RWD) | 3.6 seconds |
BMW M340i vs. M550i: Engine & Performance
The BMW G20 M340i comes with a straight-six B58B30O1 engine that replaced the older N55 straight-six with a hefty 20% increase in boost pressure, a new closed-deck engine design, a slight decrease in displacement, a higher compression ratio, but with more power and more torque. (382hp and 369lb-ft of torque)
On the other hand, the M550i uses a comparably larger N63B44O2 (456hp and 479lb-ft)for the pre-LCI M550i or the updated N63B44T3 (523hp and 553lb-ft)for the LCI model (2020 and later). The N63 V8 replaced the outgoing N62 naturally aspirated engine, and it debuted the “hot-vee” layout where the turbochargers are placed within the “V” of the engine.
The M340i uses single-turbo inline-6 and the M550i uses a twin-turbo V8
The base differences between these two engines are that the one in the M550i is larger both in capacity and displacement and it uses two turbochargers while the one on the M340i uses a single twin-scroll turbocharger. The N63 engine sounds better than the B58. Another benefit of the V8 is the low-end torque.
The M550i is faster stock than the M340i as it can achieve the 0-60mh sprint around half a second quicker than the B58 while also reaching the quarter mile in 11.8 seconds compared to 12.2 seconds for the M340i.
Related: M340i 3 Series vs. 540i 5 Series
BMW M340i vs. M550i: Tuning
The B58 and the N63 are highly tunable engines, but the N63 of the M550i has a much higher power limit. The best mods for the M340i include catless downpipes, aftermarket intake, and a tune. If you want massive power gains, you can round up these with an upgraded fuel pump and a larger turbocharger.
The N63 also fares very well with increased power. Similarly, it can benefit from a catless downpipe, a tune, and upgraded fuel injectors. Just a few mods will give you more horsepower throughout the rev range, it is indeed a tightly tunable engine. Just like the B58 of the M340i, the M550i benefits massively from a turbo upgrade.
The M340i’s B58 and the M550’s N63 are highly-tunable engines
The maximum boost the B58 can handle with stock turbos is around 20PSI while the N63 can handle up to 25PSI. Stock turbos will let you get to quite high power numbers, around ~650 WHP on the M340i and around ~700WHP on the M550i. If you’re unsatisfied with these power numbers, there are turbo upgrade kits for both engines.
BMW M340i vs. M550i: Drivetrain
The drivetrain aspect of these two cars is similar, but not the same. The M340i can be had in pure RWD form which saves some weight and ensures the classic BMW 3-Series rear-wheel drive straight-six fun while the BMW M550i is only available with the BMW xDrive AWD system. However, the M550i’s xDrive system can be switched to RWD only which makes it capable of similar hooliganism as the M340i.
The M340i can be had in RWD or AWD, while the M550i is AWD only
Both are only offered with the great ZF 8-speed automatic torque converter transmission which is considered the golden standard of automatic transmissions. This also includes launch control on both models which gives you the best 0-60mph times you can get.
BMW M340i vs. M550i: Reliability
BMW managed to improve its overall reliability over the past few years as it now holds the 10th spot on the J.D. Power Vehicle Dependability Study which includes 32 different brands. WhatCar, a prominent British independent motoring magazine rates the G20 3-Series with an impressive 97.3% reliability rating while the 5-Series got a 96.9% reliability rating which puts these two in a similar group.
The M340i will be more reliable long-term
The reason why the 3-Series managed slightly better results could be because the B58 is more reliable than the N63. The B58 of the M340i has a better track record as far as reliability is concerned. On the other hand, the reliability of a BMW twin-turbo V8 car such as the M550i is much more debatable. The N63TU is a reliable engine, but there is no doubt that the straight-six of the M340i will have fewer issues.
Another reason the M340i is more likely to be reliable is it is equipped with fewer electronics. The M550i interior is feature-packed, which adds complexity and possible points of failure to the vehicle.
BMW M340i vs: M550i: Exterior Looks
BMWs exterior design has become somewhat controversial in the past few years, especially with the new BMW M3/M4, the new BMW iX, the new BMW 2-Series, and the latest BMW i7/7-Series. Thankfully, both the M340i and the M550i still retain BMWs old-school approach to exterior design which makes them the best-looking models from their lineup except for the BMW M5.
Both the M340i and the M550i are some of the best-looking modern BMWs
Given its larger dimensions and stunning looks with the M-Sport package, the M550i has more road presence while the M340i is more subtle. It’ll be hard to drive unnoticed in an M550i as the big wheels, prominent rear, and V8 rear lets everyone know you’re in a big German sports sedan. Most people won’t bat an eye at the M340i as long as you keep the exhaust out of Sport mode.
BMW M340i vs. M550i: Interior
The BMW F30 3 Series was widely criticized for having an interior design that wasn’t significantly improved from the E90 3 Series. BMW stepped up interior design for the G20 bringing a much-needed refresh with improved materials and layout. However, the M550i wins in the interior department as it is more refined, premium, and spacious.
The BMW 5-Series is a class above the 3-Series which means that everything is more upscale on a 5-Series. The choice of materials takes a decent leap while features are also better with the M550i.
BMW M340i vs. M550i: Price & Value
You can expect to pay around $54,000-$57,000 for a brand-new 2022 BMW G20 M340i while the 2023 BMW G30 M550i is going to cost you around $77,000. This is a $20,000 difference between the two. Those who prefer driving dynamics and aren’t too fussed about leaps of luxury are likely to think that the M340i offers better value while those who appreciate luxury will deem the M550i as better value as it is a baby M5.
However, the M340i is going to depreciate less and is also a more fuel-efficient vehicle. This means that the $20,000 difference between the two is just the begging. The M550i will also require more maintenance in the long run.
Our verdict
To conclude, the M340i is the one to go for if you want better value and you care mostly about how a car drives, how reliable it is, and if you prefer the old-school BMW straight-six setup. The B58 is an extraordinary engine and an excellent combination of practicality and reliability with performance.
On the other hand, if you want a larger family car with more space, more luxury, and a powerful V8, the M550i is the better choice. It will cost you more, but it’ll stand out on the road and give you more than enough performance.