Whatever happens you know that trying to police it will be impossible especially the big manufacturers. If Engines are in the cap then I would imagine the conversation going like this:
"Hello Mercedes High Performance Engine's, this is the Mercedes F1 Team, we have 20 million dollars in our budget cap left to spend on a new engine, how much will a new engine cost?.......... 20 million dollars, well thats a stroke of luck, thanks, goodbye"
"Hello Daimler AG, this is Mercedes High Performance Engines, we've done that work you asked us to do on Project F... errr we mean Project X, wink, wink, and the total bill came to 480 million dollars. We're sending the invoice now"
"Hello Mercedes High Performance Engine's, this is the Mercedes F1 Team, we have 20 million dollars in our budget cap left to spend on a new engine, how much will a new engine cost?.......... 20 million dollars, well thats a stroke of luck, thanks, goodbye"
"Hello Daimler AG, this is Mercedes High Performance Engines, we've done that work you asked us to do on Project F... errr we mean Project X, wink, wink, and the total bill came to 480 million dollars. We're sending the invoice now"
