I should really think about giving up this aviation thing

[Shadrach]

1 hour ago, steingar said:

You wouldn’t notice the loss of a mag in flight. Ask me how I know.

Depends on how you're running. ROP not so much. LOP, the rough running and power loss are exacerbated. In either case, EGTs climb significantly >100df

[pinerunner]

17 hours ago, Shadrach said:

I think you are over estimating the performance loss by quite a bit. Although if your engine has been retimed to 20BTDC you've already taken a hit in climb performance.  Some of the lost performance could be recaptured with proper leaning. Going from a dual ignition to single would certainly cost some power, but not the 45-50% you're suggesting.

I actually did take off on one mag in a J3 cub when I was a student. I'm fairly sure I had checked it but that was just when it decided to fail. It was a 2000 foot grass strip with trees to clear and it sounded different and barely cleared the trees instead of easily cleared the trees. I was really glad for dual mags. 

[Shadrach]

1 minute ago, pinerunner said:

I actually did take off on one mag in a J3 cub when I was a student. I'm fairly sure I had checked it but that was just when it decided to fail. It was a 2000 foot grass strip with trees to clear and it sounded different and barely cleared the trees instead of easily cleared the trees. I was really glad for dual mags. 

Stock J3s in my neck of the woods fly 500' patterns because they barely climb with both mags, so I'm not surprised. I know of someone who departed with a bad mag in a Mooney to reposition to an airport 20NM away with a MX facility. They climbed to 10,500' over the departure airport before proceeding to their destination. Climb performance was more than adequate.

[ShuRugal]

Just use the Harrison Ford standard:  If you start landing on golf courses and taxiways, you might have a problem.  Otherwise, get out and fly!