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bratkozo914

Octane Rating for our Brat

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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

 

 

 

 

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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

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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.

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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.

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