Cumulative Synthetic Oil Discussion
03-04-2010, 05:10 PM
#1178
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There is more than one standard of what should be put into gasoline (some of them refer to it as "petrol"). Also, there are different ways of measuring the octane rating, and different ratings are common in different markets - just as engines designed in different continents tend to have different compression ratios.
So much for generalities. D'you know specifically how the fuel from the Japanese market compares with that in the US? I don't. But to me it seems reasonable that, when considering what goes on inside the combustion chamber of these engines, the formulation of the fuel might have as much effect as that of the oil. Of course I may be quite mistaken about that, in which case I'm happy to be enlightened, though if possible I'd prefer that not to involve gratuitous profanity.
So much for generalities. D'you know specifically how the fuel from the Japanese market compares with that in the US? I don't. But to me it seems reasonable that, when considering what goes on inside the combustion chamber of these engines, the formulation of the fuel might have as much effect as that of the oil. Of course I may be quite mistaken about that, in which case I'm happy to be enlightened, though if possible I'd prefer that not to involve gratuitous profanity.
03-06-2010, 06:51 PM
#1180
Big cities with air quality issues are apparently shipped the cleanest fuel, according to the article. All this, as specifed by the EPA.
Before anybody says that there are standards, yes there are, but if I recall correctly, the cleanliness had to do with several factors, some of it where the oil was distilled.
It got enough attention that one of our Senators started making noise. Not sure what came of it, though.
So it would appear that not all gas is the same, even within a given region.
03-09-2010, 02:30 AM
#1183
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Not to go too far OT, but in regards to octane; a member from Puerto Rico explained to me that the main reason to use high octane fuel in a rotary is that it burns more efficiently and thus produces lower heat in the combustion chamber. I haven't found any other members who have confirmed or refuted this, but it seems logical.
you really believe that, don't you?
03-09-2010, 10:42 AM
#1186
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Not to go too far OT, but in regards to octane; a member from Puerto Rico explained to me that the main reason to use high octane fuel in a rotary is that it burns more efficiently and thus produces lower heat in the combustion chamber. I haven't found any other members who have confirmed or refuted this, but it seems logical.
If your engine was capable of using 89 without knocking beforehand, using 93 and then going to 89 won't change the fundamental characteristics of your engine.
Last edited by JinDesu; 03-09-2010 at 10:44 AM.
03-09-2010, 10:50 AM
#1188
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Should we use 87 octane just because RX-7s were able to do so? Well, that's up to you, isn't it?
03-09-2010, 10:56 AM
#1189
but per, you...
So guess wildly again as to why higher octane fuel may be considered for use in the Renesis.
Last edited by mac11; 03-09-2010 at 11:00 AM.
03-09-2010, 11:01 AM
#1190
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Alright - I apologize if I came off as explaining why the RX-8 uses 93 octane incorrectly. I stepped in only to explain the difference between octane levels - energy required to detonate it. By saying "oddly shaped chamber", I mis-spoke.
Here goes my wild guess: Why does my Renesis use 93 octane? Because I've heard that our knock-sensors are useless. Does the RX-7 have better knock sensors? I don't know, I don't have an RX-7.
To my knowledge, the improvement of power from using higher octane levels is not the octane itself, but the tune. By fine tuning the fuel combustion process to an exact degree, we get the maximum power from it. Higher octane gas, with their ability to resist premature detonation, is critical to it. That was the only point I originally wanted to make.
Here goes my wild guess: Why does my Renesis use 93 octane? Because I've heard that our knock-sensors are useless. Does the RX-7 have better knock sensors? I don't know, I don't have an RX-7.
To my knowledge, the improvement of power from using higher octane levels is not the octane itself, but the tune. By fine tuning the fuel combustion process to an exact degree, we get the maximum power from it. Higher octane gas, with their ability to resist premature detonation, is critical to it. That was the only point I originally wanted to make.
is that what you're getting at?
03-09-2010, 01:54 PM
#1195
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I have an RX-7 and I run only 87 octane. The car loves it. Why does the Renesis not like lower octane? Simple. Tuning. It's not the compression ratio. 9.7:1 in my car and 10.0:1 in a Renesis is not enough to matter. Back timing off a few degrees and the Renesis could burn it just fine. Incidentally the Renesis runs more advance than my car does. Max advance at full throttle for me is 26 degrees. It's 30 for a Renesis. Max advance under light throttle/cruise for me is about 36 degrees. For a Renesis it's in the 40's. See the correlation?
It really comes down to emissions. Each octane burns at the same speed. A higher resistance to detonation means that timing can be adjusted to burn it longer which means cleaner. Not necessarily noticably more power although a little is probable. Flame front travel takes time. You want it expanding at it's max rate as the engine is passing TDC. However due to flame speed we need to light it earlier than that so that it reaches peak pressure around then. If there is a propensity to detonate we can't ignite it this soon. This means we'll waste a little bit on the back side hence the "little" amount of probable power gain but more importantly it was this small extra amount of time to get more of the fuel and hence emissions burned off. A hp or two doesn't really matter but when it comes to emissions, every gram does. Based on flame speed we can see that for every fuel only so much octane is useful in any certain engine configuration. Above that it doesn't help anymore. It of course is different for boosted or nonboosted cars, different boost levels, etc.
It really comes down to emissions. Each octane burns at the same speed. A higher resistance to detonation means that timing can be adjusted to burn it longer which means cleaner. Not necessarily noticably more power although a little is probable. Flame front travel takes time. You want it expanding at it's max rate as the engine is passing TDC. However due to flame speed we need to light it earlier than that so that it reaches peak pressure around then. If there is a propensity to detonate we can't ignite it this soon. This means we'll waste a little bit on the back side hence the "little" amount of probable power gain but more importantly it was this small extra amount of time to get more of the fuel and hence emissions burned off. A hp or two doesn't really matter but when it comes to emissions, every gram does. Based on flame speed we can see that for every fuel only so much octane is useful in any certain engine configuration. Above that it doesn't help anymore. It of course is different for boosted or nonboosted cars, different boost levels, etc.
03-10-2010, 07:42 AM
#1196
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Thank you for the good explanation. How did you decide what was a good octane for your car? When I had a turbo/piston engine, it had good knock sensors, so I could monitor if it knocked. During the winter I would lower the octane since it was cooler and I drove it less hard. With the rotary I understand that the knock sensor isn't very helpful; and my hearing isn't as good as it once was. This winter I have tentatively lowered octane and never heard knocking, but I always went back to premium (I can get it with no ethanol) for fear of not being sensitive to the engine knocking. (I have also checked several times to see if timing was being retarded by the knock sensor - it wasn't.)
I am not asking to save money on gas. I have always heard that too much octane leads to carbon buildup. Also, if it is true the engine runs cooler with higher octane, my engine runs too cool during the winter (massive condensation in my oil even though I don't drive short trips and I have my oil coolers covered).
I am not asking to save money on gas. I have always heard that too much octane leads to carbon buildup. Also, if it is true the engine runs cooler with higher octane, my engine runs too cool during the winter (massive condensation in my oil even though I don't drive short trips and I have my oil coolers covered).
03-10-2010, 09:41 AM
#1197
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Older n/a rotaries always loved low octane. They were tuned for it. The tag on my gas door states 87 octane or higher. Times have changed and so have emissions regulations. On a turbo rotary I wouldn't be inclined to use 87 octane although you could if stock power levels were kept. Many rotary race teams used to use low octane. Today they use 96 per the rules.
Higher octane shouldn't have any affect on carbon buildup. Technically the reverse would theoretically be true although I doubt it's measureable. Octane also shouldn't affect the heat rejection properties of gasoline.
One thing that I'm surprised that no one has tried is a water separator in the oil system. It wouldn't be hard to do. It would just look like another oil filter mounted somewhere else. Although typically used in diesel fuel systems, diesel fuel really is just a light oil so I don't know why it wouldn't work. I'd love to see it at least tried.
Higher octane shouldn't have any affect on carbon buildup. Technically the reverse would theoretically be true although I doubt it's measureable. Octane also shouldn't affect the heat rejection properties of gasoline.
One thing that I'm surprised that no one has tried is a water separator in the oil system. It wouldn't be hard to do. It would just look like another oil filter mounted somewhere else. Although typically used in diesel fuel systems, diesel fuel really is just a light oil so I don't know why it wouldn't work. I'd love to see it at least tried.
03-11-2010, 03:11 AM
#1199
Originally, the RX8 manual said 87 gas was fine. The RX8 uses 93 because some RX8 owners in 04 where experiencing knock. It was easier for Mazda to say use 93 then to explain if you have knocking use higher octane fuel.
I do believe using 93 for long periods of time and then using a low octane ga will cause some knocking. Why do I believe it? It happened to me. After I reset the removed the room fuse and reset the fuel trims, it was able to compensate faster and I did not get the knock.
I do believe using 93 for long periods of time and then using a low octane ga will cause some knocking. Why do I believe it? It happened to me. After I reset the removed the room fuse and reset the fuel trims, it was able to compensate faster and I did not get the knock.
the 04 manual just say premium is recommended.. and performance will be reduced if you dont use it..
and correct on you comments about ltft..
my car drives daily on 87. no knock no problems. always has.. has put down some good dyno #s on it also..
but for track events.. 94 and pull the room fuse.. safety!
beers
Last edited by swoope; 03-11-2010 at 03:14 AM.
03-11-2010, 06:24 AM
#1200
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One thing that I'm surprised that no one has tried is a water separator in the oil system. It wouldn't be hard to do. It would just look like another oil filter mounted somewhere else. Although typically used in diesel fuel systems, diesel fuel really is just a light oil so I don't know why it wouldn't work. I'd love to see it at least tried.