91 octane with a stock LT1
05-21-2003, 05:26 AM
#1
Registered User
Thread Starter
Join Date: Sep 1998
Location: Oakville, Ontario
Posts: 679
91 octane with a stock LT1
Up here our Esso stations have now gone from 92 octane to 91 octane, so the only way to get higher than 91 now is to get Sunoco gas, which uses ethanol and kills my MPG.
So what I'd like to know is how much, if any, spark retard can I expect to see when running 91 octane in my totally stock LT1 in the hot summertime? It occasionally gets up to 95F here, but a typical summer day is about 80F here.
So what I'd like to know is how much, if any, spark retard can I expect to see when running 91 octane in my totally stock LT1 in the hot summertime? It occasionally gets up to 95F here, but a typical summer day is about 80F here.
05-21-2003, 09:26 AM
#4
Administrator
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,677
What is the elevation where you live? The higher it is, the less octane you need.
The only way you will ever know if you are losing performance is to monitor knock retard with a scanner.
The only way you will ever know if you are losing performance is to monitor knock retard with a scanner.
05-21-2003, 09:33 AM
#5
Registered User
Thread Starter
Join Date: Sep 1998
Location: Oakville, Ontario
Posts: 679
The elevation here is only about 6 or 700ft above sea level.
I have used Datamaster in the past to check knock retard, and with 92 octane in 50 degree weather I was still getting 3-4 degrees of retard in 3rd gear, although since then I've done a lot of stuff that would help in that regard (combustion chamber cleaner, new 02 sensors, fixed a vacuum leak, finally replaced the one original plug I had, new fuel filter)
I have used Datamaster in the past to check knock retard, and with 92 octane in 50 degree weather I was still getting 3-4 degrees of retard in 3rd gear, although since then I've done a lot of stuff that would help in that regard (combustion chamber cleaner, new 02 sensors, fixed a vacuum leak, finally replaced the one original plug I had, new fuel filter)
05-21-2003, 10:30 AM
#8
Registered User
Join Date: Mar 2003
Location: PA
Posts: 1,574
Originally posted by treyZ28
91 octane is GM's minimun requirement for the LT1.
I wouldn't expect to see any.. i dont think i saw any on 89...
91 octane is GM's minimun requirement for the LT1.
I wouldn't expect to see any.. i dont think i saw any on 89...
05-21-2003, 12:15 PM
#9
Registered User
Join Date: Sep 2000
Location: Billings, MT, U.S.A
Posts: 138
Originally posted by chasmanz28
...but first, lets explain what octane really is. Essentially, the higher the octane of gas, the more amount of oxygen it takes to burn the fuel. The more oxygen used to burn the gas means the quicker and cleaner it will burn. In larger, performance minded engines, you need to have a clean burning, fast fuel. Engines like the LT1 have a computer, which is set to provide as much oxygen necessary to burn the fuel, if you run too low of an octane gas in an engine, it is not putting more oxygen into the engine than necessary, so it will adjust the timing of the engine so it doesn't overdo it. Although this won't harm the engine, the fuel to air ratio will be less than optimal, and this will decrease your performance. So, running anything other than premium gas (which is usually between 92 and 94 octane depending on where you go) can potentially make your car run less than what it could. To be safe, the manufacturer recommends that you do not run anything lower than premium gas in the V8s.
...but first, lets explain what octane really is. Essentially, the higher the octane of gas, the more amount of oxygen it takes to burn the fuel. The more oxygen used to burn the gas means the quicker and cleaner it will burn. In larger, performance minded engines, you need to have a clean burning, fast fuel. Engines like the LT1 have a computer, which is set to provide as much oxygen necessary to burn the fuel, if you run too low of an octane gas in an engine, it is not putting more oxygen into the engine than necessary, so it will adjust the timing of the engine so it doesn't overdo it. Although this won't harm the engine, the fuel to air ratio will be less than optimal, and this will decrease your performance. So, running anything other than premium gas (which is usually between 92 and 94 octane depending on where you go) can potentially make your car run less than what it could. To be safe, the manufacturer recommends that you do not run anything lower than premium gas in the V8s.
Octane as generally accepted, is simply the fuel's ability to resist detonation. Beyond that there is very little need to go with higher octane (why on God's green earth run premium in that Honda Accord type thing). Higher altitude areas (mine is 3750') are offered lower octane fuels (highest here is 91) due to the lower density of air entering the engine, thus softer combustion and lower cyl pressures.
Anyway, neither here nor there I guess. A good explanation of octane and where exactly it comes from is located here.
Octane explained
Fun reading if slightly scientifically minded.
IMO, if running higher compression heads / pistons (I'm actually a bit lower here), or running FI (me, thus why I desire higher octane than the 91 I'm offered *read.. Home blends*) or juice then you require higher octane than what is generally offered. If not then the premium offered in your area is probably sufficient.
{edited to make linky link}
Last edited by wile2k; 05-21-2003 at 12:17 PM.
05-21-2003, 03:34 PM
#10
Administrator
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,677
Originally posted by chasmanz28
Well, once again, this is up to you, but first, lets explain what octane really is. Essentially, the higher the octane of gas, the more amount of oxygen it takes to burn the fuel. The more oxygen used to burn the gas means the quicker and cleaner it will burn. In larger, performance minded engines, you need to have a clean burning, fast fuel. Engines like the LT1 have a computer, which is set to provide as much oxygen necessary to burn the fuel, if you run too low of an octane gas in an engine, it is not putting more oxygen into the engine than necessary, so it will adjust the timing of the engine so it doesn't overdo it. Although this won't harm the engine, the fuel to air ratio will be less than optimal, and this will decrease your performance. So, running anything other than premium gas (which is usually between 92 and 94 octane depending on where you go) can potentially make your car run less than what it could. To be safe, the manufacturer recommends that you do not run anything lower than premium gas in the V8s.
Well, once again, this is up to you, but first, lets explain what octane really is. Essentially, the higher the octane of gas, the more amount of oxygen it takes to burn the fuel. The more oxygen used to burn the gas means the quicker and cleaner it will burn. In larger, performance minded engines, you need to have a clean burning, fast fuel. Engines like the LT1 have a computer, which is set to provide as much oxygen necessary to burn the fuel, if you run too low of an octane gas in an engine, it is not putting more oxygen into the engine than necessary, so it will adjust the timing of the engine so it doesn't overdo it. Although this won't harm the engine, the fuel to air ratio will be less than optimal, and this will decrease your performance. So, running anything other than premium gas (which is usually between 92 and 94 octane depending on where you go) can potentially make your car run less than what it could. To be safe, the manufacturer recommends that you do not run anything lower than premium gas in the V8s.
If you have a documented reference to your statement, I'd like to see it. In the meantime, you might want to review Section 6 of the GASOLINE FAQ
05-21-2003, 03:58 PM
#11
Banned
Join Date: Aug 2001
Location: looking for a flow bench so Brook and I can race
Posts: 3,505
Originally posted by Injuneer
In my 40 years of engineering, inculding significant time with a major oil company, I have never heard anything like what you just described. In fact, it can be easilly demonstrated that "octane" had NOTHING whatsoever to do with energy content of the fuel, burn speed of the fuel, A/F stoichiometry, etc. Octane is solely a measure of the fuel's resistance to forming "end gasses" that will auto-ignite under the temperature and pressure of the flame front created by the spark ignition.
If you have a documented reference to your statement, I'd like to see it. In the meantime, you might want to review Section 6 of the GASOLINE FAQ
In my 40 years of engineering, inculding significant time with a major oil company, I have never heard anything like what you just described. In fact, it can be easilly demonstrated that "octane" had NOTHING whatsoever to do with energy content of the fuel, burn speed of the fuel, A/F stoichiometry, etc. Octane is solely a measure of the fuel's resistance to forming "end gasses" that will auto-ignite under the temperature and pressure of the flame front created by the spark ignition.
If you have a documented reference to your statement, I'd like to see it. In the meantime, you might want to review Section 6 of the GASOLINE FAQ
05-21-2003, 04:53 PM
#12
Registered User
Join Date: Apr 2000
Location: Tulsa
Posts: 1,208
Originally posted by Injuneer
In my 40 years of engineering, inculding significant time with a major oil company, I have never heard anything like what you just described. In fact, it can be easilly demonstrated that "octane" had NOTHING whatsoever to do with energy content of the fuel, burn speed of the fuel, A/F stoichiometry, etc. Octane is solely a measure of the fuel's resistance to forming "end gasses" that will auto-ignite under the temperature and pressure of the flame front created by the spark ignition.
If you have a documented reference to your statement, I'd like to see it. In the meantime, you might want to review Section 6 of the GASOLINE FAQ
In my 40 years of engineering, inculding significant time with a major oil company, I have never heard anything like what you just described. In fact, it can be easilly demonstrated that "octane" had NOTHING whatsoever to do with energy content of the fuel, burn speed of the fuel, A/F stoichiometry, etc. Octane is solely a measure of the fuel's resistance to forming "end gasses" that will auto-ignite under the temperature and pressure of the flame front created by the spark ignition.
If you have a documented reference to your statement, I'd like to see it. In the meantime, you might want to review Section 6 of the GASOLINE FAQ
05-21-2003, 09:22 PM
#13
Administrator
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,677
Originally posted by IrocManiac
From what I've read and a friend of mine who is a chem engineer told me is that what you said is correct about end gasses etc, however, I have read that it has to do with burn speed as well. My mechanic also told me this. The higher octane gas burns slightly slower and therefore more evenly over the pistons which is critical on high performance and bigger bore motors.
From what I've read and a friend of mine who is a chem engineer told me is that what you said is correct about end gasses etc, however, I have read that it has to do with burn speed as well. My mechanic also told me this. The higher octane gas burns slightly slower and therefore more evenly over the pistons which is critical on high performance and bigger bore motors.
From the reference posted above:
The antiknock ability is related to the "autoignition temperature" of the hydrocarbons. Antiknock ability is _not_ substantially related to:-
1. The energy content of fuel, this should be obvious, as oxygenates have lower energy contents, but high octanes.
2. The flame speed of the conventionally ignited mixture, this should be evident from the similarities of the two reference hydrocarbons. Although flame speed does play a minor part, there are many other factors that are far more important. ( such as compression ratio, stoichiometry,combustion chamber shape, chemical structure of the fuel, presence of antiknock additives, number and position of spark plugs, turbulence etc.)
Flame speed does not correlate with octane.
1. The energy content of fuel, this should be obvious, as oxygenates have lower energy contents, but high octanes.
2. The flame speed of the conventionally ignited mixture, this should be evident from the similarities of the two reference hydrocarbons. Although flame speed does play a minor part, there are many other factors that are far more important. ( such as compression ratio, stoichiometry,combustion chamber shape, chemical structure of the fuel, presence of antiknock additives, number and position of spark plugs, turbulence etc.)
Flame speed does not correlate with octane.
.Detonation destroys parts due to the extremely high pressures, and accompanying resonances as a result of the collision of the two flame fronts.
05-21-2003, 09:31 PM
#14
Banned
Join Date: Aug 2001
Location: looking for a flow bench so Brook and I can race
Posts: 3,505
Originally posted by IrocManiac
From what I've read and a friend of mine who is a chem engineer told me is that what you said is correct about end gasses etc, however, I have read that it has to do with burn speed as well. My mechanic also told me this. The higher octane gas burns slightly slower and therefore more evenly over the pistons which is critical on high performance and bigger bore motors. Running 87 octane gas can cause the piston rings for example in an LT1 to warp over time due to uneven burn. This is an even bigger problem on the 4.6 L ford motors. People run 87 octane and it will warp the rings (I've seen it first hand) when premium is run there isn't usually a problem or not nearly as bad.
From what I've read and a friend of mine who is a chem engineer told me is that what you said is correct about end gasses etc, however, I have read that it has to do with burn speed as well. My mechanic also told me this. The higher octane gas burns slightly slower and therefore more evenly over the pistons which is critical on high performance and bigger bore motors. Running 87 octane gas can cause the piston rings for example in an LT1 to warp over time due to uneven burn. This is an even bigger problem on the 4.6 L ford motors. People run 87 octane and it will warp the rings (I've seen it first hand) when premium is run there isn't usually a problem or not nearly as bad.
also the rule of averages tells you that this "lobsided flame
" will not "lean" to the same side every time.. And there is no "leverage" to "twist" the rings. I'm sure sliding up and down the cylinder wall will even everything out
also- good luck melting moly rings under normal conditions.
Christ, i'm only a freshman and i could figure out this is
Thread
Thread Starter
Forum
Replies
Last Post
dbusch22
Forced Induction
6
10-31-2016 11:09 AM
oldschool
Parts For Sale
16
02-09-2016 09:21 PM
Brandon Wittmer
General 1967-2002 F-Body Tech
3
12-03-2014 09:28 PM