<full disclosure - I don't have personal experience with this rocket. But I can show you some tools you can use to make some educated guesses about safe motor rocket combinations>
Like most things in life, it depends...
Can I assume you got a Super DX3 - 4 inch airframe, 38mm motor mount ? The catalog weight is 44 oz. To stay under the L1 limit the easiest thing to remember is your motor can't have more than 80 newtons average thrust. So you'll be looking at motors like the Aerotech G80 White Lightning, G77 Redline, or G76 Mojave Green. You'll probably want the shortest delay available because a rocket with this mass will slow down relatively quickly when the thrust of these motors cut out. Also you'll need a 29 to 38mm adapter to fly with these motors
So, I would first take a look at the flight logs on Rocket Reviews to see if others have recorded their flights:
https://www.rocketreviews.com/madcow-rocketry-super-dx3-by-mike-caplinger.html Base on that info it looks like some low and slow flights can be had with those motors.
Next I might look at the motor guide page on thrustcurve.org. You can get a ballpark list by typing in the vital statistics of a rocket there.
Lastly you could download the rocksim file from Madcow and run the sims for different motors to see which ones would be safe.
Of course there's no substitute for real world experience and I'm sure some DX3 owners will see this and respond with their thoughts.
