OK let me try this

HmMmM . . . if you know how a four stroke engine works, you will know the compression happens when the piston move up from bottom deck center (BDC) to the top deck center (TDC) of a compression stroke. This compression stroke compress the air/fuel mixture in the cylinder hence increase the pressure of the mixture. During the compression, temperature rises.

For N.A = since air is not precompressed, you can compress it more without it being ignited by the high temperature which is call detonation which may cause knocking which is bad

For T.C = since the air is precompressed by the turbo charger which has high pressure hence high temperature :dunno: . If you compress it alot in the cylinder again, it will cause it to pre-ignite by over heat and cause detonation.

did i missed out anything lets wait for the expert here to fill things out :naughty:

for N.A. B18C1 will be faster then B20Z (stock to stock) and B18C1 have higher compression ratio :dunno: As its natural for a bigger displacment engine to have bigger torque . . so which is faster actually ? ? ? expert please ? ? ? heehee

for Turbo Charged, B20Z allows more boost as it has lower compression ratio :dunno: