It would be none of those and de-restriction is very rarely that easy anyway. Restriction is mostly caused by physical means. Things like restricting the size of the fuel inlet ports to the engine and the exhaust ports from the engine...
2 Answers · Cars & Transportation · 29/10/2020
The Honda .
2 Answers · Cars & Transportation · 19/04/2020
Car engines and large motorcycle engines can have their cylinders bored out and have oversized pistons installed. Also, it's possible to gain a little extra displacement with a different or modified head...
7 Answers · Cars & Transportation · 11/09/2020