bratkozo914 Posted December 1, 2017 Share Posted December 1, 2017 Hey guys, So I have been using my '86 Brat for 40 miles commuting and I just love it. I've got a question for you today. What octane should I use? It still has a stock single carb under the hood. I have been running with the lowest octane(87?) and so far so good. But just realized the owner's manual says 90???? So I need some feed back from you guys. Thanks in advance, bratkozo914 Quote Link to comment Share on other sites More sharing options...
lrgvanman Posted December 1, 2017 Share Posted December 1, 2017 I would say that as long as it doesn't ping or diesel, it should not be a problem but let's see what other folks say. Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted December 1, 2017 Share Posted December 1, 2017 It's an 8.7:1 compression ratio. You can run it on elephant piss if you had some handy. You will get no benefit from octane higher than 87. The rating in the manual is very likely a RON vs. MON issue. Here in the US we average the two ratings while in many other countries they use the higher of the for more better advertising I guess... GD 1 Quote Link to comment Share on other sites More sharing options...
bratman2 Posted December 1, 2017 Share Posted December 1, 2017 It will run better on non ethanol gas if it is available around Oakland. Quote Link to comment Share on other sites More sharing options...
skishop69 Posted December 1, 2017 Share Posted December 1, 2017 Octane rating is the ability to avoid detonation due to compression. At 8.7:1, there is no risk of detonation. I can run 87 octane in my 10:1 SB Chevy 400 on occasion, but if I start pushing it, it gets unhappy if it's hot so I mostly run a minimum of 90. Quote Link to comment Share on other sites More sharing options...
dfoyl Posted December 2, 2017 Share Posted December 2, 2017 The global standard (apart from the US) is RON, as that is the most accurate for daily-use cars. US 87 is RON 91, which is fine. Many modern cars (especially European) require RON 95 (US 91 octane) but I can't think of any Subaru's to date that have RON 95 as a standard ex-factory. If you were running a modified engine (like a 10:1 SBC), you would be better off with 91 octane or higher. Quote Link to comment Share on other sites More sharing options...
bratkozo914 Posted December 2, 2017 Author Share Posted December 2, 2017 Thanks guys for the inputs. It sounds like I should stay with US 87 as I have been using. You folks have a great weekend! bratkozo914 Quote Link to comment Share on other sites More sharing options...
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