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36 The AV-21’s K20C engine is a 2.0 litre four-stroke built largely from aluminium, spark-ignited, turbocharged and featuring four cylinders, each with an 86 mm bore and 85.9 mm stroke. In standard configuration it provides up to 306 bhp continuously (228 kW, although during PoliMove’s record run the engine sustained a 500 bhp peak) at 6500 rpm. It has a 9.8:1 compression ratio, and maximum torque of 400 Nm is achieved at 2500 rpm. “For this season, we put a bigger turbo on the car that will give teams an extra 100 bhp, along with a different fuel pump that raises the capacity of fuel we can send to each cylinder,” says Keats. “That means in total the AV-21 now puts around 473 bhp at the wheels.” The engine forms a stress member and hence a structural part of the car, with the only real dampers being in the suspension, limiting the extent to which engine noise can be filtered out. That had a great bearing on how the IAC’s partners and teams immunised their sensor data inputs. “That’s a key part of how this application pulls out and resolves edge cases that appear only sporadically at best in commercial or consumer vehicles,” Keats says. Although changing the engine from that in the standard IL-15 car meant making considerable adjustments to the K20C to fit it into the structure and resonances of the AV-21, the IAC still chose the new engine, primarily because it made for far easier maintenance and servicing than the old one. That was a critical factor in checking and replacing the cable harnesses for the sensors and controls that are key to safe autonomous driving, in addition to being slightly less expensive and not particularly different in speed and power. Coffey says, “The changes to the K20C included switching to a dry sump, as that made for a flat oil pan fitting under the engine that attaches to the monocoque, with an oil tank and reservoir system off the front of the engine. That switch also ensured a similar overall powertrain weight to that in the Indy Lights car. “Then we built a trunnion to connect the gearbox and bellhousing to the monocoque, above the engine, as well as an aluminium bracket to connect the front of the K20C to the monocoque. It’s similar to installations used in some Formula series.” He adds that the dry sump is 7075 aluminium, the engine bracket is 6061, and the trunnion is 4130 steel. “We initially drew all of them in CAD, although for the trunnions we first installed one on the car and used it as a weld-jig, before building a weld-jig off that and then using it to make parts that matched for all the cars.” The air intake is located on the left side of the car, as is the intercooler, which required some redesign, as the K20C’s throttle sits on the right, and now the intake plumbing runs through the bellhousing. More recently, the engine cover has been redesigned to make room for the bigger turbocharger. Engine control (including throttle and shifting) takes place through the Motec ECU, which Keats comments is a particularly flexible COTS unit used in vehicles from street cars to professional racecars, which teams could therefore October/November 2022 | Uncrewed Systems Technology The engine forms a structural member of the car, and eliminating its noise impact on the sensors was a major focal point for the engineering teams An additional draw of the Honda engine was its ease of maintainability. Between races, it must be easy to check and replace the sensors and cable harnesses (Courtesy of Clemson University)