Originally Posted by mercfocus

Preheating makes the sleeve expand and that's how some of the pinch is relieved. The main thing about preheating is it brings the engine up to operating temps. This is especially helpful on unbroke engines because when you're trying to run it when it's still too cold, it most likely wants to die. The needle settings are giving it more oil so it will struggle cold.

I use Compitition Heat preheater and a foam sleeve over the head to help keep it from cooling while my HSN and LSN are set extra rich while driving it.