Originally Posted by gearbox (Post 4438227)

the facts are using higher octane gas on a regular low compression motor will result in worse performance, simply because the engine cannot properly burn all the fuel. it will also cause the main computer to mess with the timing and it will make things even worse and most likely reduce gas mileage. ive even heard of injectors clogging up from using hi octane fuel. now if you have a hi performance/compression motor, then yes you need to be using higher octane. the engine will make more power, and using lower octane fuels can actually cause engine damage.

all civics use 87 octane (altho 86 would be best), except the civic SI with higher hp motor, which uses 89 or better.

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.

http://home.comcast.net/~stevtecv6/A...s/AV6_Fuel.jpg

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 MartinL (Post 4503911)

sl33pyriceboi that is a very good post. Could my civics engine be tuned to run more efficiently on 94? When would engine knock occur then? Thanks it's always good to learn from someone informed

Originally Posted by MartinL (Post 4503909)

Hahah wow. What is it?
After I get the bolt off should clean them with a brush and spray them with the PB Blaster and then re insert? Or if they are clean just leave them be? Thanks!

Originally Posted by MindBomber (Post 4503918)

I'd go grab new bolts, usually the auto-parts store won't even charge you for a couple small bolts. You could just re-use the old bolts and spraying them down is a good idea, but if you spray them down be careful not to over torque them and snap the bolt.

Originally Posted by MindBomber (Post 4503921)

I always chuckle a bit when people use 94 octane, you should always go to Chevron or Shell since they have legit cleaning agents though. If you really want to maintain an engine well using synthetic oil is a much better place to put your money. OP if your not using synthetic oil, don't convert now it might actually hurt the engine.

Originally Posted by MindBomber (Post 4503921)

I always chuckle a bit when people use 94 octane, you should always go to Chevron or Shell since they have legit cleaning agents though. If you really want to maintain an engine well using synthetic oil is a much better place to put your money. OP if your not using synthetic oil, don't convert now it might actually hurt the engine.

Originally Posted by sl33pyriceboi (Post 4503923)

i find it strange that ur manual says 91. maybe u miss read it and maybe the manual was referring to your year as "91" ??? *shrugs*

but, according to the gov database, u use regular (which is 87)

http://www.fueleconomy.gov/feg/noframes/7617.shtml

Originally Posted by sl33pyriceboi (Post 4503927)

ahh!.... i must.....resist.... talking about....... real synthetics. lol :lol:

maybe ill do a WHOLE thread and teach u guys a lil about oils. lol but after finals tho.

Originally Posted by MartinL (Post 4504007)

What's group 3 and 4 oils?

Yeah I am going to get that PB blaster after I take my girlfriend to work. I thought I might've been turning the wrenches wrong way but then looked at the threads on the new filter so it's just really tight. (insert joke)

Originally Posted by MartinL (Post 4504007)

Yeah I am going to get that PB blaster...

Originally Posted by sl33pyriceboi (Post 4504014)

heres a quick rundown [i should be studying for my finals that is in 3hrs. haha]


oils are grouped in to different categories. the "group" refers to the base oil in a particular group.

group III oils are dino, but they are ULTRA refined (our technology of refinement can now refine dino oils to 99.99 PURE)

group IV oils are called PAO. these oils are TRULY full synthetic. meaning each oil molecule was man-made and therefore, in X amount of volume, EVERY molecule is the same. it is also very expensive to produce.

group IV oils usually cost around $15 a quart (yes...quart... not the 4$ mobil1 u find)

note: in the US, regulations allow group III to be labled as "full synthetic." (and if u have half a brain, u will realize that this is a false claim)
why do they do that? some factors are: will sell more. close enough to synthetic...etc

in europe, however, they do not allow group III to be labled as "full synthetic." only group IV are allowed to be labled "full synthetic"


the only know oils tat are group IV PAOs (on the top of my head) are: motul 300V 10w-40 and amsoil 10w-40.

that means mobil1, castrol edge....etc are not legitimately confirmed that its a true group IV oil. most likely, they are a combination of group III + IV