I need a motor for my formula I would like a 3.1. If any one has purchased one please let me know your story good and bad.

I took the 2.8 out with a bad rod knock. I put in the rebuilt engine as a 3.2. total investment was right arround $2000 or so. true I could get a 3.4 crate for $1650, but then you start adding in things, and it'll shoot up higher. if I had it to do over again, and was planing on doing it (instead of, only means of transportation goes knock knock knock). I would have saved up an extra grand and gone for the 3.4 install. just to make sure I had enough to cover what ever happened.

what would a 3.1 brings the horsepower up to?

it all matters on the cam. If you go for high flow exhaust, and either headers or open up the manifolds, with a strong cam, I can see you pulling 200 hp at the flywheel. I built mine to be more on the torque side. so I should be arround 175 hp, with arround 205 ft lbs of torque at the flex plate, stock exhaust an all.

The major benefit of stroking a 2.8 to a 3.1 is in the additional torque. Don't get hung up on HP numbers.

My daughter had an 86 RX7 which was rated at around the same hp as my 2.8 but the torque sucked.