I need to cook a 9 pound pork roast in a crock pot/slow cooker. How long do I need to cook it? I have a recipe for a 3-4 pound roast; is there any way to adjust it for a larger roast?
TL;DR: Never use cooking time as a measure for meat doneness.
Why? Well it's pretty simple. According to the CDC:
What is trichinellosis?
Trichinellosis, also called trichinosis, is caused by eating raw or undercooked meat of animals infected with the larvae of a species of worm called Trichinella. Infection occurs commonly in certain wild carnivorous (meat-eating) animals such as bear or cougar, or omnivorous (meat and plant-eating) animals such as domestic pigs or wild boar.
There is no accurate way to know the doneness of your large roast judging by the time. With scary infections like Trichinellosis you don't want to risk it for your family.
Invest in a meat thermometer! You can get a digital thermometer at most grocery and general stores, and online. They are inexpensive, many read temperature practically instantly, and some types you can even leave the thermoter in the meat while it cooks. Those normally have a digital display that is connected to the thermostat probe with a heat-safe wire.
Again, according to the CDC page above:
For Whole Cuts of Meat (excluding poultry and wild game)
- Cook to at least 145° F (63° C) as measured with a food thermometer placed in the thickest part of the meat, then allow the meat to rest for three minutes before carving or consuming.