If you take 2 mm of the top on the pistons or put 2 gasket between head and block you won't change the stroke or displacement. You will change the compression. I have calulated on it now... If you take 1.3 mm of the top, or put an a larger gasket in (1.3 mm + orig. gasket) you will lower your compression from 9.6:1 (4E-FE) to 8.2:1 (4E-FTE). So if you hold the pressure on 0.6 bar the engine will hold as a turbo engine. If you will displacement tune your car you have to install other rods, and crankshaft, up drill your cylinder to get a large bore. Change the pistons so they fit the new bore, and be sure to get them so they get an higher compression. change the gasket and put a lower gasket between head and block. Compression is now about 11:1 and a displacement approximately on 1400 ccm. Then you can change the intake with 4 trottle bodies, then change cams, value, valuespring and blah blah blah. This is the NA way. But this is much more expense way of tuning...