We're using our electric smoker to do 2 pork loins close to equal size. We did only one loin before and it was great!
Do we need to adjust the time and or temp to do it right again? We want to do them together.
We are using the "Masterbuilt" brand smoker.
When smoking pork loins (or anything else) it is best to focus on the internal temperature of the meat as the measure of 'doneness' with time and temp as a loose guideline.
Another good point to remember is that if you are smoking at more than 250F your meat will 'coast' (continue to cook after being removed from the heat) for a good deal longer than if you cook it at less than 250°F (120°C). At greater than 250°F you will see an increase in internal temp of 12-18°F (~10°C) after the meat is removed, at under 250°F it is only likely rise 2-4°F (~2°C).
Because you're working with a greater volume of meat, when you put it in, it will take longer for the smoker to get back up to working temperature, and it may be quite a while before the overall temperature in your smoker is where it needs to be. If your smoker doesn't auto-adjust its cooking temperature (turn itself up temporarily), then you can assume it will take longer to cook both loins properly.
Increasing the temperature of the cooking overall can help with this, but you do run the risk of making the outsides of the loins more cooked than you want.
One of the advantages of low and slow cooking is that the meat, even a large cut, can be more uniform in temperature throughout, rather than especially done on the outside and rare in the middle. If you turn up your temperature to make up for the extra meat, you will be casting some of the low and slow advantage aside.
My choice would be to use the same temperature you did before, but cook it longer. You'll eventually make up for the extra thermal mass of the meat, and you'll still have the advantages of slower cooking.
As Cos Callis said, you'll do well to use the internal temperature of the meat as your guide to how much longer you should cook.
Rule number 1 of smoking/barbecue: Don't try to make the meat come out at a specific time. It needs as long as it needs, and there's very little you can or should do about it. If you're on a deadline, start early enough that you're certain to be early with the meat, then hold it at temperature. Much better results than rushing it.
Get a probe thermometer for each pork butt or at least one which you should put in the thickest butt and go by that. Set smoker to about 225-240, and just let it take as long as it needs. Take the butts out at an internal temp of 195. I've got the Masterbuilt digital smoker and have done 4 at once, so two won't be any trouble, just go by internal temp.
