Higher octane than recommended a waste?

[edyvw]

Like everyone else said, depends on manufacturer.
Most engines do not require premium. Most Euro gas engines do, although there is an attempt today by VW to allow 87-93 octane rating. However, they state that peak power is lost.
Mazda in CX-9 explained it best. If you use regular engine makes 227hp and 310lb-ft. If you use premium, engine makes 250hp and 310lb-ft. So benefit is in high rpm. Now, most American buyers buy HP, but actually they love torque. So Mazda basically said: yeah, in CX-9 soccer moms will mostly use low-mid range rpm, so why bothering with premium if you do not use high rpm. If you do (and most drivers of CX-9 do not) then just put premium.
Now some manufacturers are pretty strict on that and BMW, MB and some others are pretty strict on minimum 91.

 

[Danh]

It seems some DI engines enrich the mixture in addition to/instead of pulling timing when knock is detected. If you have one of these, higher octane may reduce fuel dilution. This may only occur in certain conditions (e.g. highway cruising into a stiff headwind, trailer towing), but a few extra dollars per fill up may be worthwhile.

 

[nthach]

Originally Posted By: Danh
It seems some DI engines enrich the mixture in addition to/instead of pulling timing when knock is detected. If you have one of these, higher octane may reduce fuel dilution.


One of the main selling points of DI is to achieve "lean burn" under more conditions - but the mixure will always be richest near the spark plug/injector area. I think I've seen a Toyota white paper on D4-S showing the thermodynamics under most driving situations.

 

[lenjack]

placebo effect

 

[BironDanmum]

It depends entirely on your vehicle. If your knock sensor advances or retards timing based on the fuel, then yes, you'll see better performance running premium fuel.

What's ignorant on both sides of the debate is when one person issues a blanket statement as if there's only one type of car sold and what's good for that car goes for all other cars in the country/world. That's what irks me about all of these so-called "exposé" investigations done by scare-the-old-people "journalists" who interview some yokel that owns his own mechanic shop and present him as an expert on fuel. "Yup, I say don't run no premium in your car cause it don't help none and you're just putting money into Big Gasoline's hands cause Illuminatti."

So investigate whether or not your car can take advantage of premium fuel and stay away from blanket ideologies and statements.

 

[L_Sludger]

Car & Driver did a great article back in 2001, with dyno graphs comparing high octane to 87 octane for a variety of vehicles.
One unexpected result was that a vehicle - a Honda Accord - actually LOST horsepower on the 93 octane test.
Quote:
The Accord took a tiny step backward in power (minus 2.6 percent) and performance (minus 1.5 percent) on premium fuel, a phenomenon for which none of the experts we consulted could offer an explanation

Their online version of this article is missing the dyno graphs but it is still a great read!

http://www.caranddriver.com/features/regular-or-premium