Originally Posted by SouthArk370Z

The car will run (see Rusty's comment above) and will, in many cases, run well. Just depends on how far out you are from where the ECM can compensate. The more extreme your mods are, the more likely you are to have a problem. In some cases, you could run lean enough to cause problems. I would avoid WOT until I got a tune.

But you will not be getting the performance you will get with a tune - you will be wasting a lot of potential gains. If you're going to all the trouble and expense to mod both sides, you might as well spend some bucks to make them work together.