The FIA has clamped down in various 'grey areas' of the engine regulations ahead of 2019.
One unnamed engineer told Auto Motor und Sport: "We have received more technical directives for the engine than ever before."
It follows a period of intense speculation about the so-called grey areas of loopholes in the highly complex power unit regulations.
"We have become stricter in all areas where the engine manufacturers could theoretically overstep the mark," confirmed FIA race director Charlie Whiting.
