| Subaru CB engine | |
| Manufacturer: | Subaru |
| Configuration: | Flat-4 |
| Production: | 2020 - present |
| Fueltype: | Petrol/gasoline |
| Compression: | 10.4:1 |
| Valvetrain: | DOHC 4 valves x cyl. with AVCS |
| Turbocharger: | Yes |
| Coolingsystem: | Water-cooled |
| Fuelsystem: | Fuel injection |
| Predecessor: | FB, FA (split diagonally) |
The Subaru CB engine is a gasoline boxer-4 engine used in Subaru automobiles. It is the fourth generation of Subaru boxer engines, following the first (EA, 1966–94), second (EJ, 1989–2021), and third (FB/FA, 2010/2012–present) generations.
The CB engine was first introduced in August 2020 with the second-generation Levorg.[1] [2] According to Subaru, CB stands for Concentration/Compact Boxer.[3] It is the fourth-generation boxer engine family from Subaru.[4] Compared to the preceding FB series, the CB is shorter; the bore pitch (centerline to centerline spacing between adjacent cylinders) has decreased from 113mm98.6mm and the overall crank length has decreased from 350.5mm315.9mm.[5]
For the first time in a Subaru engine, the centerlines of the cylinder bores do not intersect with the crankshaft axis; instead, there is a crank offset of 8mm. This offset reduces friction during the piston downstroke. Overall thermal efficiency is 40% due to the adoption of lean-burn combustion with an excess air ratio (λ) of 2.[5] The injector is positioned next to the spark plug in the center of the combustion chamber to ensure the lean mixture will ignite reliably. A small single-scroll turbocharger was equipped to maintain charge air volume and improve throttle response.[5]
The connecting rods in the CB engine are split horizontally,[3] like those in the second generation EJ engines.[5] [6] The third generation FB/FA connecting rods are split diagonally[7] (also called an offset or asymmetrical connecting rod) to allow a longer piston stroke without increasing the width of the engine,[8] but the horizontally-split connecting rods are stronger.[3]
The first engine in the series is designated CB18, a 1.8 litre dual overhead cam 16-valve engine featuring dual AVCS with gasoline direct injection and a turbocharger.[9] Compared to the FB16 used in the previous generation of the Levorg, the CB18 offers decreased fuel consumption (16.6km/L for the CB18 and 16km/L for the FB16, both using the JC08 mode) and increased torque (300Nm for the CB18 and 250Nm for the FB16). In addition, the CB18 achieves its peak torque at a lower engine speed.[5] Engine weight of the CB18 has been reduced by 14.6kg (32.2lb) compared with the FB16.[5]
In October 2020, Subaru announced the CB18 also would be fitted to the top-of-the-line 'Sport' trim of the 5th generation Subaru Forester in the Japanese market; other models of the Forester are equipped with the mild hybrid FB20D e-BOXER.[10]
The CB18 engine is also fitted to the Subaru Legacy Outback for the Japanese market.[11] [12]
In April 2022, Subaru had to suspend production of Forester, Outback and Levorg after it discovered a sensor in CB18 engine malfunctioned.[13]
(ja|[[:ja:スバル・CB型エンジン|Subaru CB engine]])