As big as a 7.0L Olds as small to a 1.8 turbo VW. it depends what kind of vehicle you are trying to move. Personally I prefer a smaller engine that likes to rev and returns better mileage.
My most fun vehicle only has 650cc's and it will get me to 60mph in 4 seconds flat and gets 50mpg. Although, it also only has 2 wheels so it's tough in the snow.
