## 1 Introduction  
In search of greener transport solutions, hybrid powertrains based on advanced spark-ignition (SI) engines, usually fueled with gasoline, have become one of the most common propulsion systems in new passenger cars. This solution is successful due to the reduction of SI engine operation at low load conditions [1, 2], and to the lower complexity of the three-way catalyst compared to diesel aftertreatment devices [3]. Regarding the state of the art in SI engines, an extended strategy to enhance fuel economy in this kind of engines is the combination of downsizing and direct fuel injection, while turbocharging is used to compensate the consequent power loss. [PERSON] et al. [4] and [PERSON] et al. [5] demonstrated that downsizing with direct injection allows decreasing the pumping losses and increasing the compression ratio, thus reducing fuel consumption by around 25%. Besides, other interesting strategies are being applied to gasoline engines to improve fuel economy, such as exhaust gas recirculation (EGR), variable valve timing [6], deactivation of cylinders [7], and water injection in the intake ports [8]. Focusing on turbocharging, it is key to apply downsizing in SI engines, so to optimize fuel efficiency, as mentioned above. However, the use of turbochargers in SI engines is also subject to different issues: higher pumping losses and knocking tendency, gas temperature limit at the turbine inlet, slower engine transient response due to turbocharger lag, and compressor surge limit. [PERSON] et al. [9] and [PERSON] et al. [10] demonstrated that introducing cooled EGR leads to a lower knock tendency and allows removing fuel enrichment to control the turbine inlet temperature. Moreover, some improvements have been studied to compensate the turbocharger lag, such as the application of low-viscosity oils [11], advanced bearing technologies [12], mechanically driven superchargers [13], electric boosters [14], and VGT control strategy optimization [15; 16]. Regarding the compressor surge, it is an air stalling phenomenon that results in flow reversal and recirculation within the compressor, which can cause from local instabilities and noise to large flow oscillations and severe damage to bearings, seals, and impellers [17; 18]. Surge appearance is dependent on the compressor design and the upstream and downstream duct geometry [19; 20]. [PERSON] et al. [21; 22] reported that using a tapered duct at the compressor inlet improves the surge margin, while reducing the downstream volume may change the surge dynamics from a low-frequency deep to a high-frequency mild surge [23; 24]. In addition, [PERSON] et al. [25; 26] found by experiments that the surge margin can also be increased under pulsating flow conditions at the compressor outlet, and when using compressor inlet vanes to generate a swirling flow. Despite all these improvements to reduce surge area, this undesirable phenomenon can usually appear in turbocharged SI engines during gear shifts and fast throttle closings, when the engine air flow is abruptly reduced. Under such circumstances, the most widespread solution for surge avoidance is the installation of a recirculation loop in which an anti-surge valve (ASV) is opened when the compressor is getting close to the surge limit, thus connecting its inlet and outlet [27]. Besides, the ASV can be employed to mitigate boost spikes during load increase maneuvers at iso-engine speed, better known as tip-ins [28]. Nevertheless, it must be remarked that the use of this anti-surge control system is also associated with higher turbocharger production costs and additional calibration tasks to properly manage the ASV. In this research, the potential removal of the compressor ASV was assessed in the interest of cost reduction. Hence, the paper is focused on the evaluation of two strategies to manage throttle tip-outs with no anti-surge control system in a turbocharged SI engine equipped with a low-pressure EGR loop.