Originally Posted by Staninator

It's highly debatable but logically higher grade is cleaner fuel.

Originally Posted by Bloody Arro

It basically depends on how long you want to keep the engine. The better the grade, the better it is for the engine and the longer it will last. The difference in the quality isn't THAT great, but over time it will show.
I personally use premium unleaded because my car is part of the 200k club and I also get a little better mileage out of the higher grade.

Originally Posted by Staninator

It's highly debatable but logically higher grade is cleaner fuel. I fill up with 89 octane and it runs smooth.

Originally Posted by sl33pyriceboi

WRONG WRONG WRONG WRONG.

do not listen this BS.

a higher octane gas doesnt mean the fuel is a "cleaner fuel" nor does it mean ur engine is gonna last longer.

if this is what you think, you know absolutely NOTHING about fuels.

basically higher octane allows an engine to run high compression (if the engine was designed for that specific octane)


the 2009 LX is designed for a 87octane or equivalent. running any HIGHER octane (higher than 87) will make you LOSE miles-per-gallon and lose horsepower.....not to mention you are WASTING ur money.


anyone who argues other wise is a dumbass who needs to do a little bit of learning/reading/researching before they miss inform other people with their "logic"

Originally Posted by Staninator

i've read it all believe me... but okay...

Originally Posted by StardustLily

sl33pyriceboi: you being an *** about it is not necessary you know, and you aren't entirely correct, you are generalizing...

To the OP: if your engine is stock, then go with whatever the manual tells you to do. If it says 87 or higher, well then anything 87 or better is what you should use. If your engine is not stock, adjust fuel grade accordingly (turbo setups need higher grade, etc).

Another thing I have noticed is some premium fuels contain no ethanol, other additives, etc. It's going to boil down to where you get it from and the effects of different fuels will change depending on what engines they are used in.

As for the "losing MPG and losing horsepower", I will call BS on that. Although there is some validity in sl33pyriceboi's statement, it is VERY generalized. Reading and research etc mean absolutely nothing when set beside experimentation data and physical findings. If you REALLY want to know what sort of effects different grades of fuel have on your car, test it out. Plan a 5 hour highway drive and one way use 87, the next use 91 or something and then check where the needle is at certain points and record the data and then compare. That will tell you quite quickly if sl33pyriceboi's theory of "improper" fuel grades has any validity whatsoever for your specific car.

Not to bash you sl33pyriceboi, as your points do have some validity, but I hate generalizations...

Originally Posted by v6p.net

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What octane fuel should I be using in the J30A1?
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A mini-primer on octane, ignition timing, and air-fuel ratio tuning.

The short answer: 87 octane and nothing more. Yes, even for best performance - just 87 octane. Higher octane fuel will actually give you LESS power on the J30A1.

The long answer:The octane requirements of an engine are directly related to the compression ratio of the engine and how it's tuned (primarily ignition timing and air-fuel ratios) from the factory. Combustion chamber design also has a play. It has nothing to do with the number of cylinders (i.e., the J30A1 doesn't need premium just because it has 6 cylinders vs a 4 cylinder.)

By today's standards, the J30A1 runs a relatively low 9.4:1 CR (compression ratio) which decreases its need for octane. 10.0:1 would be considered medium, and 10.5:1 or above would be pretty high for a production general consumer market engine. Typically a 10.0:1 CR is the crossover point on whether an engine will need higher octane fuel or not. A conservatively tuned engine with a 10.0:1 CR can do fine with 87 octane, but one with more advanced tuning will need premium. Due to the J30A1's low compression ratio and also its conservative state of tune (both ignition timing and air-fuel ratio), it performs the best on 87 octane fuel. Anything more will actually DEGRADE performance, not improve it. This was proven by a chassis dyno test on a J30A1 powered Accord by Car & Driver magainze in November 2001, and also proven at the track by previous G6 Accord V6 owners - they ran a few tenths slower due to premium fuel.



Although at the peak the engine only "lost" 4 whp on higher octane fuel, that is nothing compared to the vast amount of power lost in the lower rev range. Although torque was not plotted here, the difference equates to as much as 15 lb-ft of torque lost all throughout the low-end and mid-range which is very significant and would be noticeable on the "butt dyno".

Contrary to popular belief, higher octane fuel does not have more energy per gallon than lower octane fuel - it actually has LESS. Octane is a flame retardant that actually slows down and acts to prevent combustion from happening. Therefore, the more octane in your fuel, the more difficult it is to burn. In order to compensate for this slower and more difficult burn, ignition timing would need to be advanced such that combustion would start much sooner. By the time the piston reaches TDC (Top Dead Center) the combustion process needs to already be at or near its peak such that there is a maximum amount of force available to drive the piston downward with. This ignition timing is set and tuned specifically for 87 octane fuel in the J30A1. With higher octane fuel, combustion takes place more slowly. Since there is no built-in mechanism to properly advance the ignition timing for higher performance and higher octane fuels on the J30A1, this means that with the slower burning fuel there is now LESS power from combustion to force the piston downward with by the time it reaches TDC and this reduces torque output. In addition, any combustion that is still taking place at or beyond 20-25 degrees ATDC (After Top Dead Center) does not contribute significantly to the engine's torque output and is therefore wasted. With higher octane fuel and no timing advance, more of the combustion process is likely to take place at or beyond this range and therefore not contribute to the engine's power.

This is why properly tuned ignition timing is so critical in modern engines. To much timing advance and the knocking phenomenon can occur which can destroy an engine if severe enough (oversimplifying: knocking occurs due to too much compression/timing advance for a given octane level). Too little timing advance and you're not getting the most you can out of the engine and it's not running as efficiently as it could both in terms of torque production, fuel mileage, and even emissions. Since the J30A1 engine does not have a knock sensor that can tell the computer to retard the timing in the event that knocking occurs, this forces Honda to set the default ignition timing extremely conservatively and for the lowest common denominator octane level of 87. Therefore, if you are fueling your J30A1 with anything higher than 87 octane, you are purely wasting your money. As Car & Driver's test concluded, you pay more money for higher octane fuel, but get less power with the J30A1, and that has been backed up by track testing from members here. C&D's panel of experts did not know why exactly that was with the J30A1, but we know here at V6P.

The flip side however is that the J30A1's very conservative NA (naturally aspirated) properties make it ideal for boosting (supercharger, turbo, etc), although you do still need to watchout for knocking since there is no knock sensor. Gaining all-motor performance with the J30A1 is very difficult and expensive, and will have perhaps one of the lowest horsepower gain to dollars spent ratios out of any car out there.

References:
- A search for various combinations of the words octane, ignition, timing, performance, dyno, and compression netted countless excellent technical writeups from respectable sites which I have been reading for some time now.
- OBD-II scanning logs from my Maxima while playing with the knock sensor.

Originally Posted by Bloody Arro

It basically depends on how long you want to keep the engine. The better the grade, the better it is for the engine and the longer it will last. The difference in the quality isn't THAT great, but over time it will show.
I personally use premium unleaded because my car is part of the 200k club and I also get a little better mileage out of the higher grade.