The teams are no longer allowed to use qualifing engines and then change to their race engine in an effort to reduce cost. The old method was to build an engine that was milked for ever 1/10 of a HP they could find. The truly amasing fact was how close they knew to the very lap that it would explode at a given HP. So build it for every tiny bit of HP available for say 5 laps or a little less HP if they needed it to live for 10 laps.
These builders were cutting the inner beams out of con. rods, cutting center out of the rod throws on the crank, reducing pin walls to the min. and cutting piston domes until paper thin and so on. Then running
oil vescosity so thin it would sieze engine if not heated before starting engine. THEY ARE GODS of the HP world now forced to build engines that they have to make live for practise, qualify and then the race all with the same grenade.