The billions spent behind the scenes in Formula One will make the most significant difference between the teams on Sunday, despite new budget caps aimed at evening the field, race insiders reveal.

A new budget cap for teams introduced last year tightens to $US140 million ($187 million) this year, but the rules allow for 20 different exclusions such as all marketing costs, driver salaries and the salaries of the three highest-paid employees, allowing superstar designers to still make a major difference.