Cheap BMW 8 Series Cylinder Head

The BMW 8 Series (G15/G14/G16) has been in production from 2018 onwards, so there is only one generation to consider here, but engine variants changed across the range and there were running production updates, so fitment depends entirely on matching the engine code rather than the year alone. Get the engine code from your V5 or a VIN check and supply it to the breaker, who can confirm whether a specific donor head crosses any mid-production boundary for your exact build date. Never assume a head fits purely because the model year looks close.

Both years sit within the same G15 generation (2018 onwards), and the 840i uses the B58 straight-six petrol engine throughout that range, so on paper the engine code is the same. However, ancillary and mounting details can change mid-production, so confirm against your specific registration with the breaker before buying. Matching the engine code is the essential starting point.

Yes, trim level here does reflect a genuine mechanical difference: the M850i uses the N63 V8 engine while the 840i uses the B58 straight-six, so their cylinder heads are completely different parts and will not interchange. Trim name in this case tells you the engine family, but always cross-reference the engine code on your V5 or via a VIN check to be certain of your exact variant. Supply the engine code to the breaker rather than the trim name alone.

No, body style does not affect cylinder head fitment — the head follows the engine code, not whether the car is a two-door coupe, convertible (G14) or four-door Gran Coupe (G16). As long as the engine code matches, a head from any body style variant will be mechanically equivalent. Focus on confirming the engine code with your breaker and ignore the body style on the donor car.

This is something you should confirm with the breaker and your fitting garage rather than assume either way, as BMW engines can involve coding considerations that vary by variant and build date. A reputable breaker will be able to advise on what they know about the specific unit they are supplying. Make sure your fitting garage is aware the part is from a used donor vehicle so they can check for any required coding steps.

The 840d uses the B57 straight-six diesel engine, and heads must match the engine code exactly, so you cannot fit a B57 head to any petrol variant regardless of year or trim. Within the 840d diesel line, the engine code is the critical identifier, but confirm with the breaker against your registration whether any mid-production changes to the B57 affect the specific unit you are looking at. Fuel type is an absolute fitment boundary — diesel and petrol heads are never interchangeable.