The Estate is a what American call Station Wagon.
A station wagon
The same part the British call the bonnet.
The bonnet is what Americans call the hood of the car.
Because the only reason you needed a car that large (or so the marketing people would have us believe) is that you have a country estate.
station wagon
A car.
A "Bonnet" is the British equivalent of a "hood". There are several differences between American and British automotive terms. Other translations include "boot" which we Americans call a "trunk", "propshaft" which we call "drive shaft", "drive shaft" which we call "axle", and "spanner" which we call a "wrench"
boot
BONNET A Bonnet
You answered your own question.
I think we just call it exhaust. However, environmentalists call it pollution or green house gas! : )