The 8-valve GTI engine seems to produce anywhere from 7-8 more hp all the way up to ~5700rpm, where it finally gets overtaken by the 16-valve GTI engine. The latter is very superior to the 8-valve between 5700rpm and 7000rpm, which undoubtedly reflects why most racing categories e.g., Formula One, LMP, MotoGP, prefer 4-valve or 5-valve (where permitted) 4-stroke piston engine layouts.
However, the 4-valve Supercars runners always had the option of fitting smaller valves (& smaller ports) to improve torque and increase port velocity, and in Todd Kelly's series on designing their Ford racing engine he seemed to give the impression that Kelly Racing had designed their 2-valve combustion chamber to fit the biggest valves they could, likewise he gave the impression they had opened the ports up a lot too. So that seems curious.
Last edited by V8 Fireworks; 12 Sep 2021 at 19:21.
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