Fuel Octane Questions
11-19-2012, 03:03 PM
#1
Fuel Octane Questions
I've been using 87 octane in my car without any issues whatsoever. It's always ran great and I have never experienced any knocking. Now I've been reading many postings on this forum that discuss this very issue. As I understand it, the knock sensor will sense knock from low octane fuel causing the timing to be retarded which will in turn reduce performance and fuel efficiency. I also understand that all of this should go unnoticed to the driver as the reduction is limited.
I decided to run a test.
I set my cruise control at 72 mph on a flat straight stretch of I-70 and monitored my ignition timing advance with both 87 and 93 octane fuel over the period of a couple weeks. I found no discernible difference in the ignition timing. The ignition timing was almost steady at 34-35 degrees btdc irregardless of octane. Fuel usage calculations are still pending.
Any thoughts? Is there something I'm missing or need schooled on? Am I taking this too far?
I decided to run a test.
I set my cruise control at 72 mph on a flat straight stretch of I-70 and monitored my ignition timing advance with both 87 and 93 octane fuel over the period of a couple weeks. I found no discernible difference in the ignition timing. The ignition timing was almost steady at 34-35 degrees btdc irregardless of octane. Fuel usage calculations are still pending.
Any thoughts? Is there something I'm missing or need schooled on? Am I taking this too far?
11-19-2012, 04:01 PM
#2
No not missing something, just misunderstanding. Different engines are built different ways for different compression and valve/ignition timing. A higher compression engine is built for a higher octane to resist detonation and knock while an engine built of lower compression can use a lower octane and not have to worry about knock. When you use a lower octane rating in an engine meant for a higher octane fuel, it is basically making the knock sensor and the ECU( in our specific engine) continuously adjust the timing. So instead of the timing actually changing, your ECU just adjusts for the lower octane rating and thus performance decreases a little bit. The timing would not actually change by much or you would be driving a different car everyday and thats what manufacturers aim to eliminate via different systems. I am no expert but this is how I understand it to work so you will never read a big change in timing because that is the point of the knock sensor and ECU IE reading operating parameters and adjusting for them.
Last edited by ShocknAwe; 11-19-2012 at 04:04 PM.
11-19-2012, 04:06 PM
#3
Senior Member
Join Date: Sep 2010
Location: Jacksonville, FL
Posts: 10,349
Timing becomes more advanced when you're at full throttle going higher up in the rpm's. You were traveling at a set speed with little load on the engine, so there was no need for the car's computer to advance the timing any more than it needed, regardless of the octane fuel. That's why fuel doors on 5th gens say "Premium fuel recommended for maximum performance" and you were not driving in a performance situation.
11-19-2012, 10:49 PM
#6
I don't think we would see big hp numbers between octane on a stock car, rather results more related to throttle responsivity and fuel economy. Want to see/feel a big difference? Fill your tank up with 93 ethanal free.
11-20-2012, 10:23 AM
#8
You don't need anything higher than 87 octane on a stock 2002/2003 Maxima.
Too much timing with too low an octane fuel can cause knock, along with a bunch of other variables. The stock computers timing is Mapped for 87 Octane fuel, so you're fine. The primary reasons to change octane is if you're changing the timing via. a different Tune, or if you're supercharged/turbocharged.
Too much timing with too low an octane fuel can cause knock, along with a bunch of other variables. The stock computers timing is Mapped for 87 Octane fuel, so you're fine. The primary reasons to change octane is if you're changing the timing via. a different Tune, or if you're supercharged/turbocharged.
11-20-2012, 12:23 PM
#9
WHAT?! I prefer to drive Monique after she gets her fill of steak and potatoes (93 octane) rather than after cramming her full of rice cakes (87). But, that's just me. Mmmmmmm! Monique likes her some steak and potatoes!
11-20-2012, 02:01 PM
#11
11-20-2012, 02:21 PM
#13
http://www.rockettbrand.com/techsupp...ationships.pdf
Pulled from above:
Octane Number: The octane number of a gasoline has little to do with how fast it burns or how much
power the engine will make. Octane number is the resistance to detonation. If the octane number is high
enough to prevent detonation, there is no need to use a higher octane gasoline since the engine will not make
any additional power. Octane number is not related to flame (burn) speed either. Variations in octane quality
are independent of flame speed. There are some high octane gasolines in the marketplace with fast flame
speeds and some with slow flame speeds. It depends on how they are put together. At Rockett BrandTM, we like
fast flame speeds because we know that a properly tuned engine will make more power on this type of gasoline
than one that has a slower flame speed.
power the engine will make. Octane number is the resistance to detonation. If the octane number is high
enough to prevent detonation, there is no need to use a higher octane gasoline since the engine will not make
any additional power. Octane number is not related to flame (burn) speed either. Variations in octane quality
are independent of flame speed. There are some high octane gasolines in the marketplace with fast flame
speeds and some with slow flame speeds. It depends on how they are put together. At Rockett BrandTM, we like
fast flame speeds because we know that a properly tuned engine will make more power on this type of gasoline
than one that has a slower flame speed.
http://motorcycleriderz.motionsforum...t-a-fuel-burns
And a Very interesting fact about "Octane" itself and where it comes from:
The name "octane" comes from the following fact: When you take crude oil and "crack" it in a refinery, you end up getting hydrocarbon chains of different lengths. These different chain lengths can then be separated from each other and blended to form different fuels. For example, you may have heard of methane, propane and butane. All three of them are hydrocarbons. Methane has just a single carbon atom. Propane has three carbon atoms chained together. Butane has four carbon atoms chained together. Pentane has five, hexane has six, heptane has seven and octane has eight carbons chained together.
It turns out that heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot and nothing happens. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.
It turns out that heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot and nothing happens. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.
11-20-2012, 02:34 PM
#14
A simple way to put it:
Lower octane fuel (87) burns easier.
Higher (91) Octane fuel is harder to burn.
Because 91 is harder to burn, it won't detonate as easily in Higher compression engines. However, if the engine doesn't knock or retard timing when using 87, using 91 WILL NOT INCREASE YOUR PERFORMANCE. In fact, it's quite possible it can REDUCE performance on cars that aren't designed for it because it's harder to ignite the mixture.
Another loose way to put it:
Engines designed for 91 (high octane) fuel generally have higher compression, and more advanced timing. It's not the OCTANE that gives you the power, it's the Higher compression and Advanced timing.
All the Octane does is keep it from detonating at this higher compression and higher temperature.
Lower octane fuel (87) burns easier.
Higher (91) Octane fuel is harder to burn.
Because 91 is harder to burn, it won't detonate as easily in Higher compression engines. However, if the engine doesn't knock or retard timing when using 87, using 91 WILL NOT INCREASE YOUR PERFORMANCE. In fact, it's quite possible it can REDUCE performance on cars that aren't designed for it because it's harder to ignite the mixture.
Another loose way to put it:
Engines designed for 91 (high octane) fuel generally have higher compression, and more advanced timing. It's not the OCTANE that gives you the power, it's the Higher compression and Advanced timing.
All the Octane does is keep it from detonating at this higher compression and higher temperature.
11-20-2012, 02:59 PM
#16
Timing becomes more advanced when you're at full throttle going higher up in the rpm's. You were traveling at a set speed with little load on the engine, so there was no need for the car's computer to advance the timing any more than it needed, regardless of the octane fuel. That's why fuel doors on 5th gens say "Premium fuel recommended for maximum performance" and you were not driving in a performance situation.
Drive like Ms Daisy? use 87
Drive it like you stole it? 93 octane for MAXIMA performance.
11-20-2012, 08:00 PM
#18
Senior Member
Join Date: Sep 2010
Location: Jacksonville, FL
Posts: 10,349
11-20-2012, 08:20 PM
#20
I also use the . It's small enough to fit almost flush with the kick panel under the dash. My old one used to hit me in the knee all the time. I just leave this one in place.
11-20-2012, 08:24 PM
#22
Here is the link to the myths of unleaded gasoline:
http://www.pontiacstreetperformance....Mythsgas1.html
I live in higher altitude in Colorado and have been running 87 to 91 octane. I have yet to know the difference in performance when driving hard. Does that mean there isn't a difference? NO! Just not noticeable by me.
I hope this helps some of your questions.
http://www.pontiacstreetperformance....Mythsgas1.html
I live in higher altitude in Colorado and have been running 87 to 91 octane. I have yet to know the difference in performance when driving hard. Does that mean there isn't a difference? NO! Just not noticeable by me.
I hope this helps some of your questions.
11-21-2012, 04:27 AM
#24
n/p dude!
lol'd at the leaded gas link? Wtf, am I missing something on this?
11-21-2012, 07:39 AM
#25
not to be a smart a** but you do understand that the equipment that is used to monitor engine data costs thousands of dollars and at this point you are judging you results based on a $15 Bluetooth plug in OBD2 reader and a $4.99 app on your smart phone??? Give me one reason or an example of why this data is accurate??? 
Don't get me wrong I do have the same Bluetooth OBD2 reader but I use it only to pull codes stored in the ECU and nothing else.
Don't get me wrong I do have the same Bluetooth OBD2 reader but I use it only to pull codes stored in the ECU and nothing else.
11-21-2012, 08:58 AM
#27
not to be a smart a** but you do understand that the equipment that is used to monitor engine data costs thousands of dollars and at this point you are judging you results based on a $15 Bluetooth plug in OBD2 reader and a $4.99 app on your smart phone??? Give me one reason or an example of why this data is accurate???
Don't get me wrong I do have the same Bluetooth OBD2 reader but I use it only to pull codes stored in the ECU and nothing else.
Don't get me wrong I do have the same Bluetooth OBD2 reader but I use it only to pull codes stored in the ECU and nothing else.
OBD2 is fairly old, reliable, and simple technology. The only places where you need thousands of dollars of equipment is to use OEM proprietary features that don't follow the OBD2 standard. My dad has a $600 dollar scanner that doesn't do much my $15 bluetooth adapter can't do. It's just not rocket science anymore.
Besides, you've forgotten that this $15 dollar adapter and $5 software is just the backend on a $500 computer (which is all cell phones are anymore). I may not trust it to be perfectly accurate but I feel the limitations are with the OBD2 protocol, not my cheap *** equipment.
11-21-2012, 09:19 AM
#28
^I would have to agree. They are useless for accurate diagnostics though, because they simply don't read the information fast enough. They can give you half decent guidlines, but you could NEVER diagnose a MAF sensor or anything like that with one. Even fuel trims are a Wash to accurately check with them, too slow.
Then there's something wrong with your car.
Then there's something wrong with your car.
11-21-2012, 09:30 AM
#29
^I would have to agree. They are useless for accurate diagnostics though, because they simply don't read the information fast enough. They can give you half decent guidlines, but you could NEVER diagnose a MAF sensor or anything like that with one. Even fuel trims are a Wash to accurately check with them, too slow.
Was just doing some reading up on OBD3 and found some disturbing things...I hope that's not set in stone yet.
11-21-2012, 10:31 AM
#30
Code reading equipment costs hundreds of dollars!! What makes you think your $20 bluetooth setup is pulling accurate codes?!? /Sarcasm off
OBD2 is fairly old, reliable, and simple technology. The only places where you need thousands of dollars of equipment is to use OEM proprietary features that don't follow the OBD2 standard. My dad has a $600 dollar scanner that doesn't do much my $15 bluetooth adapter can't do. It's just not rocket science anymore.
Besides, you've forgotten that this $15 dollar adapter and $5 software is just the backend on a $500 computer (which is all cell phones are anymore). I may not trust it to be perfectly accurate but I feel the limitations are with the OBD2 protocol, not my cheap *** equipment.
OBD2 is fairly old, reliable, and simple technology. The only places where you need thousands of dollars of equipment is to use OEM proprietary features that don't follow the OBD2 standard. My dad has a $600 dollar scanner that doesn't do much my $15 bluetooth adapter can't do. It's just not rocket science anymore.
Besides, you've forgotten that this $15 dollar adapter and $5 software is just the backend on a $500 computer (which is all cell phones are anymore). I may not trust it to be perfectly accurate but I feel the limitations are with the OBD2 protocol, not my cheap *** equipment.
11-21-2012, 04:14 PM
#31
Senior Member
Join Date: Sep 2010
Location: Jacksonville, FL
Posts: 10,349
11-21-2012, 06:26 PM
#32
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