Is there a way to create one new database that will always use InnoDB while the other older databases will remain unchanged and will use MyISAM?

Running both Drupal 6 and 7 and the new one is a snail, so I want to try and crate a new InnoDB database and see how it goes, but am unsure of what to exactly do. Cheers for any helpful comments or pointers in the right direction!