Gas Octane

lots of ppl seem to forget that 2008 and before tacoma manuals stated to use 91 octane for best performances. That means that the ECU was programed for 91, and may be still programmed for it even for more recent years (2009+).

 

I use 87 in my 2010 base Tacoma 4 cyl., per the manual. No issues. I usually buy at Costco. If and when I think it is an issue, I may add a Chevron fuel cleaning additive after oil changes. The gov'mint now mandates standards on gasoline and requires cleaning additives so I don't think it is a big deal.

I've never had an issue with knocking on any modern vehicle.

Besides two motorcycles, my only other rig is a Boxster S. I put premium in that because that's what's called for. 87 in the Yamaha FJR 1300 for the same reason.

I have only had the Tacoma a month and 400 miles. Bought it because the Boxster handles like a toboggan in the snow and I needed a 4WD something.

I think most of this business is psychological. We FEEL better when we change our oil every 3000 miles instead of 5000 so we do it even though it may not be necessary. People on these lists tend to care more and want to do more than the average guy so that energy goes somewhere.

I always think of the analogy of the little kid who gets a new toy and wants to jazz it up or put his personal stamp on it and ends up making the thing ugly with his magic marker and other 'enhancements.'

It's hard to beat just giving the vehicle proper maintenance and keep track of mpg and other signs something may be awry.

 

ok so explain this...

87 octane been running since I got the truck averaging 20mpg every tank.

91 octane just added the last 2 tanks to try out your guys theories about saving or breaking even by using higher octane, and each of those tanks were 17.8mpg and 18.2 mpg wtf?!!! Driving style did not change.

 

Excellent example tending to disprove* the myth about 91 octane being 'better' or having more energy or whatever than 87.

I suspect the real factors involved in such anomalies are variables in the test procedures. Dirtier air cleaners and other engine issues may also apply. It is probably impossible for any of us with our normal driving routines to have any two tankfulls of gas be subjected to identical driving conditions.


* I say 'tending to disprove' because I am loathe to use the word 'proof' re: any anecdotal report, even if it supports my own biases.

 

you know, this is just going to keep going in hug round about circles. its kinda like the discussion about what oil is better, what spark plugs, Halo Reach v. Halo 3......

Cheveron fuel add is pretty good. I put that in my girls turbo eclipse when ever we get ready for a road trip from las cruces to albuquerque.

Has anyone thought about putting it in to MYTHBUSTERS? they did an episode with fuel addatives myths and the myths about the little magnets on the fuel line and some carb that was supposed to get like 300 miles to the gallon. they also did the myth of the tail gate being down giving better gas milage.

 

I use 87. I'm not sure I believe that the 2nd Gen V6 will gain power from higher octane. Like many have said already, higher octane burns slower. I ran 93 in my Trans Am and 91 in my G8. But thats because it called for each. Someone show me a legitimate document that states the Tacoma will benefit from premium.

In Jersey we had 94 octane up until about 4 years ago. Sunoco used to have 87, 91, 93 and 94. Now its 87, 89, 91 and 93.

 

Man, people will fight about anything.

Octane is not a substance, it's a property. An octane number rates a gasoline's ability to resist compression combustion. Period. It does not improve performance by itself; if it does anything to performance on any particular car, it's only because the DME allows more aggressive mapping because it doesn't sense detonation (the extent to which this makes any difference varies widely by car). That's it, that's all.

Octane does not "burn slower" because it is not a substance and does not implicate energy value in any way. However, some fuels achieve higher octane ratings by using ethanol (the cheapest way to raise the number). Ethanol has less energy in it than gasoline. Thus, if you burn high octane fuel from Sunoco, who use a lot of it, your mileage can suffer. If you burn high octane fuel from Shell, who don't use any in their premium (around here, anyway), it can theoretically improve. But octane does not "burn".

I liked the mileage comparison someone posted earlier, but I don't think it's going to help the debate much. The mileage differences are very marginal, much less than, say, the difference ambient temperature makes (about 10% in my case, winter vs. summer, based entirely on the DME's decision to enrich the mixture when it's cold). The study you'd have to do to quantify the mileage benefit would have to be a lot more rigorous.

Premium fuel costs 46 cents a US gallon more here than regular, but I still use it. I have my reasons, but none that I've ever found change anybody's mind on an internet forum. I have to say, you're probably not missing much if you run regular fuel, but you're also not wasting your money if you don't.

 

Creemore..,.... good post, although one minor over look..

if higher "octane" can resist compression combustion more, and you increse fuel mapping with maybe a high flow filter.... then in essence it can create more being compressed in the cylinder. also, the way it combusts is different between the ratings, and the way it combusts creates a different amount of energy being transfered into the downward motion of the piston. so if you are able to compress a slightly higher combustable into a cylinder, like say 94 once it is ignited, then the engery it releases into the piston will create more transfered energy into the motions of the other pistons..... hense more power and better fuel efficiency because you need less throttle position to get the object moving.

where is the difference .46 between reg and premium? here in NM it is about .26 around .13 between reg and middle and the same between mid and high.

I would love to find a place that has 93 here in NM.

BUT IN ALL VERY AWESOME POST MAN, VERY INFORMATIVE AND VERY KNOWLEDGE AND RESEARCHED.

 

I understand your point, but I think "allows" is probably a more accurate word than "creates". The ECU makes fuel mapping decisions based on a bunch of parameters (not all of them will take additional airflow into account). Where gasoline is concerned, the only input the ECU uses is incipient knock. The engine has knock sensors which are basically little piezo-electric microphones. In principle, the ECU wants to run the most advanced timing and leanest mixture it can get away with. It 'listens' for predetonation, and then dials these back until it doesn't hear it anymore. With premium fuel - and subject to a bunch of other parameters plus the amount of variability built into the program in the first place - it doesn't have to dial them back as much.

This, by the way, is where a lot of the gains from 'chipping' come from. The low hanging fruit for DME programmers is protection from low octane fuels, and the EPA's urban drive cycle demands. Taking those two things off the table alone will usually squeeze a few more peak horsepower out of an engine.

That price bump for premium is here in Canada

Anyway, thanks for the kind words!

 

Exactly. tried to convince my brother of this who seems to believe Octane and performance go hand in hand. Octane is the most understood thing in the car world.

I try to find gas without ethanol though. We don't have any auto or emissions inspections here in SC so there are stations that sell pure gasoline. Although I usually fill up at Costco for the 3% cash back over already lower prices.

 

I ran into the same thing last summer. We were on the way to Colorado and stopped in Tucumcari, NM for the night. Went to get gas and was about to fill up with the 86 but right as I was putting the nozzle in the filler tube I thought to myself "86... that doesn't sound right." Checked 3 stations all had 86, 88 or 89, and 90something. Last one had the 89 for cheaper than the first one had 86 so I went with that. What is New Mexico trying to pull? Every vehicle I've owned requires 87...

 

Higher octane values equate to higher ignition temperatures. Higher ignition temperatures in a combustion cycle DO equate to more power if the exhaust temperatures are nominally the same for all octane levels.

The otto cycle is based upon temperature-enthalpy and Pressure-Volume charts. If you raise the temperature and have the same exhaust temp, you have more area under this curve, and therefore more power is generated from your engine. Higher ignitian temperature equates to higher pressure. There is currently a lot of research in making fuels self ignite as does diesel to squeeze out every ounce of energy from the fuel source. This, in parts, is one of the reasons Piezo-electric fuel injectors are being developed to more precisely meter fuel and push combustion efficiency up with new direct injection style engines.

Conversely, if the exhaust temp shifts up as much as your ignition temp, you have no effective gain, just hotter exhaust gasses. This is 200 level thermodyanamics. Look up the Otto cycle and review the graphs. You can see that if you have higher pressure on the upper band, you have more area under your curve, and this is more power. The power is in the distance between the power stroke and compression stroke curves. The farther apart you make these, the more power you have to work with. Higher octane values raise that upper curve, offering the potential of more power, but this also implies you have to have the same exhaust temps nominally, which is where reality might step in and undo your gains. Higher temp ignition could mean higher temp exhaust, therefore little to no gain.

 

What a great explaination...Thanks That should clear up a lot of misconception. I am sure I am not alone in elieving "octane" was an additive...or may I was LOL

 

How Newer High Performance Cars deal with Low Octane

Most newer vehicles have knock sensors, which sense when the engine is about to knock and retard the timing to prevent knocking. Thus many drivers of newer vehicles will never hear knocking. However, if the engine control system is retarding the timing, the vehicle performance (acceleration) may drop off a little. Switching to a higher octane fuel will improve vehicle performance (acceleration). Some vehicle owners manuals now state that the vehicle will operate on regular gasoline but may give better performance on a higher octane grade of gasoline.
Take care
vbibi

 

I think the explanation is a little unclear about what makes the greater power...octane doesn't. It's the more potent charge created with higher compression, i.e., increased volume, that makes the greater power. So the higher octane doesn't raise the upper part of the curve, instead it's probably more correct to say higher compression increases volume, pushes the right side further right and additionally increase in post ignition pressure by the more potent charge raising it. That increases area under the curve and makes more power.

The higher octane mitigates the secondary effects of the higher compression, pre-ignition, by slowing down the burn of the gasoline.

Higher octane can be achieved either by refining or by additives. Modern gasolines are generally refined to a lower level and additives provide the rest. Think about it: ethanol is a great octane booster and it's in almost all modern gasolines. The high octane rating of the ethanol is an inherent property that you can utilize by blending it with the lower octane gasoline.

If anyone is interested...

http://www.faqs.org/faqs/autos/gasoline-faq/part1/

There's 4 parts in total... a bit of a read but well organized so you could jump to the part that interests you.

 

I was in Colorado last week and noticed that gas prices were around 2.85 and thought wow that is cheaper then in MI.. But then I realised it was was 85 octane.. MI is about 3ish a gal for 87. It was just an observation.

 

That's because high altitude air has less oxygen per unit volume, effectively the same as lowering compression ratio.

All else being equal, at high altitude the octane needs of a given engine are less. It's common that octane is two points or so less, at each grade, when sold at stations above 3500-4000 feet.

Also, gas price differential has far more to do with state and local gasoline taxes than anything else. They charge so much more for high-octane gas because they can.

 

Ok so being that i should be living in that state very soon whats the recommened octane for the mile high city?

 

Well...my opinion is whatever regular grade unless you're towing.

I am basing that on a test I read someone did (I'm not sure it was in TW or on ToyotaNation) with their Tacoma and Scanguage II. He filled with various grades and monitored ignition timing as he drove. He found timing was pretty well fixed at most any 'normal' engine load, regular or premium grades.

The computer will pull (retard) ignition timing if the anti-knock sensors detect preignition, more octane mitigates pre-ignition and so it has to pull it less.

But he DID find that when pulling up-grade or a heavy load at highway speed it would pull timing more with regular than with premium. That suggest premium helps when it's being pushed hard...otherwise regular is just find. It's all because of the tune Toyota has given this engine in the Tacoma. I know it's capable of a lot more 'cause they get it in Lexus' from basically the same motor.

 

i use Shell premium predicated on the fact (or myth) that they don't put ethanol in their premium grade. if i wanted corn in my engine, I'LL PUT IT THERE! don't sneak it in my gasoline

Corn is a delicious food, not a fuel additive, IMO