OTS Tunes (Off-The-Shelf Tunes) are tunes that are made to fit a vehicle without any custom tuning. They are usually meant for a stock car, or a car with very minimal modifications. They are very simple. Just order your tune, flash the file to your car, and enjoy the added power! 

Can I run an OTS Tune on a built shortblock? 
Assuming only the shortblock was changed (no aftermarket head/cam work) In short, yes you can; However, we don’t suggest it. Shortblocks with forged pistons can create difference harmonics within the engine that can trigger false activity from the knock sensors. A custom tune that includes datalogging can help narrow down if and when this is happening. Forged Shortblocks can also sometimes have varying compression based on the pistons used and/or cylinder head machining. A custom tune also allows for overall data review that can be helpful in pointing out minor or major issues that (frequently) arise after a full engine overhaul. 

What about overall power?
OTS maps are going to be more conservative and a custom tune can unlock more torque and horsepower potential from your built shortblock that you normally might not get with a OTS tune.