View Poll Results: Since gas is going up again.....what grade gas do you put in your C?
Always use regular unleaded
2
2.60%
Always use PLUS unleaded
1
1.30%
Always use PREMIUM unleaded
73
94.81%
Random...different grades at different times
1
1.30%
Voters: 77. You may not vote on this poll
what kinda gas do you put in your C?
03-15-2002, 10:49 PM
#26
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C230 Kompressor Sports Sedan
i heard about the fuel setting for
performance and economy setting. how does this go? how can i change? or only dealer could do this?
thanx guys
performance and economy setting. how does this go? how can i change? or only dealer could do this?
thanx guys
03-16-2002, 01:25 AM
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GL450, Sienna SE
Hey doesnt it say on the gas cap premium unleaded only? Anyways I pump 91 octane. The cheapest I saw was $1.49 some place in the valley. I forget. If not, I'm gonna mix up 100 octane racing gas with 91 so i get something in the middle. Last time i checked it was $4.95 for 100 octane.
03-16-2002, 11:33 AM
#28
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Originally posted by toki999
i heard about the fuel setting for
performance and economy setting. how does this go? how can i change? or only dealer could do this?
thanx guys
i heard about the fuel setting for
performance and economy setting. how does this go? how can i change? or only dealer could do this?
thanx guys
yes, the dealer or a shop w/ the DAS software needs to do it.
07-13-2002, 05:09 PM
#29
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2002 C230 Coupe
100 Octane Gas
i pumped gas at 76 today and i saw there was a pump labeled 100 Racing Gasoline 
does anybody see this and has any one ever used this before??
will it improve the performance of the car or what?
does anybody see this and has any one ever used this before??
will it improve the performance of the car or what?
07-13-2002, 05:23 PM
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'02 C230K Coupe
The octane rating on a gasoline is related to the "purity" of the gasoline. The higher the octane rating, the fewer the extra "filler" chemicals in the gasoline. Higher octane indicates that the fuel gives more power, but it's generally more expensive. The fact that the gas station carried 100-octane gasoline usually indicates that there is a racing course nearby. Back at home, there was a 76 station next to a race course that had 102-octane gas.
My understanding is that having higher-octane gas will not damage your engine like low-octane gas, but there IS an option on the car computer that is designed for higher-octane gas, but you'll need to go to your dealer for that.
My understanding is that having higher-octane gas will not damage your engine like low-octane gas, but there IS an option on the car computer that is designed for higher-octane gas, but you'll need to go to your dealer for that.
07-13-2002, 06:27 PM
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2002 C230k
Um, well, no. The octane rating simply shows how well the fuel resists detonation. In fact a higher octane gas may well have more additives than a lower octane.
Putting 100 octane gas in your car won't do a dang thing to help performance if you aren't having problems with 93 octane.
Also note that a "racing fuel" may have a different chemical make-up than pump gasoline and may well require different parameters to run well, as in the A/F ratio that works just great for "gasoline" may not work as well with 110 octane RickyRacerRocket fuel...
Putting 100 octane gas in your car won't do a dang thing to help performance if you aren't having problems with 93 octane.
Also note that a "racing fuel" may have a different chemical make-up than pump gasoline and may well require different parameters to run well, as in the A/F ratio that works just great for "gasoline" may not work as well with 110 octane RickyRacerRocket fuel...
07-13-2002, 06:50 PM
#32
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MB coupe.
Higher octane gas has additives to make it burn slower, to prevent pre-ignition and detonation.
Modern cars may run slightly better on higher octane, as the ECU may detect detonation and roll back ignition timing without the higher octane.
Run what the manual suggests and don't waste your money thinking you will get better performance with higher octane fuels.
I have to run 94 octane in my '68 Firebird 400 convertible. It is hard to find, and expensive.
See ya, Smoky
Modern cars may run slightly better on higher octane, as the ECU may detect detonation and roll back ignition timing without the higher octane.
Run what the manual suggests and don't waste your money thinking you will get better performance with higher octane fuels.
I have to run 94 octane in my '68 Firebird 400 convertible. It is hard to find, and expensive.
See ya, Smoky
07-13-2002, 08:50 PM
#33
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Originally posted by Spyke
Um, well, no. The octane rating simply shows how well the fuel resists detonation. In fact a higher octane gas may well have more additives than a lower octane.
Um, well, no. The octane rating simply shows how well the fuel resists detonation. In fact a higher octane gas may well have more additives than a lower octane.
07-14-2002, 12:43 AM
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2002 C230k
Originally posted by Smoky
Higher octane gas has additives to make it burn slower, to prevent pre-ignition and detonation.
Higher octane gas has additives to make it burn slower, to prevent pre-ignition and detonation.
Higher octane gas can resist high temps and pressures longer than lower octane gas before it detonates. A fast flame speed is actually GOOD in that it burns more fuel before it has a chance to detonate.
What does "swirl" do in the intake charge? Makes the mixture burn faster. What do dual plugs do in a large bore cylinder? Make the mixture burn faster. Why would either of these be used if in fact making the mixture burn slower was a desired effect? Note that neither of these things change the speed of the flame front itself... so maybe a better way to state the question would be, why introduce mechanisms to burn the mixture faster and then make the gas itself burn slower???
07-15-2002, 03:30 AM
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'08 BMW e92 335i
i've tried it
i normally run chevron 91, but i tried 100 oct from 76. 2/3 tank and it felt as though the car was a lil more responsive not lightning fast but it had a lil more push at the lights.
07-15-2002, 09:48 AM
#37
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Originally posted by Spyke
Higher octane gasoline does not control detonation by burning slower. In fact, making the gas burn slower would make detonation WORSE.
Higher octane gas can resist high temps and pressures longer than lower octane gas before it detonates. A fast flame speed is actually GOOD in that it burns more fuel before it has a chance to detonate.
What does "swirl" do in the intake charge? Makes the mixture burn faster. What do dual plugs do in a large bore cylinder? Make the mixture burn faster. Why would either of these be used if in fact making the mixture burn slower was a desired effect? Note that neither of these things change the speed of the flame front itself... so maybe a better way to state the question would be, why introduce mechanisms to burn the mixture faster and then make the gas itself burn slower???
Higher octane gasoline does not control detonation by burning slower. In fact, making the gas burn slower would make detonation WORSE.
Higher octane gas can resist high temps and pressures longer than lower octane gas before it detonates. A fast flame speed is actually GOOD in that it burns more fuel before it has a chance to detonate.
What does "swirl" do in the intake charge? Makes the mixture burn faster. What do dual plugs do in a large bore cylinder? Make the mixture burn faster. Why would either of these be used if in fact making the mixture burn slower was a desired effect? Note that neither of these things change the speed of the flame front itself... so maybe a better way to state the question would be, why introduce mechanisms to burn the mixture faster and then make the gas itself burn slower???
I think you're explanation may be a little off. You are right that lower octane gas detonates earlier, but that is not usually a good thing. In a high compression engine, you need to use a sufficiently high octane gas so that the explosion occurs at (approximately) top dead center. If it happens early, you get a explosion on the pistons upstroke and it does not feel good-- usually presents as knocking. And it is bad for your engine.
Also, burning fast or slow is a misnomer. The rate of the explosion should be the same. It is just a matter of when it happens in the cycle.
Someone feel free to add details, etc. It has been a while since I studied this in engineering school.
07-15-2002, 09:50 AM
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Also, dual plugs are supposed to give a more complete detonation of the fuel-- not a change in timing or rate. A pretty significant amount of energy is wasted in fuel that does not burn completely. It is also bad for the environment. I believe it also results in build-up in your engine...
07-15-2002, 01:13 PM
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M3
Originally posted by kompress
Also, dual plugs are supposed to give a more complete detonation of the fuel-- not a change in timing or rate.
Also, dual plugs are supposed to give a more complete detonation of the fuel-- not a change in timing or rate.
What you are saying is that dual plugs causes a complete UNCONTROLLED Explosion of the gasoline. This implies that the engine would blow up with dual plugs (according to what you said).
WRONG WRONG WRONG.
07-15-2002, 01:18 PM
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2002 C230k
Originally posted by kompress
Also, dual plugs are supposed to give a more complete detonation of the fuel-- not a change in timing or rate.
Also, dual plugs are supposed to give a more complete detonation of the fuel-- not a change in timing or rate.
Detonation (knock) can and often does occur after TDC. Note that pre-ignition is NOT the same as detonation. Pre-ignition may lead to detonation, and detonation has been refered to as auto-ignition, but pre-ignition does not mean the same thing as detonation, at least not in any of the technical sources I've seen.
Dual plugs do give a more complete burn of the fuel... in a shorter amount of time. That's the point. They shorten the path the flame front has to travel to completely burn the fuel. This is related to why large bore cylinders are more likely to detonate than smaller bore cylinders.
07-15-2002, 01:29 PM
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2002 C230k
Originally posted by kompress
...You are right that lower octane gas detonates earlier, but that is not usually a good thing. In a high compression engine, you need to use a sufficiently high octane gas so that the explosion occurs at (approximately) top dead center. If it happens early, you get a explosion on the pistons upstroke and it does not feel good-- usually presents as knocking. And it is bad for your engine.
Detonation is virtually NEVER a good thing. Explosions in gasoline engines are virtually never a good thing. The ignition of the mixture is NOT controlled by the octane rating of the gas. It's controlled entirely by the ignition timing if everything's set up correctly. See my reply above regarding when knock can occur.
As for ignition before TDC, modern day cylinder designs are igniting the mixture closer to TDC, but using Harley as an example, some engines ignite the mixture up to 45 degrees BTD. Again, no explosions involved, Key point: Normal combustion is NOT an explosion.
Also, burning fast or slow is a misnomer. The rate of the explosion should be the same. It is just a matter of when it happens in the cycle.
The rate of combustion IS virtually the same between all grades of pump gas, true. In fact that was my original point. But the rate of combustion is not the same as the time it takes to burn the mixture. Intake designs and dual plugs certainly DO effect the time it takes for a complete burn. And again, the time it happens is not a function of the mixture assuming normal operation.
Someone feel free to add details, etc. It has been a while since I studied this in engineering school.
...You are right that lower octane gas detonates earlier, but that is not usually a good thing. In a high compression engine, you need to use a sufficiently high octane gas so that the explosion occurs at (approximately) top dead center. If it happens early, you get a explosion on the pistons upstroke and it does not feel good-- usually presents as knocking. And it is bad for your engine.
Detonation is virtually NEVER a good thing. Explosions in gasoline engines are virtually never a good thing. The ignition of the mixture is NOT controlled by the octane rating of the gas. It's controlled entirely by the ignition timing if everything's set up correctly. See my reply above regarding when knock can occur.
As for ignition before TDC, modern day cylinder designs are igniting the mixture closer to TDC, but using Harley as an example, some engines ignite the mixture up to 45 degrees BTD. Again, no explosions involved, Key point: Normal combustion is NOT an explosion.
Also, burning fast or slow is a misnomer. The rate of the explosion should be the same. It is just a matter of when it happens in the cycle.
The rate of combustion IS virtually the same between all grades of pump gas, true. In fact that was my original point. But the rate of combustion is not the same as the time it takes to burn the mixture. Intake designs and dual plugs certainly DO effect the time it takes for a complete burn. And again, the time it happens is not a function of the mixture assuming normal operation.
Someone feel free to add details, etc. It has been a while since I studied this in engineering school.
07-15-2002, 02:10 PM
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Spyke, nice reply. We always used the terms combustion, explosion and detonation interchangeably-- especially in lay environments. Please excuse me. Good thing I left Detroit when I did! 
I can't respond to your comments about shock waves and knocking without going back to the books. That is contrary to what I understood-- not to say it isn't right. I thought pre-ignition caused knocking and usually occured on the upstroke right before TDC (BTD?), and could be remedied by using a higher octane.
Also I always understood that the intake and spark set-up affected your 'completeness' of combustion rather than a rate.
KJ-TypeR, your message didn't really add anything to our collective understanding of what's going on under the hood. Maybe providing a little more explanation would help us more than :
'WRONG WRONG WRONG.'
But hey, that's one way to go...
I can't respond to your comments about shock waves and knocking without going back to the books. That is contrary to what I understood-- not to say it isn't right. I thought pre-ignition caused knocking and usually occured on the upstroke right before TDC (BTD?), and could be remedied by using a higher octane.
Also I always understood that the intake and spark set-up affected your 'completeness' of combustion rather than a rate.
KJ-TypeR, your message didn't really add anything to our collective understanding of what's going on under the hood. Maybe providing a little more explanation would help us more than :
'WRONG WRONG WRONG.'
But hey, that's one way to go...
07-15-2002, 02:17 PM
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M3
Originally posted by kompress
KJ-TypeR, your message didn't really add anything to our collective understanding of what's going on under the hood. Maybe providing a little more explanation would help us more than :
'WRONG WRONG WRONG.'
But hey, that's one way to go...
KJ-TypeR, your message didn't really add anything to our collective understanding of what's going on under the hood. Maybe providing a little more explanation would help us more than :
'WRONG WRONG WRONG.'
But hey, that's one way to go...
I'd rather say nothing, than run around saying "Hey guys, Mercedes is owned by Kia!!!".
07-15-2002, 02:42 PM
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Originally posted by KJ-TypeR
At least I'm not spreading grossly inaccurate information.
I'd rather say nothing, than run around saying "Hey guys, Mercedes is owned by Kia!!!".
At least I'm not spreading grossly inaccurate information.
I'd rather say nothing, than run around saying "Hey guys, Mercedes is owned by Kia!!!".
And what I was subtly trying to tell you is that I am part of groups like this because I like my toys, and like to appreciate them with others who do too. Putting people down with little good reason seems pretty asinine.
07-15-2002, 03:02 PM
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M3
Originally posted by kompress
Grossly inaccurate! Ha ha ha. Let's not get melodramatic here. Spyke pointed out that I should have used 'combustion' instead of 'detonation.'
Grossly inaccurate! Ha ha ha. Let's not get melodramatic here. Spyke pointed out that I should have used 'combustion' instead of 'detonation.'
Think about it this way.
Combustion is GOOD, and it's what makes a car move.
Detonation is BAD, and it's what blows your engine.
A good anology would be:
Skydiving is GOOD, because you survive due to having a parachute.
Jumping off a building is BAD, because you DIE when you hit the ground.
The bottom line is, one scenario is the IDEAL situation, whereas the other scenario is the WORST situation. By using the wrong word, the whole meaning of your sentence is affected.
It'd be like saying "I drive a Kia S500". Only the name "Kia" was misused, but it totally changes the meaning of what was written.
07-15-2002, 03:07 PM
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C230 Sports Coupe
just put in the highest octane you can get and leave it at that. Higher octane is better enough said!
07-15-2002, 03:16 PM
#49
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avlis - Sort of. Higher octane should COMBUST at a higher temperature and pressure than lower octane fuel. Come on boys, start flaming me-- pun intended...
KJ-TypeR - In a technical sense, you are correct. And my comment to you was that it would have been a whole lot more helpful and classier to say just that rather than what you chose to post.
But the reason why my choice of terms is more lax is because explaining the process in terms or mini-explosions is a lot more understandable to non-technical people who want to understand than combustion. So while it is not technically accurate (and I won't make that mistake again), it always seemed more polite to me to try to include folks in explanations rather than being too acronym- and lingo-heavy-- which is a pet-peeve of mine.
KJ-TypeR - In a technical sense, you are correct. And my comment to you was that it would have been a whole lot more helpful and classier to say just that rather than what you chose to post.
But the reason why my choice of terms is more lax is because explaining the process in terms or mini-explosions is a lot more understandable to non-technical people who want to understand than combustion. So while it is not technically accurate (and I won't make that mistake again), it always seemed more polite to me to try to include folks in explanations rather than being too acronym- and lingo-heavy-- which is a pet-peeve of mine.
07-15-2002, 04:29 PM
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2002 C230k
Originally posted by kompress
avlis - Sort of. Higher octane should COMBUST at a higher temperature and pressure than lower octane fuel. Come on boys, start flaming me-- pun intended...
But the reason why my choice of terms is more lax is because explaining the process in terms or mini-explosions is a lot more understandable to non-technical people who want to understand than combustion. So while it is not technically accurate (and I won't make that mistake again), it always seemed more polite to me to try to include folks in explanations rather than being too acronym- and lingo-heavy-- which is a pet-peeve of mine.
avlis - Sort of. Higher octane should COMBUST at a higher temperature and pressure than lower octane fuel. Come on boys, start flaming me-- pun intended...
But the reason why my choice of terms is more lax is because explaining the process in terms or mini-explosions is a lot more understandable to non-technical people who want to understand than combustion. So while it is not technically accurate (and I won't make that mistake again), it always seemed more polite to me to try to include folks in explanations rather than being too acronym- and lingo-heavy-- which is a pet-peeve of mine.
Forgive me my last attempt at describing it...
If you expose the air/fuel mixture to a given high temp and pressure (like inside the combustion chamber), there is a certain delay period before the mixture will auto-ignite/detonate/explode. That is, if I take the mixture and raise it's temp and pressure to what it sees inside the combustion chamber, after a certain amount of time it will auto-ignite*(detonate, explode). The trick is to burn the mixture in that short amount of time, the delay period, before it has a chance to explode.
A higher octane gas simply gives you a longer delay period for the same temp/conditions. That's it. 93 octane can withstand high temps and pressures longer than 89 octane before it goes "BANG".
While I agree with Kompress that simpler terms are preferred, the problem comes when someone wants to know a technical detail; then a subtle difference in terms can become important.
To understand knock, and therefore octane rating, you have to understand that when the mixture ignites it takes some time for it to burn. During this time nasty things can happen to the unburned portion of the mixture; with higher octane gas it takes longer for them to occur.
I'll shut up now as I see many of you yawning as you search for the scroll bar...
*Note this is not the same as pre-ignite. Pre-ignition occurs when a hot spot in the cylinder ignites the mixture before the plug fires. Auto-ignition can and will occur after the plug has fired!
Last edited by Spyke; 07-15-2002 at 04:32 PM.
