I've noticed some good and bad things about the hatch...What I DO like is the compartment storage area underneath the floor. THAT is useful. I've got my booster cables, spare oil bottles, wrench, etc. all stored there, and it doesn't get in the way. Kudos to Mazda on that one. It's very well thought out.
But I don't like the hatch cover.. IMO, it is bad, especially when I tried leaning over to get something deep in the trunk, and got my eyelid scratched on the cover?!? The edge is TOO sharp.
Not only that, It took me only 1 day after purchase when I realized, I was not getting the trunk space I needed (strollers, large bags, etc). It would be cool if there was some convenient place IN the car, where I could quickly store it, but there isn't. So now it's sitting in my basement! What a useless device.
Did anyone who bought the hatchback actually keep the hatch cover in place?
Thanks, "ohsoribby" and "outohound1". Now I understand. Unfortunatley, the dealer who said they had a factory rack also didn't have any literature, so I don't have a viewbook. I'm losing confidance in them real quick. I think I need to try a different dealership.
Well, the good news is that someone's aftermarket rack will fit the car. Now, I just need to do a little investigative work to figure whose it is, since Thule and Yakima aren't claiming it.
We usually keep it in our garage. We keep a plastic storage crate (w/ cover) in the back for small items and anything we'd like to hide from prying eyes.
If my wife wants to go shopping in her P5 (for anything that might tempt thieves and isn't bulky), she takes the cover with her.
I have always had rear mount racks. i'll bet rhode gear makes one that will fit on back of hatch. Less expensive and no wind noise. Might be something to consider.
I was also disappointed with the hatch cover. It looks good up and we generally just keep small stuff back there and the wife is very keen on hiding our stuff from prying eyes but when we do have to drop the seats for something big it's a pain. You have to think in advance and yank the cover out of there before you leave.
It wouldn't have been as sturdy but I would have preferred one of those roll-up covers like I've seen in some SUV's. Just roll it into a tube and push the seats forward. Then there's the back-seat headrests.......
I've got just over 1000kms on my 3 Hatch and I can already see wear in the outside of the tires. "Nibs" are rubbed out as well. And I'm not all that "spirited" a driver. Especially in Januaruy. This could get costly.
Has anyone gotten the casette player and/or the auto dimming mirror with compass and temperature? How much do these parts and installation typically cost?
MPG5, thanks, but that won't work for me. One of the main things I carry on the roof is between 1 and 3 kayaks, at least 30-40 times per year. Sometimes, I'll carry skis, and occassionally, my daughter will want to carry a surfboard. Rarely (1-2 times per year) I'll carry a canoe. Not infrequently, I'll also need the extra room up top for camping gear.
Mazdastuff.com or Trussvillemazda.com sell these items for discounted prices. Expect to pay about $172 for the cassette and $194 for the mirror. The cassette is a breeze to install if you are at all mechanically adept. It should take no more than 15-20 minutes. Many dealers will install this gratis if you buy the part from them. The mirror is a bit of a pain due to wiring. Expect it to take up to 3 hours of a service technician's time. Service rates in my area run about $80/hr. So ~$240 for installation on the mirror.
Thanks boggse. I called a few dealers for prices and yes as you said the mirror turns out to be too damn expensive for the part and installation. Too bad I have to forget about it ( One dealer estimated $112 for installing the cassette player. From what you are saying, it should be very eaasy to install - do you think we can do it ourselves?
The manual recommends a 87 or above octane rating. Is there any benefit to using 89/91 or will that be just a waste of money with absolutely no benefit?
Each engine is a little different, but it is safe to say there should be no benefit to using greater than 87 octane on the 2.0L FS engine. That said, some brands of fuel contain better detergents and other additives. Chevron is often considered to have the best additive, called Techron. With a few exceptions like HESS, the fuel itself in a given region all comes through the same distribution center. The additives are added at the fueling station, so different brands of fuel do have significantly different products.
If the engine is designed for 87 it will work most efficiently with that grade. Using a higher grade could actually cause problems such as carbon build-up. In any case it's a waste of money unless the engine is set up to use it.
I'm not sure higher octane is always bad. I ran a '83 Prelude on 92 for 100,000 miles and the exhaust and muffler were still pristine, while others I knew were replacing them at 50-60K...
In modern engines, using fuel with an octane rating that is significantly higher will cause carbon build up in the emissions control system. 89 would probably be OK, but it wouldn't gain you anything in performance or engine life, so what is the point?
Not to question the "lower-octane is better" folks, but how does higher octane lead to carbon build up?
The job of fuel components which define "octane" , simply put, is to stop premature piston firing. Higher performance engines run hotter, so they need a higher octane to stop the pistons firing before they should. This is the most simplistic, yet the most accurate way of putting it (exceptions aside of course).
Now for engines that aren't so high powered...say a 1.7L Honda Civic, they are fine to run on Octane Grade 87. You can run them on Octane 91, or even Octane 94. Will it make a difference? No. But it should not harm the engine, so far as I know. If this is not the case, please enlighten.
Now, the only case I've heard of where one should run Octane 89 or 91 on a car that says it can get by on Octane 87 are those advanced higher performance engines with octane sensors. In these cases (I think Acura has 1 or 2 models like this), the motor runs better on Octane 89/91 because it wants to run hotter, but if it detects Octane 87, it will downgrade performance to keep the engine cooler, so that the engine won't knock.
Oh, there is one more more situation: - if you are going on a long road trip where there are lots of hill, and your vehicle is loaded to max towing capacity, then I've heard it's a good idea to upgrade to Octane 89 in case one's engine gets too hot (combatting those hills).
Other than that, upgrading to a higher octane is a waste of money. Some "premium" fuels have more cleaning additives/ethanol/etc which can be somewhat beneficial to run continuously 2 weeks before an emissions test, but the higher octane they provide generally speaking do nothing in and of themselves for most cars that are Rated to run 87.
Higher compression can also be a factor in need for higher octane. I just don't see how using higher octane can lead to carbon build-up in an engine (rated for lower octane).
Waste of money? Most of time. Harmful? No way..
But if someone has info to the contrary, please reply.
Higher octane fuels burn slower, so a larger percentage of the hydrocarbons will not be burned during the combustion cycle compared to a lower octane fuel. These unburned hydrocarbons are the source of the carbon build up. This assumes that the higher octane rated fuel achieves its octane rating through a larger percentage of long chain (over simplifying a bit here) hydrocarbons and not through the use of anti-knock additives like tetra ethyl lead (leaded gasoline).
Sorry Ted, but the combustion is very fast. In average, the flame front is propagated at the speed of 15-30 m/s. The speed might vary a little with respect to the octane index, but negligible. The whole combustion takes about 2 milisecond. At 6000 rpm, the time for the piston go down from top to bottom is: (60 / 6000 / 2) sec = 50 milisecond. 50 milisecond is largely bigger than 2 milisecond. Hence, if the fuel/air mixture is correctly balanced (O2 sensor supposes to take care of that) then there is no remaining unburned hydrocarbon, whereas it's 87 or 92 gasoline.
There is a delicate balance between maximum efficiency and detonation (evidenced by pinging). Unless the computer can adjust for the higher octane using the feedback from the O2 sensor, I believe using 91 in an engine designed and tuned for 87 will result in extra unburned hydrocarbons. Whether or not this is significant, and whether or not it results in carbon build-up and/or higher emissions is a good question. Take the 2000-2003 Nissan Maxima for example. While Nissan recommended premium (91 octane) for this car, it ran fine on 87 (I saw plenty of these in rental fleets and I know they weren't putting 91 in them), as it knew how to adjust for the fuel being used. The question is, does the Mazda3 (and other cars designed for 87 octane) know how to adjust for the HIGHER octane? Regardless of the real answer to that question, the question I would have is, why spend the extra money for nothing?
In order to take advantage of the high octane gas, one needs two things in the design:
1) high compression ratio 2) "aggressive" (i.e., early) spark-plug timing.
Such design can still use lower octane gas, by adjusting the spark-plug timing, thanks to the anti-knock sensor.
Mazda3 Australia-spec can do this (but the engine efficiency is crappy when using regular gas).
The way I understand it, N/A Mazda3 engines is tuned for regular gas. It doesn't have both characteristic 1) and 2). So, no, it can't take advantage of higher octane gas. But when runing with regular gas, N/A-spec Mazda3 is more efficient than AU-spec Mazda3.
I wonder what they do for the South American and Mexican markets where fuel can be of questionable quality? Hmmm, do they even sell the Mazda3 in Mexico?
Mazda3 are sold with 1.5 and 1.6 engines for the rest of the world. It has drum rear brake or something like that. I don't know when it will be launched in Mexico.
When I was visiting Colombie 2 years ago, I got to drive a P5 with 1.4L engine and drum rear brake!
I got curious so checked the S.A. web sites. Looks like only Puerto Rico has the Mazda3, and they seem to be getting about the same engines we get in the US (2.0 Litros o 2.3 Litros, con 148 o 160 caballos de fuerzo)!
Some S.A. countries still sell the 323 and 626!
Couldn't find a web site for Mexico at all. They make the engines but don't sell the cars there?
There are always unburned hydrocarbons. I invite you to visit an autocross and sample the unburned gas coming out of the tailpipes. EGR valves are supposed to reduce the amount of unburned fuel that is emitted by passing exhaust gas back into the combustion chamber, but when engines are pushed hard, large amounts will pass through. Unburned hydrocarbons are the source of smog. This is one reason fuel economy suffers if you drive your car like Michael Schumacher all the time.
Even though the flame front can ignite the whole volume of the cylinder in the time it takes for 60° of crankshaft rotation, it isn't necessarily a complete burn. Since premium burns slower, an incomplete burn will produce more unburned material than regular in an engine designed for regular.
I don't think it's accurate to say Higher Octane fuels "burn slower". They certainly don't prematurely ignite at lower temperatures as easily (that's the point). But when the spark plug provides the ignition source, combined with the enormous compression pressures, Octane 91 gas will burn up just as easily as Octane87. There really should be no excess carbon buildup for Octane 91 over and above what you'd see for Octane87. Naturally, there will be excess hydrocarbons produced, but that would happen in any event. Ted, I think your concerns relate more to alternative fuels which may not work at the compressions pressures, temperatures, and spark level seen in gasoline engines.
Here is what a professor at the University of Missouri says (keep in mind he's talking about "hard" drivers): and here's the link: http://www.missouri.edu/~news/archives/tipsarchive/july00tip.html -------------------------------------- Paying Higher Prices for Premium Gas at the Pump May be Worth It
With gas prices today as high as they are, people are looking to cut corners to save at the pump. While choosing a lower grade of fuel might help to reduce costs in the short run, a University of Missouri-Columbia professor says that it sacrifices engine performance and could have adverse effects on the life of the engine.
Premature ignition in the engine, also known as knocking, occurs when the engine isn't running properly. The way to minimize this problem is to raise the octane level of the gasoline, said Bob Tzou, an MU professor of mechanical engineering. Octane helps the engine resist premature ignition. The higher the octane level in the gas, the better.
Contaminants in the engine often result from premature ignition, leading to an increase in chemical residues. Over time, this incomplete combustion can have adverse effects on the life and performance of the engine, costing a car owner much more in repairs.
Tzou suggests these five tips when filling up your car:
Always use the highest possible octane gas if price is not a major concern. This is particularly the case if you want to keep your car for a long time.
Fuel your tanks by high-octane gas if the engine is working hard. Heavy-load towing, long-distance driving and hot summer days are typical examples.
An older engine may be more sensitive to the octane number than a new engine. Upgrade the octane number to the next level (for example, from 87 to 89 or from 89 to 91) if you find the car that you have driven since new starts to knock on the road. This usually happens in hard-working conditions described above.
High-octane gas always should be used by aggressive drivers who love the thrill of acceleration. The price for the thrill increases as the price of premium gas increases.
If you have been using 87-octane gas and knocking has not happened, use a no-lead fuel injector (carburetor) and engine cleaner to prevent chemical buildups, due to possible premature ignition. This is particularly important if the engine is old. This product is available in supermarkets and many gas stations. - Ben Kampelman ---------------------------------------------
I live at 5000 feet altitude, and regular is 86 octane instead of 87. I believe this is done to maintain low emissions with less oxygen available. To me, this 1 point octane difference demonstrates the delicacy of the balance between performance, efficiency, and emissions.
I live at 5000 feet altitude, and regular is 86 octane instead of 87.
You know why? This is classic. Because gas companies want to save $$$, that's all.
On high altitude, for the same car, the octane requirement is less. Here is few factors that require higher octane:
- high pressure -> low altitude, turbo engine, compressor, high compression ratio. - high temperature -> summer - high engine load -> going uphill, lug the engine
That guy is talking about using higher octane when the engine is exhibiting knocking or pinging(prematurely ignition), hard driving, heavy loads, or is old. In those cases I would agree with the recommendation to go up in octane. In other words, there is some reason why the ehgine needs a higher octane fuel. But, the Mazda3 is a new car and US/CA models aren't designed to adjust for higher octane, so unless you're pulling a boat or autocrossing I would say his recommendation doesn't apply to this car.
I believe you that they are saving money, but if it caused pinging here (it doesn't) they wouldn't be able to get away with it, right?
I drove to the top of Pikes Peak once (14,110ft). Yeah, the car got real slow at the top. Incidently, the US military tested early aircraft turbos up there.
Q: What octane would be required at 20000ft? A: It doesn't matter as the car probably wouldn't run anyway.
Octane numbers on different kinds of gas represent their ability to resist premature ignition (due primarily to pressure - not heat). Some condition may occur where (although it should not be so) the octane level of an 87 gas may in fact end up being one or two numbers lower due to other variables. In this very rare case, the engine will knock - not a good thing. We're talking one in a million chance here though.
There is no performance enhancement that correlates to octane number - it only refers to its ability to resist knocking.
Some auto manufacturers (especially Nissan) are running a very nice scam. They engineer their cars to run best on 91 octane fuel. Most manufacturers would just smack on a label telling the owner to use only unleaded premium (91 or higher) gas. No, they don't do that. To qualify their cars as 'regular gas' consumers, they equip their cars with knock sensors to avoid premature ignition and compensate by firing the spark plugs earlier and reducing engine performance at the same time if the user uses fuel with a lower octane number - even 87. Why do they do this? So they can advertise their cars as using 87 octane gas for penny pinchers. All the while, their cars will run best on 91 or higher octane fuels.
Now, most manufacturers now equip their cars with similar knock prevention devices, but these are meant to save the engine in the case of low octane fuel being used by accident. There is no reverse system that enhances performance by using fuel with a higher octane number.
The Mazda3 and most cars that simply request 87 octane will run best with that fuel and any higher octane is just money out the window. If you want to make damn sure that you never drop below 87 by some rare fluke, sure use 89 as an insurance policy - but don't expect any perfomance increase or longevity issues with that.
The gas companies are promoting high octane as high performance. It's a sales pitch. This is just not true. Sure some high-performance (read as high-compression) engines need high octane, but this is for knock resistance, not added performance.
Flame speed is generally not an important parameter for engine operation, as long as the flame can reach the boundaries of the cylinder during the proper part of the cycle.
And as my simple calculation above shows, there is plenty of time for the flame to reach the entire cylinder.
I agree that there is no need to run the Mazda3 on higher octane. In fact, I've said quite a few times that it's probably a waste of money It's just that I don't think the higher Octane of 89 or 91 will HURT the engine in terms of carbon buildup. In effect, for the Mazda3 engine, Octane 87 through 91 should make NO difference (positive or negative).
(unless one REALLY drives the car hard up hills all the time with the vehicle fully loaded with payload).
Do you have to be a Canadian to get them.I'm sick of paying .$20 more a gallon for 91 to 93 octane. I have a RSX type S and was thinkig of getting the Maxda Hatch. Will I be Disappointed (Torque )?Iv'e priced them out also and it comes close to 20K. Please enlighten me.
Since higher octane fuels have an implied higher percentage of longer chain hydrocarbons, that means more energy per molecule due to a larger number of carbon-carbon and hydrogen bonds. That means it can and will burn slower and still exhibit a flame speed almost identical to lower octane fuels. I have seen numerous discussions around the net where this has been discussed before. There is always disagreement about whether premium fuel burns slower than regular. From what I know of chemistry, the rate of combustion for 2 mixtures with different ratios of the same constituents should not be the same. Feel free to disagree.
Are there enough unburned hydrocarbons generated in a single crankshaft rotation to cause carbon buildup? No.
At an average engine speed of 3000 RPMs over the course of the first few years a motor is in service, will premium fuel in an engine not designed for it cause carbon buildup from an excess of unburned hydrocarbons? It could. More so if you keep the engine higher in the rev range.
This is all my opinion which is based on my understanding of chemistry (5 semesters in college including Organic and Geochemistry plus a Chemist wife) and what I have seen in the last few years from people using premium in cars that do not need it, thinking they are getting more power from it. Why do you think repair shops sell so many engine cleaning services? It is an unnecessary expense up front and can cost you much more in the long run.
Ted: first a small correction: Higher percentage of long chain HC will decreases the octane index. Indeed, the root cause of spontaneous detonation is those long chains would uncontrollably break under high pressure/temperature. For example, here is the table of research blending octane (RON) of each major HC component for petrol:
As you can see, the longer is the chain, the worse is the octane index. On the side note, the high percentage of aromatic HC (where the C atoms are connected like a ring and not like a chain) is good for high octane, because they are very solid molecules. During the distillation, gasoline are separated into three groups (from lightest to heaviest, shortest chain to longest chain): petrol, kerosene, and gasoil. In fact, the petrol is the most demanded, and refineries have to make the so-called "cracking procedure" in order to break the long HC into smaller molecules found in the petrol.
Now back to the flame speed. To be totally correct, the flame speed depends on engine RPM. It burns faster at higher RPM. On the top of my head, the two significant factors that control the flame speed is the turbulence (swirl) of the air/fuel mixture inside the combustion chamber and the ERG. More there is the swirl, faster is the flame. More there is ERG, slower is the flame. High rpm induces more swirl and less ERG. These two factors are part of the design of the engine. The other factor (much less important) that controls the flame speed is the chemistry components that make up the fuel. This is what you are talking above. In the unleaded gasoline we buy, the additive that uses to enhance the octane index is typically Methyl Tertiary Butyl Ether (MTBE). The percentage of MTBE is small and doesn't change significantly the chemistry HC components of the fuel. Thus the flame speed remains more or less the same regardless the octance index of the petrol. To prove the point, for example high octane racing fuels designed for high rpm applications tend to have higher flame speeds than normal to help reduce burn time. It's important to have quick flame speed when the engine is running constantly at 10000 rpm. Making the correlation between flame speed and octane is a most common misconception I have seen while reading on the internet.
I said I was oversimplifying when referring to the long chain HCs. I am aware that iso-octane, etc. are not linear HC chains. I was making a point about energy density. Assuming a similar flame speed for Premium and Regular, premium will still have more unburned HCs since it takes longer to combust the same amount of a fuel with a higher energy density. Flame speed and combustion rate are not the same for any material. Knock resistance is the main reason race fuels are 104+ octane. Have you ever seen the amount of unburned HCs coming out of a racecar's exhaust? Race fuels burn very slow, but can withstand the diesel-like compression ratios. There is a good reason no manufacturer produces a car that requires more than 91 octane. Emissions becomes a problem beyond that point -- specifically, unburned HCs and Nitrogen compounds which produce smog. One reason CART cars run on methanol is to reduce these emissions. The oil companies can tell us all day long that it is OK to put more expensive fuel in our cars, but I do not buy it. I totally depends on the car and how it is driven. Street cars do not have the same sort of swirl created in their combustion chambers that race cars have because the necessary equipment is very expensive to produce. I have seen the results, and they are not pretty. Sludgy would be a better word.
I say we agree to disagree. I think one thing we can agree on is that the Mazda3 does not require, nor will receive any benefit from plus or premium fuel. It would be a waste of money. It would be better to spend that money on a fuel with better than average additives, like Chevron. At least that way your engine would tend to stay clean.
Have you ever seen the amount of unburned HCs coming out of a racecar's exhaust?
Yes. But I believe the main reason is: engines of racecar are always rich-tuned. It is well known that rich-tuned (air/fuel ratio < 12) optimise performance whereas lean-tuned (air/fuel > 16) optimise engine efficiency. Our cars operates around 14.5 (The above also explains why performance is usually incompatible with emission, unfortunately. There is another reason and I'll explain shortly).
There is a good reason no manufacturer produces a car that requires more than 91 octane
Another good reason is the distilled cost increases exponentially with the octane index.
Emissions becomes a problem beyond that point -- specifically, unburned HCs and Nitrogen compounds which produce smog.
The Nox has nothing to do with flame speed. In normal combustion, the result of Air (O2+N) and fuel (HC) burning is H20+C02+N (unchanged N). Unfortunately, for the very high temperature environment, Nitrogen tends to combine with Oxygen and creates N0 as by-product. Under sunlight, N0 combines with another oxygen molecule and creates N02, and eventually derives smog. Because high octane gas is used in high compression-ratio engine, thus the combustion is performed at higher temperature. This in turn give more smog than low-octane gas. But for the exact same engine, the amount of smogs produced by high and low octane fuel should be similar.
Pardon for interrupting the conversation, but does anyone have any information or thoughts as to the introduction of traction control (and heated seats) for the 3? That's all I think they missed out on in the 3's release.
And as for the Mazdaspeed, other than what was reported last month regarding the 3 being the next Mazdaspeed model, any more info or conjecture out there?
I finally sat in a 3 while having my P5 serviced this past week, and was left reconsidering my desire to get a Mini next time round...the 3 is just that gorgeous inside.
Comments
I've noticed some good and bad things about the hatch...What I DO like is the compartment storage area underneath the floor. THAT is useful. I've got my booster cables, spare oil bottles, wrench, etc. all stored there, and it doesn't get in the way. Kudos to Mazda on that one. It's very well thought out.
But I don't like the hatch cover.. IMO, it is bad, especially when I tried leaning over to get something deep in the trunk, and got my eyelid scratched on the cover?!? The edge is TOO sharp.
Not only that, It took me only 1 day after purchase when I realized, I was not getting the trunk space I needed (strollers, large bags, etc). It would be cool if there was some convenient place IN the car, where I could quickly store it, but there isn't. So now it's sitting in my basement! What a useless device.
Did anyone who bought the hatchback actually keep the hatch cover in place?
Well, the good news is that someone's aftermarket rack will fit the car. Now, I just need to do a little investigative work to figure whose it is, since Thule and Yakima aren't claiming it.
Thanks again.
Rick
If my wife wants to go shopping in her P5 (for anything that might tempt thieves and isn't bulky), she takes the cover with her.
It wouldn't have been as sturdy but I would have preferred one of those roll-up covers like I've seen in some SUV's. Just roll it into a tube and push the seats forward. Then there's the back-seat headrests.......
I've got just over 1000kms on my 3 Hatch and I can already see wear in the outside of the tires. "Nibs" are rubbed out as well. And I'm not all that "spirited" a driver. Especially in Januaruy. This could get costly.
Rick
I called a few dealers for prices and yes as you said the mirror turns out to be too damn expensive for the part and installation. Too bad I have to forget about it
One dealer estimated $112 for installing the cassette player. From what you are saying, it should be very eaasy to install - do you think we can do it ourselves?
Ted
Ted
http://home.att.net/~mazda3s/Mazda3.pdf
but how does higher octane lead to carbon build up?
The job of fuel components which define "octane" , simply put, is to stop premature piston firing. Higher performance engines run hotter, so they need a higher octane to stop the pistons firing before they should. This is the most simplistic, yet the most accurate way of putting it (exceptions aside of course).
Now for engines that aren't so high powered...say a 1.7L Honda Civic, they are fine to run on Octane Grade 87. You can run them on Octane 91, or even Octane 94. Will it make a difference? No. But it should not harm the engine, so far as I know. If this is not the case, please enlighten.
Now, the only case I've heard of where one should run Octane 89 or 91 on a car that says it can get by on Octane 87 are those advanced higher performance engines with octane sensors. In these cases (I think Acura has 1 or 2 models like this), the motor runs better on Octane 89/91 because it wants to run hotter, but if it detects Octane 87, it will downgrade performance to keep the engine cooler, so that the engine won't knock.
Oh, there is one more more situation:
- if you are going on a long road trip where there are lots of hill, and your vehicle is loaded to max towing capacity, then I've heard it's a good idea to upgrade to Octane 89 in case one's engine gets too hot (combatting those hills).
Other than that, upgrading to a higher octane is a waste of money. Some "premium" fuels have more cleaning additives/ethanol/etc which can be somewhat beneficial to run continuously 2 weeks before an emissions test, but the higher octane they provide generally speaking do nothing in and of themselves for most cars that are Rated to run 87.
Higher compression can also be a factor in need for higher octane. I just don't see how using higher octane can lead to carbon build-up in an engine (rated for lower octane).
Waste of money? Most of time. Harmful? No way..
But if someone has info to the contrary, please reply.
Ted
Bruno
In order to take advantage of the high octane gas, one needs two things in the design:
1) high compression ratio
2) "aggressive" (i.e., early) spark-plug timing.
Such design can still use lower octane gas, by adjusting the spark-plug timing, thanks to the anti-knock sensor.
Mazda3 Australia-spec can do this (but the engine efficiency is crappy when using regular gas).
The way I understand it, N/A Mazda3 engines is tuned for regular gas. It doesn't have both characteristic 1) and 2). So, no, it can't take advantage of higher octane gas. But when runing with regular gas, N/A-spec Mazda3 is more efficient than AU-spec Mazda3.
When I was visiting Colombie 2 years ago, I got to drive a P5 with 1.4L engine and drum rear brake!
Some S.A. countries still sell the 323 and 626!
Couldn't find a web site for Mexico at all. They make the engines but don't sell the cars there?
Even though the flame front can ignite the whole volume of the cylinder in the time it takes for 60° of crankshaft rotation, it isn't necessarily a complete burn. Since premium burns slower, an incomplete burn will produce more unburned material than regular in an engine designed for regular.
Ted
I don't think it's accurate to say Higher Octane fuels "burn slower".
They certainly don't prematurely ignite at lower temperatures as easily (that's the point). But when the spark plug provides the ignition source, combined with the enormous compression pressures, Octane 91 gas will burn up just as easily as Octane87. There really should be no excess carbon buildup for Octane 91 over and above what you'd see for Octane87. Naturally, there will be excess hydrocarbons produced, but that would happen in any event. Ted, I think your concerns relate more to alternative fuels which may not work at the compressions pressures, temperatures, and spark level seen in gasoline engines.
Here is what a professor at the University of Missouri says (keep in mind he's talking about "hard" drivers):
and here's the link: http://www.missouri.edu/~news/archives/tipsarchive/july00tip.html
--------------------------------------
Paying Higher Prices for Premium Gas at the Pump May be Worth It
With gas prices today as high as they are, people are looking to cut corners to save at the pump. While choosing a lower grade of fuel might help to reduce costs in the short run, a University of Missouri-Columbia professor says that it sacrifices engine performance and could have adverse effects on the life of the engine.
Premature ignition in the engine, also known as knocking, occurs when the engine isn't running properly. The way to minimize this problem is to raise the octane level of the gasoline, said Bob Tzou, an MU professor of mechanical engineering. Octane helps the engine resist premature ignition. The higher the octane level in the gas, the better.
Contaminants in the engine often result from premature ignition, leading to an increase in chemical residues. Over time, this incomplete combustion can have adverse effects on the life and performance of the engine, costing a car owner much more in repairs.
Tzou suggests these five tips when filling up your car:
Always use the highest possible octane gas if price is not a major concern. This is particularly the case if you want to keep your car for a long time.
Fuel your tanks by high-octane gas if the engine is working hard. Heavy-load towing, long-distance driving and hot summer days are typical examples.
An older engine may be more sensitive to the octane number than a new engine. Upgrade the octane number to the next level (for example, from 87 to 89 or from 89 to 91) if you find the car that you have driven since new starts to knock on the road. This usually happens in hard-working conditions described above.
High-octane gas always should be used by aggressive drivers who love the thrill of acceleration. The price for the thrill increases as the price of premium gas increases.
If you have been using 87-octane gas and knocking has not happened, use a no-lead fuel injector (carburetor) and engine cleaner to prevent chemical buildups, due to possible premature ignition. This is particularly important if the engine is old. This product is available in supermarkets and many gas stations. - Ben Kampelman
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I live at 5000 feet altitude, and regular is 86 octane instead of 87. I believe this is done to maintain low emissions with less oxygen available. To me, this 1 point octane difference demonstrates the delicacy of the balance between performance, efficiency, and emissions.
You know why? This is classic. Because gas companies want to save $$$, that's all.
On high altitude, for the same car, the octane requirement is less. Here is few factors that require higher octane:
- high pressure -> low altitude, turbo engine, compressor, high compression ratio.
- high temperature -> summer
- high engine load -> going uphill, lug the engine
PS: I was working for oil company!
I drove to the top of Pikes Peak once (14,110ft). Yeah, the car got real slow at the top. Incidently, the US military tested early aircraft turbos up there.
Q: What octane would be required at 20000ft?
A: It doesn't matter as the car probably wouldn't run anyway.
There is no performance enhancement that correlates to octane number - it only refers to its ability to resist knocking.
Some auto manufacturers (especially Nissan) are running a very nice scam. They engineer their cars to run best on 91 octane fuel. Most manufacturers would just smack on a label telling the owner to use only unleaded premium (91 or higher) gas. No, they don't do that. To qualify their cars as 'regular gas' consumers, they equip their cars with knock sensors to avoid premature ignition and compensate by firing the spark plugs earlier and reducing engine performance at the same time if the user uses fuel with a lower octane number - even 87. Why do they do this? So they can advertise their cars as using 87 octane gas for penny pinchers. All the while, their cars will run best on 91 or higher octane fuels.
Now, most manufacturers now equip their cars with similar knock prevention devices, but these are meant to save the engine in the case of low octane fuel being used by accident. There is no reverse system that enhances performance by using fuel with a higher octane number.
The Mazda3 and most cars that simply request 87 octane will run best with that fuel and any higher octane is just money out the window. If you want to make damn sure that you never drop below 87 by some rare fluke, sure use 89 as an insurance policy - but don't expect any perfomance increase or longevity issues with that.
The gas companies are promoting high octane as high performance. It's a sales pitch. This is just not true. Sure some high-performance (read as high-compression) engines need high octane, but this is for knock resistance, not added performance.
The normal flame speed is fairly consistent for most gasoline HCs, regardless of octane rating, but the flame speed is affected by stoichiometry.
So guskim is right, the higher octane will not burn slower. Even it's slower, it's not that critical.
http://www.nsf.gov/nstw_questions/chem/quest025.htm
Flame speed is generally not an important parameter for engine operation, as long as the flame can reach the boundaries of the cylinder during the proper part of the cycle.
And as my simple calculation above shows, there is plenty of time for the flame to reach the entire cylinder.
I agree that there is no need to run the Mazda3 on higher octane. In fact, I've said quite a few times that it's probably a waste of money
It's just that I don't think the higher Octane of 89 or 91 will HURT the engine in terms of carbon buildup. In effect, for the Mazda3 engine, Octane 87 through 91 should make NO difference (positive or negative).
(unless one REALLY drives the car hard up hills all the time with the vehicle fully loaded with payload).
I have a RSX type S and was thinkig of getting the Maxda Hatch. Will I be Disappointed (Torque )?Iv'e priced them out also and it comes close to 20K.
Please enlighten me.
Are there enough unburned hydrocarbons generated in a single crankshaft rotation to cause carbon buildup? No.
At an average engine speed of 3000 RPMs over the course of the first few years a motor is in service, will premium fuel in an engine not designed for it cause carbon buildup from an excess of unburned hydrocarbons? It could. More so if you keep the engine higher in the rev range.
This is all my opinion which is based on my understanding of chemistry (5 semesters in college including Organic and Geochemistry plus a Chemist wife) and what I have seen in the last few years from people using premium in cars that do not need it, thinking they are getting more power from it. Why do you think repair shops sell so many engine cleaning services? It is an unnecessary expense up front and can cost you much more in the long run.
Ted
butane (4C) 113
pentane (5C) 62
hexane (6C) 19
heptane (7C) 0 (by definition)
octane (8C) -18
As you can see, the longer is the chain, the worse is the octane index. On the side note, the high percentage of aromatic HC (where the C atoms are connected like a ring and not like a chain) is good for high octane, because they are very solid molecules. During the distillation, gasoline are separated into three groups (from lightest to heaviest, shortest chain to longest chain): petrol, kerosene, and gasoil. In fact, the petrol is the most demanded, and refineries have to make the so-called "cracking procedure" in order to break the long HC into smaller molecules found in the petrol.
Now back to the flame speed. To be totally correct, the flame speed depends on engine RPM. It burns faster at higher RPM. On the top of my head, the two significant factors that control the flame speed is the turbulence (swirl) of the air/fuel mixture inside the combustion chamber and the ERG. More there is the swirl, faster is the flame. More there is ERG, slower is the flame. High rpm induces more swirl and less ERG. These two factors are part of the design of the engine. The other factor (much less important) that controls the flame speed is the chemistry components that make up the fuel. This is what you are talking above. In the unleaded gasoline we buy, the additive that uses to enhance the octane index is typically Methyl Tertiary Butyl Ether (MTBE). The percentage of MTBE is small and doesn't change significantly the chemistry HC components of the fuel. Thus the flame speed remains more or less the same regardless the octance index of the petrol. To prove the point, for example high octane racing fuels designed for high rpm applications tend to have higher flame speeds than normal to help reduce burn time. It's important to have quick flame speed when the engine is running constantly at 10000 rpm. Making the correlation between flame speed and octane is a most common misconception I have seen while reading on the internet.
Bruno
ERG should be read EGR (Exhaust Gas Recirculation)
I say we agree to disagree. I think one thing we can agree on is that the Mazda3 does not require, nor will receive any benefit from plus or premium fuel. It would be a waste of money. It would be better to spend that money on a fuel with better than average additives, like Chevron. At least that way your engine would tend to stay clean.
Ted
Yes. But I believe the main reason is: engines of racecar are always rich-tuned. It is well known that rich-tuned (air/fuel ratio < 12) optimise performance whereas lean-tuned (air/fuel > 16) optimise engine efficiency. Our cars operates around 14.5 (The above also explains why performance is usually incompatible with emission, unfortunately. There is another reason and I'll explain shortly).
There is a good reason no manufacturer produces a car that requires more than 91 octane
Another good reason is the distilled cost increases exponentially with the octane index.
Emissions becomes a problem beyond that point -- specifically, unburned HCs and Nitrogen compounds which produce smog.
The Nox has nothing to do with flame speed. In normal combustion, the result of Air (O2+N) and fuel (HC) burning is H20+C02+N (unchanged N). Unfortunately, for the very high temperature environment, Nitrogen tends to combine with Oxygen and creates N0 as by-product. Under sunlight, N0 combines with another oxygen molecule and creates N02, and eventually derives smog. Because high octane gas is used in high compression-ratio engine, thus the combustion is performed at higher temperature. This in turn give more smog than low-octane gas. But for the exact same engine, the amount of smogs produced by high and low octane fuel should be similar.
Yes, we have to agree to disagree.
Bruno
And as for the Mazdaspeed, other than what was reported last month regarding the 3 being the next Mazdaspeed model, any more info or conjecture out there?
I finally sat in a 3 while having my P5 serviced this past week, and was left reconsidering my desire to get a Mini next time round...the 3 is just that gorgeous inside.
Thanks.