8.6secs in a Civic 1.8L MT is achievable, the 0-100 run depends on various factors.
Here's how you do it: Achieve a perfect launch with a perfect shift into the 2nd gear at the right rpm on a grippy road with some high octane in the tank and im sure your civic would shave off a 0.5sec or more but since these are ideal conditions one barely meets them.
Bad_Cheetah's civic is very fast, I have experienced it myself. His cars engine is in very good shape so are the tyres and the clutch plate. We did make a video of the car doing 0-100 in 8.6secs but I prefer not to post it here as Bad_cheetah has already stated the reason.
Since you yourself have claimed that you did it in 8.9secs then I don't think 8.6secs shall be a problem to believe in unless he's claiming 7.6secs on stock conditions, yes I too would doubt in that case.