Bit of a technical question here but I’m perplexed how two engines with the exact same piston diameter/ stroke can have such different compression ratio’s (one for N/A one for turbo charging)  which in essence are the exact same engine also doesn’t make sense what does everyone think dished pistons ? 

Different volumes of combustion chambers in their respective heads?

Nah, it's piston crown, dished or flat for turbos, raised for N/A, 4V pent roof chambers on modern cylinder heads have no scope for varying the volume.

Cheers for the reply guys so my question is , what’s stops you using the crankshaft / conrods from a 1.6 FSI into a 1.4 tsi bringing it to a 1.6 TSI (with the turbo pistons) as the block and heads are essentially the same , could potentially even use the 1.6 FSI camshafts for an all round  better engine 

Block deck height will almost certainly be different due to the longer stroke of the 1.6, so there's that...

28 minutes ago, sepulchrave said:

Block deck height will almost certainly be different due to the longer stroke of the 1.6, so there's that...

I thought the crankshaft dealt with the longer /shorter stroke so the 1.4 crankshaft will just have the piston go less down the bore whereas with the 1.6 FSI crankshaft / conrods combo will go further down the bore similar to what the rover did with the k series engine same block / head different crankshafts and rods 

24 minutes ago, thomasaspin said:

I thought the crankshaft dealt with the longer /shorter stroke so the 1.4 crankshaft will just have the piston go less down the bore whereas with the 1.6 FSI crankshaft / conrods combo will go further down the bore similar to what the rover did with the k series engine same block / head different crankshafts and rods 

 

The additional bore length required is double the stroke, my educated guess is that the pistons would stick out of the top of the block.