The factory - rated 385 HP was achieved through a larger turbocharger unit, increased boost pressure, modified cylinder heads with larger inlet and exhaust ports, re-profiled camshafts and advanced valve timing. (dupontregistry.com)
Compared to the GTI's powerplant, the Golf R's engine has a modified cylinder head, exhaust valves, valve seats and springs, pistons, injection valves and larger intercooler and turbocharger. (en.m.wikipedia.org)
It is distinguished by the different pistons (compression ratio of 13) and a modified cylinder head. (mywikimotors.com)