Why do I have less power in my Honda Accord with a higher octane gasoline?

[MinnesotaNole]

1994 Honda Accord EX (Aprox. 96K) 2.2 L VTEC 4 banger

I like to experiment with different brands and octanes of gasolines. I recently put in 90 octane Super Unleaded from Cenex and my car seems more hesitant with less power (although it idles somewhat smoother)

I used 87 octane from Amoco before the Cenex fill and my car ran outstanding. Much more pep and power.

My owners manual calls for any gas with an octane of 86 or higher. It doesn't say I have to use 87 octane gas or that my engine runs best with 87.

This also has been the case before. 87 octane from one station usually runs better than 89 octane from another station.

It seems like my engine runs best with 87 octane gas. What's the deal here? Why wouldn't it run better with the higher octane gas?

[ August 23, 2003, 06:11 PM: Message edited by: MinnesotaNole ]

 

[MRC01]

quote:

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Originally posted by MinnesotaNole:
I like to experiment with different brands and octanes of gasolines. I recently put in 90 octane Super Unleaded from Cenex and my car seems more hesitant with less power (although it idles somewhat smoother)

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The octane rating measures only how well the gas resists detonation. Octane has nothing to do with energy content of the gas. Most engines run best with the lowest octane that doesn't ping. If the engine is not designed to require high octane gas, there is absolutely no benefit to running it. Your car is probably designed to run 87 octane gas.

OTOH, modern cars that require high octane usually have a knock detector so if you put 87 in them it won't break anything but you'll lose power & efficiency.

Finally, seat of the pants comparisons on power are hugely inaccurate. Any difference less than 10% is pretty much impossible to discern with the butt-o-meter. The only reliable way to get accurate and comparable measurements is to use an accelerometer or a dyno.

 

[MNgopher]

If you bought both tanks of gas in North Dakota, I bet the answer is simple.

Minnesota state law mandates all gasoline has 10% ethanol in it. I don't believe North Dakota is the same.

Another use of ethanol (other than pollution rduction) is as an octane booster - mixed in a 10% blend with 87 octane gasoline, you get a midgrade 89 or 90 octane gasoline.

Cenex is a farmer owned co-op that produces a significant amount of ethanol amd a significant portion of its membership are corn farmers.

My bet is your 90 octane super unleaded is a ethanol blended fuel, whereas you regualr 87 octanes are not (except maybe at Cenex

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