MPG Questions
07-07-2010, 03:19 PM
#41
Moderator
Join Date: May 2010
Location: Where my car is.
Posts: 724
Alright, now let me get this straight... you guys all pump 89 or less octane in your ride, and you get BETTER mileage? Hmm... so let me ask- where the hell do you guys pump your gas, because you all probably found a place that has very little ethanol in their regular and mid grade gas, and that, imo, is harder to find than a rust free DA...
This is my understanding of fuel mechanics and chemistry. I may be wrong, and if I am, I'd appreciate it if someone were to point out where I've spoofed.
Theoretically, 87 octane gas is supposed to give better mileage:
- n heptane, a straight chained hydrocarbon (no branches), is found in larger quantities in 87 octane gas than in 91 octane gas (remember, a gas with straight n heptane has a 0 octane rating). Needless to say, a straight chain hydrocarbon isn't that compact- meaning that it has a lower melting and vaporization point- ideal for fuel injection engines, which must convert the gasoline into a vapor before initiating combustion. (Why vapor? well, try burning a log of wood and sawdust- the log will burn slowly, the sawdust will literally explode- its the surface area of the molecule that determines combustion. The same applies for molecules, n heptane can easily separate into a more vaporizable form, easily initiating combustion.
- 2,2,4 trimethyl pentane (isooctane), has secondary and tertiary carbons present on both ends, so due to a higher number of carbons, and a more compact structure, it has a much higher melting/vaporization point than n heptane. Thus, it is much harder for fuel injectors to vaporize isooctane for combustion- small droplets with less surface area and more fuel results per burn, yielding an incomplete burn.
So why, when I pump 87 or 89 octane, do I get less mileage? (last tank I got 12.1km/L using 91- the 89 brought it down to around 10km/L (average of 4 fill ups). I have a 91 integra RS, 1.8 L non VTEC engine, stock timing.
Its in the ethanol. Compared to n heptane and isooctane, it is hard for ethanol to vaporize. Despite ethanol being a smaller straight chained molecule, ethanol has an OH group, which enables it to form hydrogen bonds, thus drastically lowering vaporization.
So although the n heptane slightly increases vaporization and mileage of the 87 octane, the addition of 10% ethanol in the gas will lower it (unless the ethanol molecules are evenly dispersed, thus reducing the chances of the ethanol molecules in bonding with each other).
***I currently use ethanol free Shell 91 octane- I tried the ethanol laced 89 and 87 stint for a month or so, and I didn't like it. I absolutely wish that a gas station that sells ethanol free 87 gas would open up, but now with Ontario Ministry of Environment mandating a push for up to 15% ethanol in the gas... soon the ethanol free 87 of yesteryear will be harder to find than crack!***
This is my understanding of fuel mechanics and chemistry. I may be wrong, and if I am, I'd appreciate it if someone were to point out where I've spoofed.
Theoretically, 87 octane gas is supposed to give better mileage:
- n heptane, a straight chained hydrocarbon (no branches), is found in larger quantities in 87 octane gas than in 91 octane gas (remember, a gas with straight n heptane has a 0 octane rating). Needless to say, a straight chain hydrocarbon isn't that compact- meaning that it has a lower melting and vaporization point- ideal for fuel injection engines, which must convert the gasoline into a vapor before initiating combustion. (Why vapor? well, try burning a log of wood and sawdust- the log will burn slowly, the sawdust will literally explode- its the surface area of the molecule that determines combustion. The same applies for molecules, n heptane can easily separate into a more vaporizable form, easily initiating combustion.
- 2,2,4 trimethyl pentane (isooctane), has secondary and tertiary carbons present on both ends, so due to a higher number of carbons, and a more compact structure, it has a much higher melting/vaporization point than n heptane. Thus, it is much harder for fuel injectors to vaporize isooctane for combustion- small droplets with less surface area and more fuel results per burn, yielding an incomplete burn.
So why, when I pump 87 or 89 octane, do I get less mileage? (last tank I got 12.1km/L using 91- the 89 brought it down to around 10km/L (average of 4 fill ups). I have a 91 integra RS, 1.8 L non VTEC engine, stock timing.
Its in the ethanol. Compared to n heptane and isooctane, it is hard for ethanol to vaporize. Despite ethanol being a smaller straight chained molecule, ethanol has an OH group, which enables it to form hydrogen bonds, thus drastically lowering vaporization.
So although the n heptane slightly increases vaporization and mileage of the 87 octane, the addition of 10% ethanol in the gas will lower it (unless the ethanol molecules are evenly dispersed, thus reducing the chances of the ethanol molecules in bonding with each other).
***I currently use ethanol free Shell 91 octane- I tried the ethanol laced 89 and 87 stint for a month or so, and I didn't like it. I absolutely wish that a gas station that sells ethanol free 87 gas would open up, but now with Ontario Ministry of Environment mandating a push for up to 15% ethanol in the gas... soon the ethanol free 87 of yesteryear will be harder to find than crack!***
You make some very valid points. And thanks for posting this up. Was very interesting to read.
You must also take into account the compression ratio and conditions of the ignition and burning in a given engine.
As I sated before, an engine designed to properly run on 87 will not run properly on 94 and even may have issues running on 91 because it can't burn the fuel completely and efficiently.
It is possible for severe build up of carbon deposites on the piston and combustion chamber to shrink the volume of the cumbustion chamber when the piston is at TDC enough to increase the compression ratio slightly. It has been observed that this increase in compression is sometimes enough to cause detonation (pre-ignition or knocking/pinging) while using regular 87 fuel and by switching to 89 or 91, the fuels higher resistance to detonation allows the engine to burn the fuel more completely, thus better fuel mileage.
Does this mean maybe your engine has excessive build up of deposites on your piston/cumbustion chamber? I don't know. But its' a possibility that could partially explain what you are experiencing.
Also, other things like air temperature, humidity etc... will also have an effect on fuel consumption with regards to the condition of your engine and the type of fuel you use.
There are many variable factors.
07-07-2010, 04:51 PM
#42
Junior Member
Join Date: Jul 2009
Location: Scarborough
Posts: 138
You make some very valid points. And thanks for posting this up. Was very interesting to read.
You must also take into account the compression ratio and conditions of the ignition and burning in a given engine.
As I sated before, an engine designed to properly run on 87 will not run properly on 94 and even may have issues running on 91 because it can't burn the fuel completely and efficiently.
It is possible for severe build up of carbon deposites on the piston and combustion chamber to shrink the volume of the cumbustion chamber when the piston is at TDC enough to increase the compression ratio slightly. It has been observed that this increase in compression is sometimes enough to cause detonation (pre-ignition or knocking/pinging) while using regular 87 fuel and by switching to 89 or 91, the fuels higher resistance to detonation allows the engine to burn the fuel more completely, thus better fuel mileage.
Does this mean maybe your engine has excessive build up of deposites on your piston/cumbustion chamber? I don't know. But its' a possibility that could partially explain what you are experiencing.
Also, other things like air temperature, humidity etc... will also have an effect on fuel consumption with regards to the condition of your engine and the type of fuel you use.
There are many variable factors.
You must also take into account the compression ratio and conditions of the ignition and burning in a given engine.
As I sated before, an engine designed to properly run on 87 will not run properly on 94 and even may have issues running on 91 because it can't burn the fuel completely and efficiently.
It is possible for severe build up of carbon deposites on the piston and combustion chamber to shrink the volume of the cumbustion chamber when the piston is at TDC enough to increase the compression ratio slightly. It has been observed that this increase in compression is sometimes enough to cause detonation (pre-ignition or knocking/pinging) while using regular 87 fuel and by switching to 89 or 91, the fuels higher resistance to detonation allows the engine to burn the fuel more completely, thus better fuel mileage.
Does this mean maybe your engine has excessive build up of deposites on your piston/cumbustion chamber? I don't know. But its' a possibility that could partially explain what you are experiencing.
Also, other things like air temperature, humidity etc... will also have an effect on fuel consumption with regards to the condition of your engine and the type of fuel you use.
There are many variable factors.
As for carbon build up- I do admit that when I cleaned out my throttle body, I found a lot of soot- the car drove like a champ and the erratic idle was fixed- I believe this strongly suggests a lot of carbon build up in the engine...
To the OP- What exactly did you do for your tune up?
I agree with what others have said about the large 18 inch rims, but apparently the OP has just noticed a reduction in mileage and oomph after the tune up.
Hey guys, so I did a Tune up on my (auto) 2000GS.
It shifts better but i feel like it runs more sluggish and I think im getting less MPG.. I get currently 300km/ tank.. Aprox $40. I went to MTL this weekend and moth trips only got me 400km/ tank on ALL HIGHWAY.. any comments?
Now assuming that he already had his 18 inch wheels on before doing the tune up, and he didn't feel the power reduction before, the culprit must therefore not be the wheels, but something else...
07-08-2010, 02:03 PM
#43
Junior Member
Thread Starter
Join Date: May 2010
Location: Toronto
Posts: 120
thanks for all the info and support. great to read. I will try a better oil. lower grade gas. and then maybe some sort of cleaner ( seafoam or w.e ) but it may just be the wheels and the auto tranny... does anyone else here have an AUTO?? if so how many km/l do u get? or km per tank...
07-09-2010, 10:01 AM
#46
Junior Member
Thread Starter
Join Date: May 2010
Location: Toronto
Posts: 120
interesting. lol maybe since my window doesnt work the car doesnt want to run nice lol. ahhh well doesnt matter too much right now.. but if u got 350 and 450.. those are big differences.. i boot mine everywhere and get 300.. i tried driving easy to see how many k i get but its soo hard. lol
07-09-2010, 10:42 AM
#47
Junior Member
Join Date: Jul 2009
Location: Scarborough
Posts: 138
My dad gets around 450km on his 96 integra auto per fill up with 89 octane.
Last time I let my tank run on empty, I got up to 520 kms on my 91 integra auto, running 91 octane (I also use a mix of 110mL acetone and 70mL xylene for every 50L fillup, but that's besides the point...).
Now I never run my fuel tank to empty- half way and I pump (water settles in the bottom of the tank, and its really not particles and debris that gets through the fuel filter, but water).
I never tried out the seafoam (heard too many mixed opinions on that one)- but I definitely recommend throttle body cleaning.
UPDATE- after I did the TB cleaning for my dad's teg- he told me now that he's at 370km with a bit less than 1/2 a tank to go... damn he just might beat my DA's mileage :S
Last time I let my tank run on empty, I got up to 520 kms on my 91 integra auto, running 91 octane (I also use a mix of 110mL acetone and 70mL xylene for every 50L fillup, but that's besides the point...).
Now I never run my fuel tank to empty- half way and I pump (water settles in the bottom of the tank, and its really not particles and debris that gets through the fuel filter, but water).
I never tried out the seafoam (heard too many mixed opinions on that one)- but I definitely recommend throttle body cleaning.
UPDATE- after I did the TB cleaning for my dad's teg- he told me now that he's at 370km with a bit less than 1/2 a tank to go... damn he just might beat my DA's mileage :S
07-09-2010, 11:10 AM
#48
Well to give you some more ideas, I'm pretty sure my teg was running rich, it barely passed emissions (has an old *** cat.. could also be eatting fuel mileage.. ) but it was completely stock with 220xxxKM, with regular Acura 5 stars on it. So if you're getting less than my rich running teg.. there must be something up in my opinion.. I drove pretty hard on it too and still managed to get 320-350 per tank. I used only 87 octane.
07-09-2010, 12:18 PM
#50
Junior Member
Thread Starter
Join Date: May 2010
Location: Toronto
Posts: 120
haha yea but 300km/tank AT MOST.. i dunno about that 1.. i used to kill my 3.0cl vtec and only get about 50km less then driving it normal per tank... my friend was getting like 550/ tank and got to mtl on one tank when he drove.. m/t 95 ls.. mines a 2000...
07-13-2010, 04:16 PM
#57
I usually get 500 plus per tank and 600 plus doing highway driving during the school year. I have a MT and shift at around 3k-4k rpm. Before I got some of my upgrades (intake, exhaust, etc) i was getting 500 max.