4 star no longer exists as we know it. it was leaded and then the gouvrnment went all geenpeace on us and if you have old cars like all of our customers your fucked. The valves become coked and it runs like a cunt. But i havnt yet expirienced a cossie on unleaded but i know that optimax and all the others still produced bag performance on old cars naturally aspirated.
Sorry for the lecture
James