Optimal Fuel / Octane Question
02-09-2004, 02:17 AM
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Optimal Fuel / Octane Question
I read in the manual, that while Mazda recommends premium fuel with an octane rating of 91 and higher, one can use a lower grade fuel with an octane rating of between 87 - 91. Mazda implies that there will be no damage (aside from a slight loss in performance), if fuel with an octane rating of 87 - 91 is used. I know that the difference between "premium" fuel and "plus" fuel is only marginal at times, but considering the high gas prices nowadays, would it be out of the question for me to even consider using fuel with a lower octane level than 91?
02-09-2004, 05:30 AM
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im going with the manual, ive been using 93 octane since i first bought the car. The car even came with 93 octane when it arrived. Other members stated how its useless to use 91+, then why would mazda write it on the manual? I never had rough idle and never had flooding since ive warmed up my car before i let it loose. Basically for choosing the right octane, its your choice.
02-09-2004, 06:21 AM
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I just want to make sure everyone agrees, that aside from the performance differences, using fuel with either a rating of 87 or 89 will not damage the engine or have any other adverse affects in any way. Besides, saving some money on gas wouldn't hurt either...
02-09-2004, 08:55 PM
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Re: Optimal Fuel / Octane Question
Hi DavisRx8,
Check out the "87 Octane - the answer to idle?!?" thread for more views on the subject.
I've been using 87 octane (usually Shell) for about 4k miles with no problems. I'm only doing this because the manual says we can do so as you pointed out ...... and I don't feel the need for the personally unmeasurable performance or expense of 91+ octane.
regards,
rx8cited
Check out the "87 Octane - the answer to idle?!?" thread for more views on the subject.
I've been using 87 octane (usually Shell) for about 4k miles with no problems. I'm only doing this because the manual says we can do so as you pointed out ...... and I don't feel the need for the personally unmeasurable performance or expense of 91+ octane.
regards,
rx8cited
02-10-2004, 02:36 AM
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After reading the numerous posts regarding the use of 87 octane, I decided to put it to the test as well. I'm going to keep a detailed log regarding startup, smoothness of idling, fuel efficiency, power/performance, tone, and sootiness of the exhaust. I'll keep everyone posted with my results.
02-17-2004, 02:22 AM
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Results Post #1 (2/16/04) - Results compiled through 3 cycles - full tanks - of 87 Octane usage.
1. Startup: Definite Improvement without a doubt. While I was using 91 Octane fuel, my startups were shakey from time to time, especially if it was cold out. There were times, when I would fail at my first attempt to start the car - it would sound as if the spark plugs were not firing correctly - and have to wait a few minutes before successfully engaging the engine. While I am no expert on the association between octane levels and engine ignition, I can say from my observations, that the startups are much cleaner and "confident" sounding. Bottom line: Excellent improvement.
2. Smoothness of Idle: I noticed that my shift **** (most noticeably among others) vibrates at idle, more so than I am used to in my former protege and in my sister's civic. I initially thought it was normal for all Rx-8's (per my dealer's insistence) to have that vibration. After reading some member's post, I realized that we experience vibrations at idling to differing degrees - some people have an uncomfortable level of vibration, while others claim to have none. I of course realize that individuals have differing levels of tolerance, and differing experiences with differing levels of vibrations in differing vehicles (whew). Once again, while I had no idea what relevance a lower octane level would have with vibration levels, I decided to keep to my empirical self study and keep a log of my observations. Results...an improvement, but not as substantial of an improvement as seen in my startup. The shift **** (including general vibration throughout the chasis), does vibrate noticeably less, however, the vibration is still there. Point of observation --> I've read this somewhere on another thread, but my car seems to vibrate more as it idles at 800 rpm, as opposed to 1000 or 1100 rpm. Essentially, it seems to vibrate more when the car is fully warmed up! Bottom line: General Improvement, but not substanially so.
3. Power/Performance/Smoothness: The general performance of the car IS reduced. My 8 doesn't quite have that same kick that it did running from idle to about 4000 rpm (the point where I generally shift with normal driving). Not to say that I'm crawling around; I can still pass circles around most cars if I feel like doing so. The trade-off from my SLIGHT loss of performance is the increased smoothness of acceleration. With the 91 octane, the car jumped forward aggressively (alright people, I was driving a 2000 protege LX before - not exactly a rocket). With the 87 octane, the acceleration, while not as aggresive, is much more refined seeming. Bottomline: Performance or smoothness? Personal opinion I guess. When I experience my "need for speed...right now" I'll just temporarily switch back to 91 octane.
4. Tone: The sound of the car is different, although not substantially so. Similar to the increased smoothness in response and acceleration, the tone - subsequently? - smoothed out as well, and became a tad bit higher pitched. The best example I can give is that it sounds more "airy" as opposed to "rumbly." Or at least as "rumbly" as a rotary can possibly sound. Perhaps the sound of the rotary is somehow more defined? Bottomline: I just like how the rotary sounds in general...higher pitced, lower pitched...still rotary!
5. Sootiness of Exhaust: Before my initial testing, I wiped the interior and exterior of my exhaust tips of all soot. After 3 tanks of 87 octane, I did notice that the exhaust tips were sooty, but not nearly as much as they were before. I do understand that I am comparing 2000 miles driven on 91 octane with less than 800 driven on 87 octane! Bottomline: Need more time to come to any relevant results.
6. MPG/ Fuel efficiency: I am one of those 8 owners you read bit**ing about the horrendous mpg. Since the day I bought my 8, I consistently averaged between 12 -14 mpg with 70% city and 30% hwy driving. While it's nothing to boast over - considering the 24's that some people are getting - my mpg has increased to between 15 - 17 mpg with the same distribution of city to hwy driving with using 87 octane. I realize that my study isn't very empirical considering the uncontrollable variables involved - for one, perhaps I WAS driving less aggresively to somehow justify and live up to the expectations I had for 87 octane to positively affect my ride. Regardless, I am thrilled at the increased mpg. ::grins sheepishly:: Bottomline: Definite Improvement. 200 mp[tank] --> 250 mp[tank].
*I'm going to conduct my study and post every 3-5 tank. I'll post my results on returning to 91 octane as well.
1. Startup: Definite Improvement without a doubt. While I was using 91 Octane fuel, my startups were shakey from time to time, especially if it was cold out. There were times, when I would fail at my first attempt to start the car - it would sound as if the spark plugs were not firing correctly - and have to wait a few minutes before successfully engaging the engine. While I am no expert on the association between octane levels and engine ignition, I can say from my observations, that the startups are much cleaner and "confident" sounding. Bottom line: Excellent improvement.
2. Smoothness of Idle: I noticed that my shift **** (most noticeably among others) vibrates at idle, more so than I am used to in my former protege and in my sister's civic. I initially thought it was normal for all Rx-8's (per my dealer's insistence) to have that vibration. After reading some member's post, I realized that we experience vibrations at idling to differing degrees - some people have an uncomfortable level of vibration, while others claim to have none. I of course realize that individuals have differing levels of tolerance, and differing experiences with differing levels of vibrations in differing vehicles (whew). Once again, while I had no idea what relevance a lower octane level would have with vibration levels, I decided to keep to my empirical self study and keep a log of my observations. Results...an improvement, but not as substantial of an improvement as seen in my startup. The shift **** (including general vibration throughout the chasis), does vibrate noticeably less, however, the vibration is still there. Point of observation --> I've read this somewhere on another thread, but my car seems to vibrate more as it idles at 800 rpm, as opposed to 1000 or 1100 rpm. Essentially, it seems to vibrate more when the car is fully warmed up! Bottom line: General Improvement, but not substanially so.
3. Power/Performance/Smoothness: The general performance of the car IS reduced. My 8 doesn't quite have that same kick that it did running from idle to about 4000 rpm (the point where I generally shift with normal driving). Not to say that I'm crawling around; I can still pass circles around most cars if I feel like doing so. The trade-off from my SLIGHT loss of performance is the increased smoothness of acceleration. With the 91 octane, the car jumped forward aggressively (alright people, I was driving a 2000 protege LX before - not exactly a rocket). With the 87 octane, the acceleration, while not as aggresive, is much more refined seeming. Bottomline: Performance or smoothness? Personal opinion I guess. When I experience my "need for speed...right now" I'll just temporarily switch back to 91 octane.
4. Tone: The sound of the car is different, although not substantially so. Similar to the increased smoothness in response and acceleration, the tone - subsequently? - smoothed out as well, and became a tad bit higher pitched. The best example I can give is that it sounds more "airy" as opposed to "rumbly." Or at least as "rumbly" as a rotary can possibly sound. Perhaps the sound of the rotary is somehow more defined? Bottomline: I just like how the rotary sounds in general...higher pitced, lower pitched...still rotary!
5. Sootiness of Exhaust: Before my initial testing, I wiped the interior and exterior of my exhaust tips of all soot. After 3 tanks of 87 octane, I did notice that the exhaust tips were sooty, but not nearly as much as they were before. I do understand that I am comparing 2000 miles driven on 91 octane with less than 800 driven on 87 octane! Bottomline: Need more time to come to any relevant results.
6. MPG/ Fuel efficiency: I am one of those 8 owners you read bit**ing about the horrendous mpg. Since the day I bought my 8, I consistently averaged between 12 -14 mpg with 70% city and 30% hwy driving. While it's nothing to boast over - considering the 24's that some people are getting - my mpg has increased to between 15 - 17 mpg with the same distribution of city to hwy driving with using 87 octane. I realize that my study isn't very empirical considering the uncontrollable variables involved - for one, perhaps I WAS driving less aggresively to somehow justify and live up to the expectations I had for 87 octane to positively affect my ride. Regardless, I am thrilled at the increased mpg. ::grins sheepishly:: Bottomline: Definite Improvement. 200 mp[tank] --> 250 mp[tank].
*I'm going to conduct my study and post every 3-5 tank. I'll post my results on returning to 91 octane as well.
Last edited by DavisRx8; 02-17-2004 at 02:35 AM.
02-18-2004, 09:34 AM
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Originally posted by DavisRx8
Results Post #1 (2/16/04) - Results compiled through 3 cycles - full tanks - of 87 Octane usage.
2. Smoothness of Idle: I noticed that my shift **** (most noticeably among others) vibrates at idle, more so than I am used to in my former protege and in my sister's civic. I initially thought it was normal for all Rx-8's (per my dealer's insistence) to have that vibration. I realized that we experience vibrations at idling to differing degrees - some people have an uncomfortable level of vibration, while others claim to have none. I've read this somewhere on another thread, but my car seems to vibrate more as it idles at 800 rpm, as opposed to 1000 or 1100 rpm. Essentially, it seems to vibrate more when the car is fully warmed up! Bottom line: General Improvement, but not substanially so.
3. Power/Performance/Smoothness: The general performance of the car IS reduced. The trade-off from my SLIGHT loss of performance is the increased smoothness of acceleration. Bottomline: Performance or smoothness? Personal opinion I guess. When I experience my "need for speed...right now" I'll just temporarily switch back to 91 octane.
4. Tone: The sound of the car is different, the best example I can give is that it sounds more "airy" as opposed to "rumbly." Or at least as "rumbly" as a rotary can possibly sound. Perhaps the sound of the rotary is somehow more defined? Bottomline: I just like how the rotary sounds in general...higher pitced, lower pitched...still rotary!
6. MPG/ Fuel efficiency: I am one of those 8 owners you read bit**ing about the horrendous mpg. Since the day I bought my 8, I consistently averaged between 12 -14 mpg with 70% city and 30% hwy driving. I WAS driving less aggresively to somehow justify and live up to the expectations I had for 87 octane to positively affect my ride. Regardless, I am thrilled at the increased mpg. ::grins sheepishly:: Bottomline: Definite Improvement. 200 mp[tank] --> 250 mp[tank].
*I'm going to conduct my study and post every 3-5 tank. I'll post my results on returning to 91 octane as well.
Results Post #1 (2/16/04) - Results compiled through 3 cycles - full tanks - of 87 Octane usage.
2. Smoothness of Idle: I noticed that my shift **** (most noticeably among others) vibrates at idle, more so than I am used to in my former protege and in my sister's civic. I initially thought it was normal for all Rx-8's (per my dealer's insistence) to have that vibration. I realized that we experience vibrations at idling to differing degrees - some people have an uncomfortable level of vibration, while others claim to have none. I've read this somewhere on another thread, but my car seems to vibrate more as it idles at 800 rpm, as opposed to 1000 or 1100 rpm. Essentially, it seems to vibrate more when the car is fully warmed up! Bottom line: General Improvement, but not substanially so.
3. Power/Performance/Smoothness: The general performance of the car IS reduced. The trade-off from my SLIGHT loss of performance is the increased smoothness of acceleration. Bottomline: Performance or smoothness? Personal opinion I guess. When I experience my "need for speed...right now" I'll just temporarily switch back to 91 octane.
4. Tone: The sound of the car is different, the best example I can give is that it sounds more "airy" as opposed to "rumbly." Or at least as "rumbly" as a rotary can possibly sound. Perhaps the sound of the rotary is somehow more defined? Bottomline: I just like how the rotary sounds in general...higher pitced, lower pitched...still rotary!
6. MPG/ Fuel efficiency: I am one of those 8 owners you read bit**ing about the horrendous mpg. Since the day I bought my 8, I consistently averaged between 12 -14 mpg with 70% city and 30% hwy driving. I WAS driving less aggresively to somehow justify and live up to the expectations I had for 87 octane to positively affect my ride. Regardless, I am thrilled at the increased mpg. ::grins sheepishly:: Bottomline: Definite Improvement. 200 mp[tank] --> 250 mp[tank].
*I'm going to conduct my study and post every 3-5 tank. I'll post my results on returning to 91 octane as well.
starting with point 2, you say that the shifter vibrates more than old front drivers you were used to: this is because there is very little insulation between your hand and the gearbox (why the shifts have so much more feeling to them), as the same metal stick you're moving is actually in the transmission moving the selector forks, rather than through a cable system (which dampens the feeling of the shifts, as well as transmission vibration).
you say in point 5 that you had expectations for the gas, and in point 3 state that the performance is reduced, but only slightly. "it doesn't seem to have that kick" says to me that this is in your head. if you can come up with a significant, measurable, and repeatable difference in performance, then you'd have reason to believe that 91 does you better than 87.
for tone, i can't think of a single example of someone's exhaust or normal combustion noises change because of a matter of a few octane points... completely different engine designs made to combust completely different fuels of course sound different, but higher and lower test gas??? again, significant (ie, not a result of changes in testing environment, or in your head), measurable, repeatable...
the biggest factor on MPG will be the way you drive the car, and whether or not your ECU is working properly (there was once a problem of a temp sender malfunctioning, and the engine would stay in "cold start" super rich mode all the time... had very seriously bad consumption numbers). i don't know if the numbers have come in for the Canzoomer modded cars, but (from the beginning, and still am if the results aren't back yet) that the consumption numbers on the modded cars (when driven comparably) will be significantly better.
all in all, i'm not trying to shoot down what you're doing, but try to allay your concerns over lower test fuel, especially ones that quite possibly mayn't even be real issues.
and Neep, things are "hard" to browse for in this forum because people can be idiots sometimes and a dozen threads will be started about the same issue... not all we mods have hours and hours and hours to burn sitting here cutting and shutting threads together, and the other side to the issue is that most newbs to the forum don't appreciate that if you really want to know about an issue, you can't sit and read for ten minutes, because no answer is ever that simple (unless it's a very basic question).
02-18-2004, 01:43 PM
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"all in all, i'm not trying to shoot down what you're doing, but try to allay your concerns over lower test fuel, especially ones that quite possibly mayn't even be real issues." (wakeech)
- No offense taken. As I said, this isn't an empirical study in any way - just my personal observations. And with all observations I make, my perception has a lot to do with the conclusions I make. And I will admit that as a "newb," in comparison to many or most people on this forum, my observtions and conclusions might/will be incorrect at times. Still a learning experiencing I think. Thanks for pointing out the "time" issue. I'll keep my posts concise in the future.
- No offense taken. As I said, this isn't an empirical study in any way - just my personal observations. And with all observations I make, my perception has a lot to do with the conclusions I make. And I will admit that as a "newb," in comparison to many or most people on this forum, my observtions and conclusions might/will be incorrect at times. Still a learning experiencing I think. Thanks for pointing out the "time" issue. I'll keep my posts concise in the future.
02-18-2004, 06:29 PM
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DavisRx8 --
Thanks for doing the testing and reporting the results. I'll be interested to read what else you report.
I started with Premium, and at 1000 miles shifted to midgrade, and I am running my first tank of (mostly) regular now at around 1700 miles. So far I haven't seen a measurable difference, except in my wallet. I plan on filling with premium once in a while, reportedly there are some benefits to detergents and other additives in the premium.
The web link given above by rx8cited does have a good discussion.
Thanks for doing the testing and reporting the results. I'll be interested to read what else you report.
I started with Premium, and at 1000 miles shifted to midgrade, and I am running my first tank of (mostly) regular now at around 1700 miles. So far I haven't seen a measurable difference, except in my wallet. I plan on filling with premium once in a while, reportedly there are some benefits to detergents and other additives in the premium.
The web link given above by rx8cited does have a good discussion.
Last edited by Trx8; 02-22-2004 at 08:34 AM.
02-18-2004, 08:34 PM
#13
Is this title ok?
The fourth post down..
https://www.rx8club.com/showthread.p...threadid=20878
This info is available at mazda electronic service information. This make me wonder those that use < 91 octance would actually experience any increase in engine noises?
https://www.rx8club.com/showthread.p...threadid=20878
A chirp or squeak may be heard at times from the engine compartment. This can occur at engine start, or during engine acceleration. The noise can easily be mistaken for a squeaky accessory drive belt.
The noise is actually caused by a slight momentary lean mixture, which results in engine detonation. (Pinging)
The RENESIS rotary engine runs much leaner than previous rotary engines, resulting in improved fuel economy and lower exhaust emissions. This momentary lean condition will not cause engine damage.
IMPORTANT!
It is important to note that customers who use low octane fuel will experience a noticeable increase in engine noise. The RX8 requires premium fuel for best performance and engine life.
FUEL: Premium unleaded fuel
Octane rating (Anti-knock index): 91 (R+M)/2 method or above (96 RON or above)
Fuel with a rating lower than 87 octane (91 RON) could cause the emission control system to lose effectiveness. It could also cause engine knocking and serious engine damage.
The noise is actually caused by a slight momentary lean mixture, which results in engine detonation. (Pinging)
The RENESIS rotary engine runs much leaner than previous rotary engines, resulting in improved fuel economy and lower exhaust emissions. This momentary lean condition will not cause engine damage.
IMPORTANT!
It is important to note that customers who use low octane fuel will experience a noticeable increase in engine noise. The RX8 requires premium fuel for best performance and engine life.
FUEL: Premium unleaded fuel
Octane rating (Anti-knock index): 91 (R+M)/2 method or above (96 RON or above)
Fuel with a rating lower than 87 octane (91 RON) could cause the emission control system to lose effectiveness. It could also cause engine knocking and serious engine damage.
02-18-2004, 09:23 PM
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Just a note on one of your points...
4. Tone: The sound of the car is different, the best example I can give is that it sounds more "airy" as opposed to "rumbly." Or at least as "rumbly" as a rotary can possibly sound. Perhaps the sound of the rotary is somehow more defined? Bottomline: I just like how the rotary sounds in general...higher pitced, lower pitched...still rotary!
-------
Your exhaust system is breaking in...the noise will generally become a little deeper and smoother regardless of octane, it's more a function of time.
4. Tone: The sound of the car is different, the best example I can give is that it sounds more "airy" as opposed to "rumbly." Or at least as "rumbly" as a rotary can possibly sound. Perhaps the sound of the rotary is somehow more defined? Bottomline: I just like how the rotary sounds in general...higher pitced, lower pitched...still rotary!
-------
Your exhaust system is breaking in...the noise will generally become a little deeper and smoother regardless of octane, it's more a function of time.
02-18-2004, 09:50 PM
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I've owned a few naturally aspirated rotaries over the past decade or so. They all ran best with the lowest octane gas. My turbo RX-7 needs high octane. I nver once felt a noticable improvement in power or drivability from higher octane. I guess the car was faster with high octane soley based off of the fact that my wallet was always much lighter at the gas station. Remember that a few horsepower isn't nearly as noticable as a few dollars every couple of days.
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