I normally cook around 250 and I foil for an hour. It takes me 3 to 3.5 hours depending on the thickness of the rack. I'm sure it will take longer without the foil. Maybe someone that doesn't use foil will help you more.
2 UDS's /Backwoods Fatboy/ Orion cooker/ 18.5 WSM/ Weber kettle / Cowboy grill