Honda will use the same concept design that they introduced in 2017, only the 2019 version will be of further evolution. The team feels there is still more potential to the engine.
The Japanese manufacturer re-joined Formula 1 in 2015, supplying engines for McLaren, but endured a tough spell with reliability issues, causing the partnership to split at the end of 2017, enabling Toro Rosso to acquire the engines.
Honda F1 technical director Toyoharu Tanabe said that "We don't know exactly [what the limit is] because we haven't achieved a high level but we started with another concept and changed it for 2017,” (autosport.com).
"We learned something earlier, then changed it. In 2018, we carried over this concept and improved reliability and performance.”
"We can carry over the current design, or concept, of power unit.”
After a relatively impressive season with Toro Rosso last year it convinced the parent Red Bull team to switch engines from Renault to Honda for 2019.
Honda feels that because the two teams are so closely linked it can give the engine suppliers a boost.
"Toro Rosso and Red Bull has communication and that's easier for the Red Bull side because Toro Rosso knows our power unit. They can communicate a problem or a kind of concern from the chassis point of view, and they can come back to us.”