What type of octane I should use??? - Page 6 - Toyota Yaris Forums

mikeukrainetz · 08-23-2006, 06:53 PM

Lower octane gas will fire with less compression, if its misfiring or pinging the gas is lighting up well before TDC, higher octane will bring the flashpoint back up to prevent this. Ive found this really only happens on older vehicles where the timing (among everything else) is old and worn. Carbon buildup can cause this as well. High compression engines (60's-70's and less so 80's and rebuilt hi-po engines) require higher octane to prevent detonation and literal meltdown. What I dont really understand is in the scheme of things the Yaris is a high compression engine - it runs at 10.5:1 and can run on 87 octane... my 70 chev with a built 350 runs 10.25:1 and I cant get away with anything less than 91... it doesnt have aluminum heads but I never understood why one works and the other doesnt....

08-23-2006, 06:53 PM	#1
mikeukrainetz View User's Garage Drives: 2006 Toyota Yaris Join Date: May 2006 Location: Canada Posts: 564	Lower octane gas will fire with less compression, if its misfiring or pinging the gas is lighting up well before TDC, higher octane will bring the flashpoint back up to prevent this. Ive found this really only happens on older vehicles where the timing (among everything else) is old and worn. Carbon buildup can cause this as well. High compression engines (60's-70's and less so 80's and rebuilt hi-po engines) require higher octane to prevent detonation and literal meltdown. What I dont really understand is in the scheme of things the Yaris is a high compression engine - it runs at 10.5:1 and can run on 87 octane... my 70 chev with a built 350 runs 10.25:1 and I cant get away with anything less than 91... it doesnt have aluminum heads but I never understood why one works and the other doesnt....