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Recommended Octane and rated HP

Bruce Nunnally

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I was reading a summary of changes to the SAE standard J1349, the measure of engine hp, that closed off some loopholes that manufacturers previously had abused.

One loophole that got closed was that the octane of fuel recommended for the car has to be the octane of fuel used in the test. So, my theory now is that while the Northstar V8s since 2000 and 2.8/3.6L V6 VVT engines can use regular or premium fuel and adapt just fine, Cadillac changed their wording on the octane recommendation toward requiring premium fuel in order to continue to use the higher octane fuel for engine hp testing. Sure, it may only be a 5 or 10 hp hit, but better to be able to advertise the higher hp you can attain with the higher octane than vice versa.


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Indeed, this is amazing because the HP split between regular and premium fuel is 'only' 10 HP. This can be attributed to the engine controls system that pervades many of today's cars.

I read that the loophole was closed some time ago (1 year? 2 years?). Now only if they would be more realistic in the EPA mileage ratings.

I'm in this field (I'm an Electrical Engineer - embedded systems and controls) so this is particulaly fascinating to me.

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