Impeller

Lawn chipper?? Maybe a Lawn Mower? Like this

More efficient than what?

"how to make a lawn chipper / vac more efficient"

You can make your lawn chipper / vac more efficient by hiring someone with they're own equipment to to take care of your landscaping needs.

Your lawn chipper / vac will not use a drop of fuel.

Try it, you will see!

^{_{(Sorry - couldn't help myself, I'm off to the bad boy corner now)}}

If the lawn is big enough buy a goat. The lawn is the fuel. No need to vacuum. The roses grow better with the recycled waste.

(Make room in the bad boys corner)