I'm sorry I didn't explain myself very well.
I have a friend who is an electrical engineer who designs ECU's for custom and race cars. He's on all this stuff.
Basically all the new diesels, with all the emissions controls to try and make them cleaner has reduced the gap between diesel and petrol. Petrols have a throttle body so suffer from pumping losses. These are now appearing on diesels too. So you use fuel to create a vacuum at low engine speeds. Very wasteful.
That's not so much of a problem in hybrids as they should never really be operating at idle. Small turbo petrols are also smaller and lighter and can be set up to be very economical.

