Without boring the block or paying for an oversize block, the next change which works extremely well with the ZX-11D camshaft grind, is to put in aftermarket 12:1 or 12.5:1 pistons. Wiseco makes them. Mahl is another. I'm sure the UK and Europe has plenty of great companies for this stuff. This final change, which is a bolt in and usually doesn't require any honing (Nikasil bores), just a patient "break-in" will raise net rear wheel HP of 150 HP up to 160 HP when finely tuned. [links]