I have heard that you get slightly better economy when using higher octane fuel. I use 98RON & it seems I get a little bit more economy, but it's hard to be certain. I only use it because the car runs a hell of a lot better than when on the recommended 91RON.
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unless your car only takes premium fuel (like mineeeeee) then no, i don't see a difference. in fact with higher octane you car might not be able to burn it all off..
i don't see an improvement on my 1990 DA when i used 89 vs. 91 octane..
Mods: Go-fast stuff, Alpine 9855, Infinity Perfect 10.1 & 6.1 w/ a few hundred watts on each via Pioneer 5100T & 7100M.
Quote:
Originally Posted by Transparent
I heard you get better milage from higher octane because its got less other crap in it. but those are just rumors i picked up somewhere no proof
Stupid rumor. Your gas mileage will go down if you use higher octane. The different amounts of component chemicals that make up higher octane gas cause the gas to both detonate at a slightly higher temperature and output a slightly lower amount of stored energy.
Quote:
Originally Posted by mls
I have heard that you get slightly better economy when using higher octane fuel. I use 98RON & it seems I get a little bit more economy, but it's hard to be certain. I only use it because the runs a hell of a lot better than when on the recommended 91RON.
The only reason you would see a difference is if the ECU senses knocking on the lower octane gas and it pulls back timing, forcing you to push the gas more to get the same power (and making gas mileage suffer).
Quote:
Originally Posted by IntegraXTR
unless your car only takes premium fuel (like mineeeeee) then no, i don't see a difference. in fact with higher octane you car might not be able to burn it all off..
i don't see an improvement on my 1990 DA when i used 89 vs. 91 octane..
You will get pretty much the same percentage of unburned fuel using any octane rating.
The octane rating of your gas indicates at what compression and temperature the gas will ignite. It does not do anything for gas mileage as the octane rating will not affect the air to fuel ratio. If air to fuel ratio isn't effected, then the same amount of gas goes into each cycle.
what octane does do is, it increases output torque of your engine. The higher the octane, the higher your torque output is. Hence there is racing fuel sold at every drag strip.
Mods: Go-fast stuff, Alpine 9855, Infinity Perfect 10.1 & 6.1 w/ a few hundred watts on each via Pioneer 5100T & 7100M.
WTF?
NO.
You are stupid.
Here's why.
Quote:
Originally Posted by ryuryubu
The octane rating of your gas indicates at what compression and temperature the gas will ignite. True. It does not do anything for gas mileage No, idiot. As I have already stated, higher octane gas has a lower amount of stored energy per volumetric unit. Therefore same air/fuel, same compression, same ignition advance, same everything... and you will get less power out. as the octane rating will not affect the air to fuel ratio.This is true, but irrelevant. If air to fuel ratio isn't effected, then the same amount of gas goes into each cycle. Again, true but irrelevant
what octane does do is, it increases output torque of your engine.Here's where you really cross the line from ignorant to retarded. The higher the octane, the higher your torque output is. Um.... no. Hence there is racing fuel sold at every drag strip. Now that you are done being a rambling idiot, I will explain a little about how cars work. Going back to the first sentence of your post (the one marked 'True'), octane is a measurement of gasoline's resistance to ignition. The higher the octane, the harder it is to detonate it. If your car does not ping/knock with timing advanced to its optimal setting and a/f ratio at near 12:1, you will do nothing but LOSE power by using higher octane gas. If you have some pinging, using higher octane will allow you to set the timing and fuel to get the most power (more than you would make on the lower octane gas without the engine eating itself).
The reason the 110+ race gas is sold at tracks is that most race engines have higher dynamic compression (by milling heads, flat top pistons in place of domed, use of forced induction, or aftermarket cams), more timing advance, and often reach higher cylinder temps than the stock counterparts, and will be able to make use of the higher octane gas in a way to will greatly overcome the lower energy density (whereas a completely stock engine will not).
just use whatever the manufacturer recommends for your car (stock cars).
if you use a higher octane it doesnt necessarly mean that you gain more HP or milage from it.
in fact, some cars will lose a few HP if you a higher octane rating than what is recommended (accord v6 for example, 98-02).
in fact, some cars will lose a few HP if you a higher octane rating than what is recommended (accord v6 for example, 98-02).
yahh i seen that dyno test in car and driver
from the accord forum:
Quote:
In many high-performance situation, riders clamor for higher octane fuels, thinking this will give them additional horsepower and, thus, an advantage over the competition. But this is not the case--adding higher-octane race fuel to your motorcycle may actually produce less horsepower. Here's why: Octane, an arbitrary number which is calculated as the average of the Research Octane Number (RON) and the Motor Octane Number (MON), and is only an indic ation of a fuel's sensitivity to knock, which is typically pressure-induced self-ignition. (Of these two ratings, MON is more applicable to racing fuels as it is measured under high load and high speed conditions.)
Octane, as you can see, is not a measure of how much power--or, more correctly, specific energy--is contained in a fuel. And remember that leaded high-octane race fuels burn slower than most unleaded fuels, and may reduce performance in stock or lightly modified motorcycles. A high octane rating itself, however, does not mean that the fuel is slow burning. Hence, it has no direct bearing on the power characteristics of the fuel.
The knock tendency (and hence, the Octane rating) of a fuel is a function of the amount of free radicals present in the fuel prior to ignition and can be reduced by the addition of tetra ethyl lead, aromatics and other additives.
Although some racing organizations still use maximum octane number as the discriminating factor for fuel legality, it is really not appropriate for racing purposes.
Instead one should look at the amount of energy (heat) released in the burning of a particular fuel. This is described by the specific energy of the fuel. This quantity describes the amount of power one can obtain from the fuel much more accurately. The specific energy of the fuel is the product of the lower heating value (LHV) of the fuel and molecular weight of air (MW) divided by the air-fuel ratio (AF):
Specific Energy = LHV*MW/AF
For example, for gasoline LHV= 43 MJ/kg and AF=14.6, while for methanol LHV= 21.1MJ/kg (less "heat" than gasoline) and AF=6.46 (much richer jetting than gasoline). Using the above formula we see that methanol only has a 10% higher specific energy than g asoline! This means that the power increase obtained by running methanol, with no other changes except jetting, is only 10%. Comparing the specific energy of racing and premium pump gas you can see that there is not much, if any, difference. Only alcohol s (such as methanol or ethanol) have a slightly higher specific energy than racing or pump gas.
Other oxygen-bearing fuels, besides the alcohols and nitromethanes, such as the new ELF fuel, will also produce slightly more power once the bike is rejetted. However, at $15.00 to $20.00 at gallon for the fuel the reportedly minor (1% - 2%) improvement is hardly worth the cost for the average racer.
The real advantage of racing gasolines comes from the fact that they will tolerate higher compression ratios (due to their higher octane rating) and thus indirectly will produce more power since you can now build an engine with a higher compression rati o. Also, alcohols burn cooler than gasoline, meaning even higher compression ratios are possible with them, for even more power.
The bottom line here is that, in a given engine, a fuel that doesn't knock will produce the same power as most expensive racing gasolines.
However, it sometimes happens that when you use another fuel, the engine suddenly seems to run better. The reasons for this are indirect: First, the jetting may be more closely matched to the new fuel. Secondly, the new fuel may improve the volumetric e fficiency (that is, the "breathing") of the motor. This happens as follows: Basically a fuel that quickly evaporates upon contact with the hot cylinder wall and piston crown will create additional pressure inside the cylinder, which will reduce the amount of fresh air/fuel mix taken in. This important--but often overlooked--factor is described by the amount of heat required to vaporize the fuel, described by the 'enthalpy of vaporization' (H), or 'heat of vaporization' of the fuel.
A high value of H will improve engine breathing, but the catch is that it leads to a different operating temperature within the engine. This is most important with two-strokes, which rely on the incoming fuel/air mix to do much of the cooling--even mode rn water-cooled two-strokes rely on incoming charge to cool the piston. For two-strokes a fuel that vaporizes, drawing a maximum amount of heat from the engine, is essential--the small variations in horsepower produced by different fuels is only of second ary concern.
Also important is the flame speed: Power is maximized the faster the fuel burns because the combustion pressure rises more quickly and can do more useful work on the piston. Flame speed is typically between 35 and 50 cm/sec. This is rather low compared to the speed of sound, at which pressure waves travel, or even the average piston speed. It is important to note that the flame propagation is greatly enhanced by turbulence (as in a motor with a squish band combustion chamber).
The most amazing thing about all this is that you can get the relevant information from most racing gasoline manufacturers. Then, just look at the specification sheet to see what fuel suits you best: Hot running motors and 2-strokes should use fuels wit h a value of "H" that improves their cooling, while more power (and more heat) is obtained from fuels with a high specific energy.
By the way, pump gas has specific energies which are no better or worse than most racing gasolines. The power obtained from pump gas is therefore often identical to that of racing fuels, and the only reason to run racing fuels would be detonation probl ems, or, since racing fuels are often more consistent than pump gas--which racers call "chemical soup"--a consistent reading of the spark plugs and exhaust pipe.
summary: use what's rated for your car. anything more is just a waste to your wallet.
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The only reason you would see a difference is if the ECU senses knocking on the lower octane gas and it pulls back timing, forcing you to push the gas more to get the same power (and making gas mileage suffer).
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