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Old 04-13-2015, 12:07 PM   #11
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I simply will not buy a vehicle which requires premium.
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Old 04-22-2015, 11:22 PM   #12
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Octane needs depend on engine compression

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Originally Posted by andyrobo View Post
Octane stuff is kind of cool. This is the best article I found that describes what Octane does:
Octane Ratings

So octane needs depend on the compression of the engine. It looks like your bike has a fairly high Compression Ratio of 11.3:1
Total Motorcycle Website - 2005 Suzuki DL1000 V-Strom 1000

This would suggest that even though your bike has proven to run on lower Octane, as you pointed out, you will indeed see better performance with higher octane because your engine design (compression) is high enough to take advantage of a higher octane.

One thing to consider is the performance increase vs the cost increase. If the fuel economy increase is 5% but the cost of higher octane is 8% then maybe it's not as economical (of course better fuel economy is kinder to the planet and higher octane might perform better).
Here's a dilemma for the statement that "octane needs depend on the compression of the engine."

Both of my Ninja 900 sportbike motorcycles have 12.2:1 compression ratios. They mostly run 87 AKI, a.k.a. 87 regular unleaded. By mostly, I mean most of the year that's what I put in them. They do not ping. They'll pull redline every time I ask them to. Neither does better or worse on MPG using 87 regular, 89 mid-grade or 91 premium, which is why I mostly only fill them with 87 AKI. One of them is closing in on 88,0000 miles. And their fuel tank range performance is so exceptional, they're outrun most touring bikes.

The dilemma is not a trick question, but points out the oversimplification of recommended octane ratings, especially as it relates only to compression ratio. The answer to how my two high compression sportbikes are able to run 87 AKI happily, shows that octane requirements don't come down to one factor, but instead many factors. And once you understand what those factors are, you'll emphatically know what grade of fuel you can run in your vehicle regardless of what the manufacturer recommends.
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Old 04-23-2015, 04:25 AM   #13
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There is more to "compression ratio" than meets the eye. "Compression ratio" and "expansion ratio" are mechanically identical, being the ratio between the total cylinder volume (combustion chamber plus swept volume) and the combustion chamber volume. The expansion ratio is the part that determines engine efficiency; the compression ratio determines fuel requirements.

And then there is "effective compression ratio" and "effective expansion ratio." Compression cannot begin until the intake valve closes; expansion ends when the exhaust valve opens. Low speed engines usually have only a little valve overlap, so the effective ratios are pretty near the mechanical ratios. High speed engines, such as sport bike engines, usually have a lot of valve overlap because they need it for engine breathing. Early exhaust valve opening reduces engine efficiency and increases noise, but gets exhaust flow going sooner for better air exchange. Late intake valve closing allows better cylinder filling at high speed, but reduces compression ratio and incidentally reduces octane requirement.

I have never tried this, but I am told that a good way to win bets is to take a compression gauge to a motorcycle breakfast and bet folks that a touring bike such as a Gold Wing will have higher compression pressure than a sport bike such as a Ninja.
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Old 05-02-2015, 10:29 AM   #14
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Besides valve timing. There is a throttle valve. The only time you reach high compression numbers is with open throttle valve. So your choice of fuel can vary with your own personal usage of the throttle.
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Old 05-02-2015, 07:31 PM   #15
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Lots of octane stuff on this thread. What about 87 octane 10% ethanol blend(E10) vs. 87 octane ethanol-free gasoline(E0)? First, 87 octane E0 has its molecules averaging 87 octane....(duh!). But, 87 octane E10 is widely different. First, the 10% ethanol molecules are 114 octane, wildly outside the 87 octane recommended for 87 octane, low compression ratio(9:1 to 11:1) gasoline engines. Second, the octane comprising the remaining 90% ethanol-free gasoline molecules average.....drum roll, please, 84 octane.....to off-set the 114 octane ethanol! Yes, even the gasoline molecules are outside the parameters of the 87 octane gasoline engine. If your car is knocking or ain't performin' on 87 octane E10, try 87 octane E0.....& pick up 3 octane points.
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Old 05-04-2015, 05:45 AM   #16
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Quote:
Originally Posted by Charon View Post
I simply will not buy a vehicle which requires premium.
+1

I wont buy a diesel either as the price/gallon tends to be significantly higher than 87 octane regular here in the US.
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Old 07-03-2015, 06:06 PM   #17
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Neither does better or worse on MPG using 87 regular, 89 mid-grade or 91 premium,
only once in 120,000 miles have i gotten same exact mpg, twice in a row.
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Old 07-05-2015, 11:24 PM   #18
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only once in 120,000 miles have i gotten same exact mpg, twice in a row.
Congratulations?
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