Benefits of 91-93 octane ?

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4,353
Location
FL
I have a 04 civic. In the manual it says that i could use 86 or higher octane gas. Lately I have been putting in 93 octane because it feels like it has a very,very,very slight difference in power and it seems like it is less noisy than 87 octane (could be psychological). So I was wondering if there were any benefits of the extra dollar or two that I spend each fillup or am I just wasting my money? Any adverse effects?
 
Messages
889
Location
MI
Your wasting your money. Only use more expensive gasoline if your engine is knocking. My has 90k Miles and I have been using regular.. my car is in top knotch condition still. especially on a Civic.
 
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189
Location
Raleigh, NC
For your car, waste of money. For a corvette is not a waste. Your car is MADE to run on 87, a corvette (or other high compression engine) is made to run off high octane.
 
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43,667
Location
'Stralia
depends entirely on the engine management system. Some systems can make good use of the higher octane. Some can't. My 4Runner (91RON specced) gets significantly better mileage on 96RON fuel...enough to pay for the cost. My (former) camira was a simple speed density system that gained nothing with higher octane.
 
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21
Location
Addison, Texas
Each engine is different. My pickup while specced for 87oct gets enough better fuel mileage with 93oct to justify the cost as long as the price difference is less then aprox 25 cents. You won't know what's best for your vehicle until you run fuel mileage logs for both fuels. And remember it can take your car's ecu some time for it to adjust itself to take full advantage of a higher octane fuel.
 
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1,979
Location
Houston
The easiest relative term to determine if higher octane might help is the compression ratio. Typically engines under 10:1 can use 87, over 10:1 may need a bit more. Your Civic is either 9.5, 9.8, or 9.9:1 . What adds confusion is some higher-compression engines have knock sensors (Toyota v6 as example), so while the engine may normally want to ping on 87, the sensors adjusts the timing so that it never happens. It runs fine, albeit with slightly off timing, on 87. Power does suffer altho many can't tell it. My camry (97 v6) states: 87 is required, 89 or higer for increased performance (or words to that effect). Yes, it does make a difference, it is 10.5:1 (in the v6 only). But a good compromise for me is the 89 /midgrade. It's enough to see some noticeable power gain, but only a 10c/g hit instead of 20c/g for 93.
 
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113
Location
Erie,PA
I'm still learning a lot here. I have a question about 'high compression' engines. My Prius 1.5L 4 cyl. has a compression ratio of 13.5 to 1 but the manual specifies 87 octane gas. It runs very smooth and I use only 87 octane Shell gas. Do you think there would be anything to gain by using a higher octane gas in this engine?
 
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1,979
Location
Houston
Well, since it's a hybrid, I'm not sure if the regular theories hold. With only 82 HP, any increase would surely be noticeable. I don't think Toyota was marketing the car based on HP, so I can see why they don't recommend anything other than 87. At 13:1 and 87 octane, the knock sensor is obviously doing a good job. Having a car that saves fuel but needs higher octane fuel would be a marketing nightmare.... but it won't hurt to try a tankful or 2.
 
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625
Location
Silver Spring, MD (USA)
Hit up the honda forums. The 03 6spd V6 Accord coupes actually see a 10 whp gain in performance when switching to premium. Though the engine specs 87 octane, the knock sensors and computer adjust the timing when it detects the premium gas, and increases engine performance. However in most new vehicles (older OBD-I cars not included) this is NOT the case. The engine doesn't have the capability of detecting the higher octane gas, and uses the same timing setting as per the 87 octane gas...and you LOSE power. Of course with all these stupid movies of late, the general populace is under the impression "more is better, bigger is better, giant wings add downforce!!!", which isn't true at all, but because of the market saturation of such advertising, a placebo effect normally occurs when putting in higher octane gases. The only way you'll know for sure is by visiting a model specific forum and finding a before/after dyno. The Mazda 6 (2.3L I4 and 3.0L V6) both lose power on 93 octane, as well as creating a more inefficent combustion, which results in excess fuel being dumped into the precats. Oh boy.
 
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39,805
Location
Pottstown, PA
quote:
depends entirely on the engine management system. Some systems can make good use of the higher octane. Some can't.
That's about it. The reason that you've heard "don't use premium because it will do you no good" rhetoric is because fuel refiners were giving the impression ..actually an extension of the REAL use of premium when all the Euros spec'd premium for their fuel injected engines (late 70's and a while into the 80's) since ONLY premium had the additives that the Eruos needed (they were about the only injected engines ..and they also spec'd premium). This constructed a myth that premium fuel was "better" for your engine. Exxon had to pay a big penalty for passive advertising that implied that their premium "helped" your engine. This caused a major "backlash" in corrective advertisement that has kinda constructed its own "mini-myth". Just because it will not "benefit" your engine in longevity or reliability ..doesn't mean that performance/drivability gains can not be realized under certain conditions. As was said ..it all depends on the fuel managment system/engine. My late mother's Corsica with the simple 2.0 liter engine ..when it was hot and the ac was on ...couldn't get out of its own way under our rolling hill environment ...frequently needing a kickdown to conpensate for the added load. The use of premium relieved this condtion. Did it give it better gas mileage? Not according to my calculations ..but it did improve drivability. Granted this was an OBDI system (86). In our 99 jeep 4.0 ..it only relieves the light knocking that you hear during accelleration. It doesn't "pull" any better ..it doesn't get any better gas mileage. [I dont know] In my 2.5 jeep ..using passing gear under hard throttle results in the engine sounding like it's a coffee can full of bb's ..premium relieves this condition and you get a smooth pull up to the rev limit/governor. Do I use premium? No ..I just don't run it to the redline on a regular basis. It doesn't get me anywhere fast anyway [Big Grin]
 
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2,187
Location
Arizona
quote:
Well, since it's a hybrid, I'm not sure if the regular theories hold...
Correct.
quote:
...the knock sensor is obviously doing a good job...
Well, yes, but misleading. That engine is a very high swirl design, and I believe it's a VVTi engine. It's designed to run very efficiently even at part-throttle. High compression ratios (not the same as high compression) help increase cycle efficiency when cylinder filling rates are low (low throttle openings). Valve timing also comes into play to reduce total compression (not ratio) under high load to prevent pre-ignition.
 

Kestas

Staff member
Messages
13,959
Location
The Motor City
quote:
Originally posted by bulwnkl: That engine is a very high swirl design, and I believe it's a VVTi engine. It's designed to run very efficiently even at part-throttle. High compression ratios (not the same as high compression) help increase cycle efficiency when cylinder filling rates are low (low throttle openings). Valve timing also comes into play to reduce total compression (not ratio) under high load to prevent pre-ignition.
Your statement kinda begs the question, 'if this design is so efficient, why aren't all engines made with this very high swirl design?' There has to be a downside to this technology.
 
Messages
4,844
Location
Saskatchewan
quote:
Originally posted by pa04prius: My Prius 1.5L 4 cyl. has a compression ratio of 13.5 to 1 but the manual specifies 87 octane gas. It runs very smooth and I use only 87 octane Shell gas. Do you think there would be anything to gain by using a higher octane gas in this engine?
It may not even be relevant to compare it to compression ratios of traditional engines because it is an Atkinson-cycle engine. http://en.wikipedia.org/wiki/Atkinson_Cycle Whether you would see any gains from premium fuel would depend on whether the computer can and does advance spark timing to take advantage of the extra octane. But if the owner's manual doesn't mention anything about higher octane being beneficial, then it likely isn't. My buddy's T/A's owner's manual, for example, says that you can run 87 octane instead of 91 but with reduced performance. [ March 04, 2005, 02:02 PM: Message edited by: rpn453 ]
 
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1,979
Location
Houston
ah-HAH! ".....because it is an Atkinson-cycle engine" that explains the 13:1 ratio.....it sounded like some late 60's GM muscle with those #s. nice link, thanx.
 
Messages
113
Location
Erie,PA
Thanks for all the input. I'm learning more and more as I go on here. Considering that they just said on the news that gas prices may jump $.25/gal. in the next week, I don't think I'm going to try the higher octane gas any time soon, though if I could go from 45 mpg to 50 mpg I might be tempted...
 
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