thinking about selling MS3.....getting "Fit"

[camrycev6]

Lower octane may not throw codes but will hurt your gas mileage and your internals. Your engine is now running hotter than it should obvisously causing some slow irreversible damage. IF you dont plan to keep the car past warranty then dont worry about it. If you do, stop doing that to your car.

Actually that is not true. I will agree it may get slightly less gas mileage (probably not even noticable)

The engine is not running hotter. Why would you think that?

Todays cars are equipped with knock sensors that limit or retard ignition timing when this happens. The full horsepower and torque potential is lost when this happens. Fuel economy suffers some... but it varies with how you drive.

If the car isn't knocking, no serious damage is being done.

 

[mazdaspeedster3]

What do you think High Octane gas does? Not to sound like a smart ass but the higher the octane the cooler the explosion. Not the oposite. High performance engines create a lot of heat. The manufacturers count on high octane gas for its cooling effect.

 

[camrycev6]

No. It takes a higher ignition point to ignite a higher octane gas. This is the reason that high octane gases don't pre-detonate at higher compression rates. This is exactly why you get better performance from high octane gases verus low ones. You can get more energy (and heat) from the detonation on higher octanes because they can be ignited at higher pressures.

Also, the computer adjusts the timing (as I said) for lower octanes. You loose some power and some gas mileage, but the engine does not run hotter. Only if the engine is doing pre-ignition (because of the lower octane) would it run hotter. If it is not, there is no reason to believe it is running hotter.

Also, since 91 octane gas contains more chemical energy than 89 octane gas it would naturally burn hotter, so could you explain the "cooler explosion."

Not trying to be an ass, but I need a scientific explanation here, because your reasoning is still not making sense.

 

[jred321]

Not buying it... That may be the case for that tank at 55mph on a long trip with a fresh oil change but rare and not the average. Still better than a MS3 will ever get!

what is this based on? experience?

 

[jred321]

cooler the explosion

oxymoron? a cool explosion?



i don't know a lot about the effects of timing retardation but i seem to remember people's EGTs normally go up when they pull timing in the tuning. can't say that i know a lot about the subject but for some reason that sticks out in my mind

 

[mazdaspeedster3]

The cooling effect on fuel is related to the heat of vaporization. The higher a fuel's heat of vaporization, the better its ability to cool the intake mixture.

You are absolutely right on with your assessment. Do you run 89 in your car?

 

[mazdaspeedster3]

oxymoron? a cool explosion?



i don't know a lot about the effects of timing retardation but i seem to remember people's EGTs normally go up when they pull timing in the tuning. can't say that i know a lot about the subject but for some reason that sticks out in my mind

Different fuels burn at different temps...

 

[camrycev6]

The cooling effect on fuel is related to the heat of vaporization. The higher a fuel's heat of vaporization, the better its ability to cool the intake mixture.
?

Right. I agree with this. But do we have any data to show that 89 verus 91 to actually show a temp difference? Even better, one that matters?

 

[mazdaspeedster3]

what is this based on? experience?

Best freinds wife. Drives 60 miles one way to work a day and bough a fit a year ago hoping for those numbers, hasnt come close.

 

[mazdaspeedster3]

Right. I agree with this. But do we have any data to show that 89 verus 91 to actually show a temp difference? Even better, one that matters?

I will do my best to come up with those numbers if any. I concede if not as being educated on this thread... (wedge)

 

[jred321]

me? i run 87 in my POS


the only time i've heard cooling and fuel mentioned in the same sentence is in direct injection vs normal injection where the fuel acts as a cooling agent. never heard it mentioned in octane rating discussions. octane discussions always result in higher octane = more resistance to detonation/preignition, aka stands up to harsher conditions before lighting on fire as needed in high performance engines. i've never heard anything about the temperature at which it burns

 

[camrycev6]

I can tell you that modern engines computers regulate the pressure, the A/F mix and the timing, and therefore have incredible control on reaction in the cylinders. Old engines, two strokes, etc., don't have this ability. That is why octane rating is much more important on older cars and on cars that are unable to adjust these parameters. (Or high performance race car tuned for a specific fuel that have no need or ability to adjust.)

 

[Tom03es]

Either way, you're not running the specified gas in your car to save $.10/gallon? At least, that's the price differential around here. So you're saving yourself about $1.20 per tank by not running the correct fuel and giving up potential power and mileage because of it?

 

[coololddude]

back to the topic--sell the MS3 and get the fit. the decision is emotional and you probably have made up your mind already. i know people that are trading in 2007 BMW'S and paying $5,000 over sticker for a Prius. only after they do it will they know if it was the right decision for them. it doesn't matter that i think they should be given a one way ticket to the funny farm!!

 

[camrycev6]

Either way, you're not running the specified gas in your car to save $.10/gallon? At least, that's the price differential around here. So you're saving yourself about $1.20 per tank by not running the correct fuel and giving up potential power and mileage because of it?

I agree you aren't running at peak power or peak fuel economy. Never had a problem with that.

However, where I live, the diff. between 89 and 93 is frequently $0.20 or more. That adds up pretty quickly. However, to be honest, I just wanted to see how the car would run. Call it scientific curiousity. I will report my mileage numbers when the tank is gone.

 

[mazdaspeedster3]

So you are running a lower octane? Isnt it known your ECU takes a tank to adjust? Heard, rumor, not a fact to my knowldge, but wouldnt you get a better reading to run two tanks of 87 or 89? I want to know now. In my reading I found one statement that current ECU's can manage a 7 point octane variance, not much more. So you should be clear of detination (knock) problems with the lower octane.
The CX7 came out asking for high octane, it is now only suggested.

 

[camrycev6]

I will run two tanks of 89 and report my findings then! I figured one tank wouldn't be enough anyway because it could be a fluke.

 

[Minus]

okay, i know this isn't going to help you much but i just bought a 2003 toyota 4runner limited for 16ish and it gets 22 on the interstate and 19 in town... both i have determined personally not to mention it was its suggested mileage by toyota.

its no 30 miles per gallon, but i surely have way more room in this thing than any of my cars.