Clio 197 destructive misfire

Hi all can someone shad som light on this.
My clio was a running car.
I fitted 12.7:1 comp pistons and 402 cat cams.
Car starts fine and rev clean when stationed.
But the minute I drive it 1km or less MIL light starts flashing and when I read with clip it says Distructive misfire.
No other faults are present.