BMW 320d vs 330d: 4-Cyl or 6-Cyl Diesel 3 Series?
320d or 330d is the most-asked engine question by every UK 3 Series diesel buyer. The 320d (B47 4-cyl) is the workhorse: 184-190 bhp, 50+ mpg, the modal UK used 3 Series. The 330d (B57 6-cyl in LCI F30 / G20; N57 6-cyl pre-LCI) is the long-distance luxury pick: 258-265 bhp, smoother delivery, 6-cylinder torque and refinement at 5-7 mpg lower economy. This guide covers the 4-cyl-vs-6-cyl trade-off.
Quick verdict
320d for almost every UK buyer. 330d for long-distance drivers who value 6-cylinder refinement and don't mind 5-7 mpg lower economy. Used pricing: 330d commands £2,000-£5,000 premium over 320d for equivalent year and mileage. The 6-cyl smoothness is genuine but the 4-cyl B47 in M Sport spec is objectively a good car. Pre-LCI 330d (N57 6-cyl) carries the famous swirl flap concern (£250-£450 preventative); 320d doesn't have it. Post-LCI 330d (B57) resolves swirl flaps.
Side-by-side comparison
| Dimension | 320d | 330d | Notes |
|---|---|---|---|
| Cylinders | 4 (I4) | 6 (I6) | The defining mechanical difference. |
| Power (post-LCI) | 190 bhp (B47) | 258-265 bhp (B57) | 330d has 35-40% more power. |
| Torque | 400 Nm (B47) | 560-620 Nm (B57) | 330d significantly torquier. |
| 0 to 60 mph | 7.1-7.5 seconds | 5.4-5.7 seconds | 330d is meaningfully quicker. |
| Real-world UK MPG | 50 to 58 mpg combined | 42 to 50 mpg combined | 320d wins by 5-7 mpg. |
| ULEZ compliance | Build-date dependent (post-LCI B47 yes) | Build-date dependent (post-LCI B57 yes) | Same logic on both. |
| Swirl flap concern | No (B47 doesn't have them) | Yes on pre-LCI N57; no on post-LCI B57 | Pre-LCI 330d carries the N57 swirl flap risk. |
| Used buyer pool depth | Largest UK 3 Series pool | Smaller pool; commands premium | 320d is everywhere; 330d is the 'one-step-up' pick. |
| Towing capacity (braked, kg) | 1,800 kg typical | 2,000 kg typical | 330d wins for heavier towing. |
| Insurance group (UK) | Group 22-28 | Group 28-34 | 330d ~£150-£300/year more. |
| Used price premium | Baseline | + £2,000 to £5,000 | Premium varies by year and condition. |
320d: deeper look
The 320d (B47 LCI, N47 pre-LCI) is the UK 3 Series of the F30 and G20 era. 50 to 58 mpg combined, 60-68 mpg on a long motorway run, 184-190 bhp adequate for everyday use. The B47 is mechanically simple (single-turbo I4) with well-understood wear pattern: EGR cooler recall verification, NOx sensors past 60k. No swirl flaps. 320d M Sport in F30 LCI (2015+) is the modal UK used buy at £12,000-£17,000 in 2026. G20 320d M Sport is the freshest spec at £20,000-£32,000 depending on year.
330d: deeper look
The 330d (B57 LCI, N57 pre-LCI) is the long-distance refinement pick. 258-265 bhp, 5.4 to 5.7-second 0-60, 42 to 50 mpg combined, 55-62 mpg on long runs. The 6-cylinder character is genuinely different from the 4-cylinder: smoother idle, more linear power delivery, less perceived effort at motorway speeds. Pre-LCI N57 330d carries the swirl flap preventative concern (£250-£450 to blank or replace at 80k+ miles); post-LCI B57 330d resolves swirl flaps. Used pricing: F30 330d M Sport at £15,000-£23,000; G20 330d M Sport at £25,000-£40,000.
Decision logic
Three filters decide 320d vs 330d. First: do you do more than 15,000 motorway miles per year? 330d's smoothness becomes genuinely valuable on long runs. Second: do you tow regularly (over 1,500 kg)? 330d's torque and 2,000 kg rating wins. Third: is the £2,000-£5,000 premium worth the 1.7-second 0-60 advantage and the 6-cyl character? For most UK buyers, 320d is enough. For long-distance / towing / character-conscious buyers, 330d is the right call. The 320d is not a 'lesser' choice; it's the modal 3 Series for a reason.
UK 2026 pricing comparison
| Scenario | 320d | 330d | Notes |
|---|---|---|---|
| 2014 F30 320d M Sport (pre-LCI N47), 90,000 miles | £7,500 to £10,000 | £9,500 to £13,000 (330d N57 equivalent) | Pre-LCI; chain risk on N47; swirl flap risk on N57. |
| 2017 F30 320d M Sport LCI (B47), 70,000 miles | £12,000 to £15,000 | £15,000 to £19,000 (330d B57 LCI equivalent) | Post-LCI; ULEZ; 330d commands ~£3,000 premium. |
| 2019 G20 320d M Sport, 50,000 miles | £18,000 to £22,000 | £22,000 to £27,000 (G20 330d equivalent) | G20 era; clean used buys. |
| 2022 G20 320d M Sport MHEV LCI, 30,000 miles | £28,000 to £33,000 | £33,000 to £40,000 (G20 330d MHEV LCI equivalent) | Post-LCI G20; freshest used spec. |
| 2017 F31 320d M Sport LCI Touring, 70,000 miles | £13,000 to £16,500 | £16,500 to £20,500 (F31 330d Touring equivalent) | Touring premium plus 330d premium stack. |
Recommendation by scenario
| Scenario | Pick | Why |
|---|---|---|
| City commuter / under 10,000 miles/year | 320d | 330d's extra power and refinement are wasted on city driving. 320d is around £600-£900/year cheaper to run on fuel alone. |
| Long-distance commuter (15,000+ miles/year) | 330d (post-LCI B57) | I6 smoothness genuinely valuable on long runs. The MPG penalty narrows on motorway. Worth the £2,000-£5,000 used premium for the daily quality of life. |
| Family + occasional towing | 330d | 2,000 kg tow rating and 6-cyl torque pull caravans / horse-boxes more comfortably than 320d's 1,800 kg / 4-cyl. |
| Enthusiast / wants the better-engineered diesel | 330d (post-LCI B57) | B57 6-cyl is one of BMW's strongest modern engines (300,000+ mile cars documented). Post-LCI resolves swirl flaps. The 'one-step-up' refinement pays back over years of ownership. |
| Tight budget (sub-£12,000) | 320d (post-LCI B47) | 330d at this price point is mostly pre-LCI N57 (Euro 5, swirl flap risk). 320d LCI B47 at sub-£12,000 is the better value buy. |
| Buying as future classic / appreciation | 330d (any 6-cyl variant) | BMW will eventually stop selling diesels. 6-cylinder turbodiesel will become the 'modern classic' diesel pick. 330d holds value better than 320d over long horizons. |
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Frequently asked questions
Is the 330d worth the premium over 320d?
Depends on annual mileage and motorway proportion. Over 15,000 miles per year of mostly motorway driving, the 330d's smoothness pays back in driver quality of life over years. Under 10,000 miles per year of mostly city driving, the 320d wins on running cost and the 6-cyl refinement is rarely felt. The £2,000-£5,000 premium is real money that's better spent on better-spec'd 320d for most buyers.
What's the difference between N57 330d and B57 330d?
N57 is the pre-LCI 6-cyl diesel (2012-2015 in F30); B57 is the post-LCI version (2015 onwards). B57 added Euro 6 emissions, resolved the swirl flap concern (no longer fitted), and improved fuel economy by 2-3 mpg. B57 is meaningfully better; if buying 330d, target B57 spec or accept the swirl flap preventative on N57.
Should I buy a pre-LCI 330d?
Only with documented swirl flap preventative work AND ULEZ exemption status. Pre-LCI N57 330d (2012-2015) is Euro 5 (NOT ULEZ-compliant) and has the swirl flap concern (£250-£450 to blank or replace). The cheapest pre-LCI 330d cars are tempting but stack two long-tail expenses. Post-LCI B57 330d resolves both.
Is the 320d underpowered?
No. 184-190 bhp is genuinely enough for daily use including motorway overtakes. The B47 has 400 Nm of torque from low revs (similar to many petrol V8s 15 years ago). The 320d M Sport with the 8-speed ZF auto is a quick, modern diesel; comparison to 330d's 258-265 bhp makes it feel modest, but in isolation the 320d is more than adequate.
320d or 330d for towing a caravan?
330d. 2,000 kg braked tow rating vs 320d's 1,800 kg. The 6-cyl torque (560-620 Nm vs 400 Nm) makes hill starts and motorway pulls with a caravan meaningfully less stressed. For caravans over 1,500 kg, 330d is the practical choice.
What's the 320d ULEZ status?
Build-date dependent. Pre-LCI 320d (typically pre-mid-2015) is N47 Euro 5 (NOT ULEZ-compliant). Post-LCI 320d (mid-2015 onwards) is B47 Euro 6 (ULEZ-compliant). G20 320d (2019+) is ULEZ-compliant from launch. Always verify on V5 emissions class.
Is the 6-cyl really that much smoother than the 4-cyl?
Yes at idle and at low revs. At motorway cruise (1,800-2,200 rpm) the difference narrows; both are quiet and smooth. The 6-cyl advantage is most pronounced from cold start, in stop-go traffic, and on the first 30 seconds of any drive. It's a quality-of-life upgrade rather than a fundamental driving difference. Test-drive both back-to-back if you can.
330d or 335d?
335d is the older bi-turbo version of N57 with 313 bhp (pre-LCI F30 only; F30 LCI moved to the 340d badge that wasn't UK-sold). The 6-cyl bi-turbo carried more complexity and higher cost. For the buyer who wants more performance, modern 330d (B57) with the 8-speed ZF auto is roughly equal to 335d in real-world performance with cleaner emissions. 335d is rare UK volume; 330d is the practical pick.
Does the 330d have the same engine as the 330d Touring?
Yes. Same engine, same gearbox, same chassis layout. Only the body differs. F31 (Touring) and F30 (Saloon) share everything mechanically including the 330d powertrain.
Will BMW continue making the 330d?
Production-pending. BMW announced no current diesel will be developed beyond 6-cylinder twin-turbo configurations. The 330d (B57 single-turbo I6) continues for now but the long-term direction is electrification. 330d's investment / classic potential is rising for that reason; clean low-mileage 330d (especially Touring) is a quietly appreciating asset class.