Just been thinking abit - all the DOHC extractors ive seen fitted to engines in AUS are similar in design to SOHC engines. I wonder how much better this would be for top end flow...
Project One - 1976 TX Gemini Coupe G200z Turbo
Daily - S15 200SX, 13.29 @ 107mph
i saw them a while ago. there bloody nice. i think if you had a set of extractors like that on a single cam it will have better top end then most the ordinary one's i see getting around. probably $600 to get a set made or more.
probably save half an hours labour and a couple bucks in material. ive brought extractors done like yours for $50 second hand the extractors i have now are worth about $500 but work well.