Today I noticed the old 4 banger that previously had trouble going over the Grapevine to Los Angeles via I-5 (dropped it to 4th gear and revved it out) really had no trouble at all. Seemed like it had another 10-15hp as it climbed it in 5th gear at about 10mph over limit. Only difference was winter gas and maybe the cooler temperatures and high humidity. I understand either the summer/winter gas are reformulated (one is oxygenated and maybe reformed) but the striking HP difference made me wonder.
Any ideas?
BP~