In 2017, Viscaal made the switch to formula racing and made his debut in Formula 4 in both the SMP and Spanish Formula 4 Championships for MP Motorsport. In the SMP championship, he won four races at the Ahvenisto Race Circuit, the Auto24ring and the TT Circuit Assen (twice), finishing second in the final standings with 218 points behind Christian Lundgaard. In the Spanish championship, he won five races at the Circuito de Navarra, the Circuit de Barcelona-Catalunya, the Circuit Paul Armagnac (twice) and the Autódromo do Estoril, yet again finishing second in this championship behind Lundgaard with a 266 points deficit.