Nope.

The price tag...

Haha, that's true, but nope, not what I am after...

the body of the car?

Nope. Here's another hint, it's the part of the car that makes something bigger, not a part of the car that has been made bigger.

DPF, makes repair bills bigger?

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Airbags

Good answers but nope

Fuel pump? They run bigger pressures these days...

Tyre inflation pack

Nope.

I could offer another clue if you require ir

I think that would be useful yeah lol.

Something I serve should shine, and should not be dull

Spoiler

Nope

Headlights. Hid?

Brakes, Discs or pads.

gear box? or gear stick

None

the top speed ? the engine cover the entire engine? exhaust? the boot ?

Nope.

Ok so to summarise, I make something bigger on modern ford's than I did on the old, comparing to cars about 15 years old, it's a part or system of the vehicle that makes something bigger, as opposed to a physical part of the car that has been enlarged over years. Finally, I serve something that should shine, and not be dull.

Headlight projector

Ballast

Battery

Turbo

Ecoboost

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Cams or variable cam timing (that's relatively recent isn't it)?

It kind of serves something that should be shiny i.e. the inside of the cylinders / pistons. Makes the valve openings bigger when they need to be, well that's as far as my limited logic will take me :P