Re yeasting?

I made a coffee porter and sg was 1..081. i racked at 5 days later. Sg was 1.028. Could i achieve a lower sg if i pitch more yeast?

Maybe. Why did you rack after 5 days. Don't do that. Certainly don't do it until you check gravity and then definitely don't do it if gravity isn't where you think it should be. Next time don't pick at it. No way a 1.081 beer is done fermenting in 5 days or even 2 weeks for that matter. Not to get into this debate again, but I haven't racked to secondary since I discovered it was basically worthless. Very few legit reasons to use a secondary at all, and now you are finding out the damage it can cause.

If you followed a recipe correctly and you think there are still fermentable sugars then give it another week. If it still hasn't budged you could add more yeast, but chances are you got enough yeast in secondary to finish the job if there's a job to be finished.

what temp are you fermenting at? If you're hoping for more fermentation, you might want to warm the wort 5-10 degrees if you don't go beyond the recommended range.

The beer made a come back!! It took 6 weeks in the bottle but it is one of the smoothest beer I have ever had! I am going to enter in a homebrew contest in August.