I hate to say it but avoid the ethanol blend gas as well, it doesnt burn as well and decreases the mileage. it has in mine anyway. between using e10 and 100% gasoline for me was around 15 miles more I got out of the total gasoline.

 

Alcahol has a lower calorific value by volume than petrol, which is why racing cars using methanol typically use about twice as much fuel as a more or less equivalent car running petrol (gasoline). You don't get more power out of alcohol fuels because they are alcohol, but because alcoholhas avery high octane rating so you can run much higher compression ratios using it, and it's this that typically gives better power with alcohol than petrol. If you just rejetted a petrol motor to run on alcohol (to flow about twice as much fuel) without also raising the compression (a lot) then you'd make less power.

When you dilute the petrol with ethanol you're lowering the calorific value of the fuel, meaning it produces less power for X volume consumed. This also has implications forfuel consumption.Because you have lesser calorific value in the fuelyou are probably using a wider throttle opening to make X power, and injecting more fuel to do it.

This may be an over-simplification, but that's my basic understanding (i.e. my understanding of this is very basic!). I only use alcohol blend fuel if I have no alternative at the time.

 

JohnL, Are you a chemist?

Cheggie,
I have not noticed anyone mention this: When was the last time you changed the distributor cap & rotor? Let us know if you get any results out of changing the plugs as well. I agree with the above suggested factors (tires & winter blend fuel)that could decrease the fuel economy.If I were you, I would change in Honda Manual Trans fluid or Redline manual trans fluid.(When I change my MTF I am going to use Redline since RTexasF has spoken highly of it.) You could try an oil change with something like Royal Purple oil. It's more expensive but itreally is supposed to be the best oil.
If I were you, I would perform the "general maintenance" that could still be done and see if it helps. If not, I would start checking compression and remove the tbelt cover and check things out as TexasHonda said. (unless of course, you can check compressions easier than I can - if so, go for it now)

 

with that very cool chemistry lesson from JohnL heres another question. How do the engines that are able to run E85 are also able to run regular 87 gas?

 

Not at all, so you should treat my comments on alcohol fuels with the same respect you'd reserve for any other anonymous internet 'expert'...

As I said, my understanding of this is "very basic", and may not be 100% accurate, just what I've picked up in my travels.

 

One other thing that I will mention just because some of the older honda's had odo issues. Check and make sure that your trip counter is counting the same as your odometer. Also, are your new tires the EXACT same size (diameter and all) as your old ones?

 

I'm not sure I entirely understand the thrust of your question, but here goes:

I don't know what octane your particular 'E85' brew is, but I assume it is an 85% petrol / 25% alcohol mix. Alcohol is used an an octane booster (as well as a fuel 'extender'),displacing at least some volume of the light 'aromatic' hydrocarbons that would otherwise be used in significant amount to boost the fuel's octane. These 'aromatics' include suchsubstances astoluene, benzene, xylene and possibly a bunch of other zenes, all very toxic and absorbed through the skin and from breathing the fumes! (this is serious, don't underestimate how toxic fuel is, espcially modern unleaded fuel because it typically contains a lot more of this stuff than the old leaded fuel).

Because alcohol has such a high octane (and that the alcohol won't be the only octane booster in the mix), you could make an 85% petrol / 25% alcohol blended fuel in just about any octane rating you wanted to, and what engine you could use it in would depend mostly on what the octane rating of the fuel is and the compression ratio of the engine.

"87 gas" sounds like a 'straight' petrol withan octane of 87, which is very low. To use this you'd need a low compression ratio (probably less than about 9/1), or possibly a very retarded ignition timing (still might ping though if compression is too high), or a Wankel rotary (which can run fine on almost anything, very forgiving of low octane due to the combustion chamber shape having a large surface area to volume ratio that tends to cool the air / fuel mix so much that it's almost impossible for detonation to occur, which is also the reason why rotaries tend to be dirty and not very economical, i.e. a lot of unburned fuel due to 'quenching' caused by the cooling affect on the air / fuel mix of the large surface area of the combustion chamber).

You could possibly use an 87 octane fuel in a higher compression engine, but only if the ignition timing were very retarded or the engine is fitted with a knock sensor and thus enable the ECU to retard the ignition if 'knock' (detonation) occurs. However, performance would drop way off because of the retarded timing or the ECUdetecting detonation and retarding the ignition timing until it stopped (or bumps up against the limit of just how far it actually can retard the timing). This retarding might stop the worst affects of detonation to the point that it's no longer audible or causing any real harm, but might only be able to alleviate it rather than eliminate it altogether.

Detonation is not pre-ignition (which is caused by hot spots in the combustion chamber), detonation is caused by a spontaneous ignition of fuel in some part of the combustion chamber caused by heat caused by pressure rise (compression) that is too high for the octane of the fuel to cope with (octane being a measure of the fuel's ability to resist self ignition as temperature rises). When this happens a 'flame front' from the source of the detonation travels across the combustion chamber and is likely to then violently 'collide' with the flame front caused by the ignition spark at the plug.

The two flame fronts impact each other and then create an exponentially high and almost instantantaneous pressure rise that then causes just about all the still unburned fuel to explode (rather than just burn quickly). Retarding the igniton timing may reduce this problem by allowing more time for the prematurely ignited fuel to burn before the spark fires, meaning the collision of the two flame fronts may be avoided or at least lessened in severity. But, even with a good knock sensor etc the problem may still exist so the only safe solution to this problem is to use a higher octane fuel that won't prematurely ignite from the high compression.

When detonation occurs the engine is effectively running like a diesel engine, but even if the violent collision of two flame fronts can be avoided by seriously retarding the spark, the 'ignition timing' (prematurely caused by excessive compression) will be way wrong and you might still get fairly violent percussions when therising piston prematurely encounters a rapidly rising pressure front as it's still on the way up the bore (a word I hope doesn't describe me as the author of this stream of consciousness!). At any rate, the lesson here is don't use fuel that has too low an octane rating for your engine, even if you have a knock sensor it might not be able to really cure the problem, and the engine can be seriously damaged in short order, even though you may get away with it more often than not...

Damage from detonation can include; hammered big end bearings, overheated rings and ring lands, blown head gasket, fractures in the piston, holes in the piston crown, and probably other things too.

 

00 AV6 sedan

i haven't changed a thing with my 'routine' and maintain my machinemeticulously, the temp is 20F and i warm up my car 10-15 minutes every morning. i drive about 80mph-90mph on average for 15 miles with heavy accelerationand stop and go another 5 miles with moderate acceleration.
in summer with no warm up(1 minute warm up) i got 22mpg, 27mpg if i drive sainly. then winter hit - 18-19mpg. i put BG 44k in the gas tank - 22.5mpg.
if i drive sainly - 27mpg.

consider some bg 44k or bg cf5. very good stuff. i drop a bottle in every 4,000 to 5,000 miles.

 

ok I know how the whole internal combustion thing works with diff octane levels. here in the US E85 is 85% ethanol and 15% gasoline with a 110 octane rating. so thats why I was curious as to how the flexfuel vehicles can run both given the drastic difference in octane levels.

 

I meant 85% petrol and 15% alcohol, not 25%. Just too tired to do basic arithmetic!

Still don't like the idea of using a petrol / alcohol blend in cars calibrated for a straight petrol brew, even if the octane is very good. 110 is a mighty octane rating, but do you reallly need it that high? To actuallyrequire such a high octane you'd have a very high compression (over about 11/1 or so) or pretty high boost. As a generalisation that will tend to hold true for pump fuels and probably most lesss exotic'race' brews, the higher the octane the lower the calorific value of the fuel, so less BTUs per unit of fluid volume.

This means that the higher the octane the less 'power' you'll get out of it in an engine that doesn't actually require the higher octane rating. If you do require the higher octane due to high compression (or boost, which is essentially the same thing as far as 'knock' is concerned) then you'll get more power, but not because of the fuel but rather because of the improved efficiency of the higher compression that the fuel permits you to use. You could run 110 octane fuel in almost any petrol engine, but it's only an advantage if the engine requires it, and a disadvantage if it doesn't, i.e. if you run 110 in an engine that only requires say 87, then you're wasting your money and using a fuel that is actually a worse fuel in that application.

This isn't even considering that alcohol fuel has about half the calorific value of petrol, so if you dilute the fuel with 15% acohol you are reducing the calorific value of the fuel by about 7.5%, which would really require remapping of the fuel injection to inject a richer mixture. Having said this, it's probably an over simplification because the alcohol will displace other ocatane boosters.

Rather than more or less rewriting something I've already written, below I've pasted something I wrote (unedited) on another forum that might be of interest:

Before I start, I'm no expert on the following, it's just my current understanding from what I've read:

Because alcohol has a lower calorific value than petrol has, i.e. less BTUs by volume. This means that to get the same amount of power out of alcohol (methanol or ethanol) you need to inject about twice as much of it, but even so in an otherwise unmodified engine you're unlikely to get the same power from it as you will with petrol.

(Racing engines running methanol will typically produce a bit more power than an equivalent engine running petrol, but not directly because of the fuel being alcohol, rather because alcohol fuel allows the use of very much higher compression ratios because it has such a high octane rating, and it's this that gives more power, but at the expense of using about twice as much alcohol as the equivalent petrol engine will use petrol)

Alcohol has approximately half the calorific value of petrol, so if you dilute (adulterate?) the fuel with 10% alcohol you will in theory have about 5% less BTUs in the petrol / alcohol blend than in a non alcohol / petrol blend (all petrol based fuels are blends of some description). From a power perspective this might be OK if your ECU knew what was in the tank and knew to inject a richer mixture to make up for it, but it doesn't (even if it did, it would have issues for economy). There will be real issues for economy too because if the engine is producing X% less power at Y throttle opening, you'll end up using Y+ throttle to make up for the deficit. Car fuel injection systems (and carburettors) are calibrated to run on 'petrol', not a hybrid petrol / alcohol blend with a significantly different chemical make up and an inferior calorific value.

This may be somewhat simplistic, because the alcohol is an octane booster and will mean that some of the aromatic hydrocarbons (the zenes et al) normally used as octane enhancers will still be present but in lesser quantity, and there may actually be more actual 'petrol' (i.e. heavier hydrocarbons) in the blend also displacing some of the aromatics. The light aromatics also have a lesser calorific value than the heavier hydrocarbons that make up the actual 'petrol' content of the blend (one reason why lower octane fuel will typically produce more power in low compression engines than higher octane fuel does), but not so low as alcohol. This might mean the 5% figure I stated above could be pessimistic, i.e. it may not be quite that bad.

All this talk of special home brews etc, just use 'premium' high octane pump fuel with no alcohol, don't think you can do better than the highly trained proffessional chemists at the refineries.