BMW 3 Series 320si Engine ReplacementCompare Prices & Get Quotes
Get free, no-obligation quotes today from trusted UK BMW 3 Series 320si engine specialists. Compare prices on reconditioned, rebuilt and used engines for this rare homologation special - the hand-built N45B20A four-cylinder that powered the WTCC racer.
Supply & Fit Available
12-Month Warranty
Nationwide Delivery
100+ Suppliers
From £2,500 to £4,500
Used from £1,200 · Reconditioned from £2,200 · Common codes: N45B20A, N45B20S
From £1,200
Tested, bare/short engine
From £2,200
Rod bearings addressed, tested
From quote
Upgraded bearings, full teardown, revised valvetrain
Secure enquiry - no spam, no pressure. Genuine quotes only from vetted UK BMW 3 Series 320si specialists.
3 Simple Steps3 Simple Stepsto Finding the Best BMW 3 Series 320si Replacement Engineto Finding the Best BMW 3 Series 320si Replacement Engine
Most replacements completed within 3-5 days.
Variant HistoryBMW 3 Series 320si - Engine History & Specs at a Glance
The BMW 320si was a homologation special produced to meet FIA World Touring Car Championship (WTCC) and Super 2000 regulations. Just 2,600 examples were built worldwide between late 2005 and mid-2006, of which only 500 were right-hand drive for the UK market. Based on the E90 320i M Sport, the 320si received a completely re-engineered four-cylinder engine - the N45B20A - which was hand-built alongside BMW's racing engines at the Hams Hall plant.
Variant HistoryBMW 3 Series 320si - Engine History & Specs at a Glance
The BMW 320si was a homologation special produced to meet FIA World Touring Car Championship (WTCC) and Super 2000 regulations. Just 2,600 examples were built worldwide between late 2005 and mid-2006, of which only 500 were right-hand drive for the UK market. Based on the E90 320i M Sport, the 320si received a completely re-engineered four-cylinder engine - the N45B20A - which was hand-built alongside BMW's racing engines at the Hams Hall plant.
BMW 3 Series 320si
Fuel TypePetrol
Engine Size2.0L (1,997cc)
Power Output173hp (127kW) at 7,000rpmEngine History Timeline
September 2005 - August 2006 - N45B20A 2.0-litre 16-valve DOHC, 173hp, hand-built homologation engine
Key Specs Snapshot
Fuel TypePetrolEngine Size2.0L (1,997cc)Power Output173hp (127kW) at 7,000rpmYears Produced2005-2006 (UK)Every engine fitted to the BMW 3 Series 320si is covered below, with UK rebuilt pricing and known failure points.
BMW 3 Series 320si Engine Codes - Specifications & Replacement CostBMW 3 Series 320si Engine Codes - Specifications & Replacement Cost
2.0-litre Petrol (2005-2006, E90 320si)
Power Output173hp (127kW) at 7,000rpmYears Fitted2005-2006Unique FeaturesHand-built engine; carbon fibre cam cover saving 10kg; bore 85mm x stroke 88mm; compression ratio 11.0:1; no Valvetronic system; aluminium alloy cylinder liners; unique cylinder head cast alongside BMW F1 engines
Compatible Trim Levels
- 320si (standard)
- 320si M Sport
Find your exact engine code, specs and UK replacement cost guide.
Used
Tested, ready-to-fit engine
£1,200-£2,500
Reconditioned
Addressed known issues, tested
£2,200-£3,500
Rebuilt
Full teardown, upgraded internals
£2,500-£4,500
Common Failure
The N45B20A is a rare and specialist engine. Parts availability is limited, and BMW main dealers have reported 10-month waits for new engines. The engine is entirely different from the standard E90 320i's N46/N43 units - it cannot be simply replaced with a standard 320i engine. Common issues reported include cold-start stalling, misfiring at low RPM, and idle instability - often related to DME software or fuelling.
The BMW 320si is powered by the unique N45B20A engine - a hand-built, high-revving four-cylinder developed specifically for this homologation special. With only 500 right-hand drive examples ever produced, replacement engines are rare and specialist knowledge is essential. Rebuilt engines through EnginesMarket are rare but available through specialist networks, backed by a minimum 12-month unlimited-mileage warranty.
Why the BMW 3 Series 320si is a Specialist Proposition
Affected Vehicles
BMW 3 Series 320si (N45B20A, 2005-2006)
Typical Failure Mileage
Highly variable - many fail due to age-related issues or low-mileage use
Root Cause
The N45B20A is a completely unique engine, not an evolution of the standard 320i's N46B20. It features different bore and stroke dimensions (85mm x 88mm), wilder camshafts, bigger valves, a higher 11.0:1 compression ratio, and crucially - no Valvetronic system. The engine was hand-built and shares components with racing units. Parts are extremely difficult to source; BMW main dealers have quoted 10-month waits for new engines.
Why It Happens
The N45B20A is a completely unique engine, not an evolution of the standard 320i's N46B20. It features different bore and stroke dimensions (85mm x 88mm), wilder camshafts, bigger valves, a higher 11.0:1 compression ratio, and crucially - no Valvetronic system. The engine was hand-built and shares components with racing units. Parts are extremely difficult to source; BMW main dealers have quoted 10-month waits for new engines.
Dealer (parts + labour)
£300-£600
Specialist (parts + labour)
£200-£400
What it involves
DME software check, fault code reading, idle calibration
Suitability
First step for cold-start or idle issues
1 - 2 daysDealer (parts + labour)
£5,000-£8,000+
Specialist (parts + labour)
£3,500-£5,500
What it involves
Full strip, inspection, replacement of worn components, specialist machining
Suitability
Only viable if engine has not suffered catastrophic failure
1 - 2 daysDealer (parts + labour)
£6,000-£10,000+
Specialist (parts + labour)
£2,500-£4,500
What it involves
Supply & fit, 12-month warranty
Suitability
Often the only option if the engine is beyond repair
1 - 2 days
All prices are indicative UK market ranges based on current UK specialist supplier data.| Repair Tier | Dealer (Parts + Labour) | Specialist (Parts + Labour) | What It Involves | Suitability | Estimated Time |
|---|---|---|---|---|---|
 Engine diagnostics & software update Minor | £300-£600 | £200-£400 | DME software check, fault code reading, idle calibration | First step for cold-start or idle issues | 1 - 2 days |
 Engine rebuild - specialist Best Value | £5,000-£8,000+ | £3,500-£5,500 | Full strip, inspection, replacement of worn components, specialist machining | Only viable if engine has not suffered catastrophic failure | 1 - 2 days |
Full engine replacement - rebuilt/reconditioned Best Value | £6,000-£10,000+ | £2,500-£4,500 | Supply & fit, 12-month warranty | Often the only option if the engine is beyond repair | 1 - 2 days |
Vehicle Value Check
Vehicle Value Check
A typical BMW 3 Series 320si is worth approximately £4,000-£12,000 depending on condition and mileage. Well-preserved examples can command significantly more due to the car's rarity and homologation special status. - Vehicle worth under ~£5,000: a used engine or specialist rebuild may still be viable due to the car's future classic potential. - Vehicle worth ~£5,000-£8,000: evaluate both; reconditioned is viable if keeping the car as a long-term investment. - Vehicle worth ~£8,000-£12,000+: replacement cost is typically justified by the car's rarity and collector appeal.
Our Recommendation
Our Recommendation
If your 320si has developed running issues, start with specialist diagnostics - many idle and cold-start problems are software-related rather than mechanical. If the engine has suffered catastrophic failure, a used or rebuilt N45B20A is the only correct option - a standard 320i engine is not compatible and will destroy the car's value. Given the rarity of the 320si, investing in the correct engine is almost always the right decision for a genuine example.
Don't Let Engine Failure Write Off Your BMW 3 Series 320si
The BMW 320si is one of the most interesting homologation specials of the 2000s - a genuine four-cylinder M3-inspired machine with a hand-built racing engine. With only 500 UK examples ever produced, keeping your 320si on the road with the correct engine is essential. Compare quotes from specialists who understand the N45B20A and get your 320si back on the road with nationwide supply & fit options.
Compare rebuilt N45B20A BMW 3 Series 320si engine prices
12-Month Minimum
UK Specialists Vetted
Best Price GuidanceImportant Information
Important Information
"All prices are indicative UK market ranges based on historical quote data and repair requests from our network of engine specialists. Dealer pricing is estimated based on published main dealer labour rates and genuine OEM parts pricing. Specialist pricing reflects actual quote data from EnginesMarket's UK network. Actual costs vary depending on damage severity, vehicle condition, variant, and workshop location within the UK. Use our free comparison tool to get tailored quotes for your specific BMW 3 Series 320si. Every engine supplied through EnginesMarket carries a minimum 12-month unlimited mileage warranty - always confirm exact terms with your chosen supplier."
BMW 3 Series 320si Engine ReplacementFrequently Asked Questions
Question 1How much does a BMW 3 Series 320si engine replacement cost-
A BMW 3 Series 320si engine replacement typically costs £2,500-£4,500 for a rebuilt unit supply-only, or £3,500-£6,000 fitted by a specialist. Used engines start from around £1,200-£2,500, while reconditioned units range from £2,200 to £3,500.
- Prices are significantly higher than standard 320i engines due to the N45's rarity
- Rebuilt engines carry a 12-month unlimited-mileage warranty
- Supply & fit adds £500-£1,000 in labour due to specialist requirements
Question 2What's the difference between the 320si engine and a standard 320i engine-
The 320si uses a completely unique N45B20A engine, not an evolution of the standard 320i's N46 or N43. Differences include: increased bore (85mm vs 84mm) and shortened stroke (88mm vs 90mm); higher 11.0:1 compression ratio; larger valves and wilder camshafts; no Valvetronic system; aluminium alloy cylinder liners; hand-built construction; and a carbon fibre cam cover saving 10kg.
-> Enter your registration to confirm which engine is fitted to your carQuestion 3Can I fit a standard 320i engine in my 320si-
No - a standard 320i engine (N46 or N43) is not a direct replacement for the 320si's N45B20A. The engines have different bore and stroke dimensions, different cylinder heads, different engine management, and different ancillaries. Fitting a non-original engine will also significantly reduce the car's collector value.
- The N45B20A is a completely unique engine, not a modified N46
- Only an N45B20A is correct for a genuine 320si
Question 4Why are 320si engines so expensive and hard to find-
Only 2,600 320si examples were built worldwide, with just 500 right-hand drive cars for the UK. The engines were hand-built at BMW's Hams Hall plant alongside racing engines. BMW main dealers have quoted 10-month waits for new engines. Parts supply is extremely limited, and many components are unique to this engine.
- Low production numbers mean limited used engine availability
- Hand-built construction means higher manufacturing costs
- The engine shares components with racing units, not standard road cars
Question 5How long does a BMW 3 Series 320si engine replacement take-
A typical BMW 3 Series 320si engine replacement takes 2-4 days for a specialist workshop, assuming the replacement engine is available. However, sourcing the correct N45B20A engine can take significantly longer due to rarity.
- Allow 2-4 days for supply & fit through a specialist
- Sourcing the correct engine may take weeks or months
- Additional time may be needed if unique parts are required
Question 6What warranty comes with a BMW 320si replacement engine-
Every rebuilt and reconditioned BMW 3 Series 320si engine supplied through EnginesMarket carries a minimum 12-month unlimited-mileage warranty. Used engines typically come with a shorter warranty (30-90 days) depending on the supplier - always confirm exact terms before purchasing.
- Rebuilt: 12 months / unlimited mileage minimum
- Reconditioned: typically 6-12 months
- Used: 30-90 days, supplier-dependent
Why Choose UsCompare BMW 3 Series 320siEngine PricesToday
Specialist BMW 3 Series 320si engine suppliers in our network
12-Month Warranty on every rebuilt BMW 3 Series 320si engine
Nationwide UK delivery
supply & fit available
The BMW 3 Series 320si is a rare homologation special - and finding the right engine for it requires specialist knowledge. Our network of vetted UK specialists understands the unique N45B20A engine and can supply the correct replacement for your car. Enter your registration, get free, no-obligation quotes, and keep your 320si on the road with the engine it deserves.
Enter your registration
and get matched with verified BMW 3 Series 320si specialists.