Dominant team Red Bull stands to lose a chunk of laptime if diffuser exhaust blowing is banned after Sunday's Canadian grand prix.
The team's engine supplier Renault argued for a delay of the ban until after Montreal on the grounds that, because of the basic architecture of the engine, it is a reliability issue.
Adrian Newey explained in Monaco that the Renault V8 opens to full throttle when the driver is not pressing on the accelerator due to "exhaust valve cooling".
Reliability aside, Germany's Auto Motor und Sport and Autosprint in Italy claim that the driveability of the Renault engine will also be badly affected by the exhaust blowing ban.
The reports say the 2.4 litre Renault was designed specifically to produce an aerodynamic effect off-throttle, while others have struggled to adapt.
"We lost several engines testing this," confirms Mercedes' Norbert Haug.
Exhaust blowing is a pointless consumption of fuel
Auto Motor und Sport estimates the total ban of exhaust blowing will cost some Renault and also Ferrari-powered teams as much as eight tenths per lap.
FIA president Jean Todt is resolute: "It (exhaust blowing) is a pointless consumption of fuel."
Auto Motor und Sport said the Renault engine is designed to be at open throttle when not accelerating, with Ferrari also at risk of reliability and driveability problems in the event of the ban.
Specifically, Ferrari argues that is opens the valves in that situation to reduce pressure in the crankcase, while Mercedes and Cosworth have an entirely different approach to their valve philosophy.