Evolution of Honda's F1 Power Unit from 2015 to 2021
HONDA RA621H 2021 ｜ A hydraulically operated Intake Guide Vane (IGV) is attached at the inlet of the large-diameter compressor. The IGV has been in use since 2018 when Honda switched its partnership to Toro Rosso (now AlphaTauri). Up until the 2016 RA616H, a throttle was placed at the inlet of the plenum chamber, but starting with the 2017 RA617H, the throttle was eliminated. Torque control is primarily achieved through fuel injection quantity, meaning it is throttle-less. The IGV not only adjusts the amount of air but also controls the angle of airflow entering the compressor to prevent flow separation. The engine oil tank is visible to the left of the IGV.
Since rejoining F1 in 2015, Honda has adopted a layout where the compressor is positioned at the front of the engine, the turbine at the rear, and the MGU-H located behind the compressor. The Inconel turbine housing, featuring a twin volute design, has been manufactured using 3D printing (additive manufacturing) since 2020, produced in-house by Honda. The whitish appearance of the surface is due to thermal insulation coating. Choice between one or two wastegate(s) to use is decided by disucssions of Honda and the team. To enhance exhaust sound, fitting one or two dedicated wastegate pipes has been mandatory since 2016.
Comparing with the photo of P005, it is clear that the exhaust pipes are not symmetrical. The MGU-K, which is regulated to a maximum output of 120 kW, is located beside the lower block on the left side. On the right side, auxiliary components such as the scavenging pump and water pump are concentrated. The HONDA logo is affixed to the plenum chamber. Air cooled by the charge air cooler (intercooler) enters the chamber from the front (right side of the photo). Inside, there is a Variable Intake System (VIS), which operates similarly to the IGV using a hydraulic actuator, allowing for adjustable intake pipe lengths (details from P040 onwards).
The gold-colored pipe visible at the front of the cylinder head cover directs compressed air from the compressor to the CAC. The CAC stands for Charge Air Cooler, commonly known as an intercooler. There is a similar pipe on the opposite side. One of the highlights of the RA621H is the addition of a bypass pipe to these pipes. This is part of an energy recovery technology called CB2, which utilizes excess boost pressure that was previously vented upstream of the intake system by redirecting it to the exhaust to drive the turbine (details on P062). The absence of reinforcement ribs on the exhaust side of the cylinder head cover is intended to contribute to the design of the vehicle's body (cowl).
