Hi guys just wondering anyone knows how the taxation rules go ? if you have a pre 1992 under 1597cc car which would currently be about £134 per year and fit an over 1600 cc engine does tax class change or remain as original ?

DVLA require you to notify them of any changes, and yes this would take you into the higher taxation class when you told them.

You "could" also be required to take the vehicle for an inspection, but this doesn't always happen. (If it was POST 2001 they almost always need an inspection, although strangely they very rarely change the taxation class as proving the CO emmissions would prove too costly).

You will also need to prove to them where the new engine came from (which can be fun), basically it's a big can of worms if you haven't done it before, just make sure you keep receipts for EVERYTHING, they love a paper trail.