View Full Version : 93 Octane & Oil Question
ablehunter
11-03-2006, 07:34 AM
The manual says I need to fill up with "premium" 91 octane; however, most of the stations i go to have 87 -89 -93....sometime they have all four 87 -89 -91 - 93. I have been filling up with 93. I assume that is wont do any harm; other than providing the good folks at exxon-moble with a few extra $'s is there any difference/benefit and/or harm in running on 93 instead of 91 ??? Second stupid question...i was told that i should have my "first oil change" done at or about 2500 miles, and ignore the dic. Is that true??
Thanks for all the help!!
treyster
11-03-2006, 08:15 AM
Theoretically, the more octane you have, the less timing the computer will pull out and the more power you will have. That works to a point and it is possible that too high octane (over 110?) will begin to hurt power. Octane slows down the burn rate of gasoline and if there is not enough cylinder pressure, i.e low compression, it will be counterproductive. I'm guessing with close to 11:1 in the LS2, ideally you would like to have close to 100 octane. Run the highest octane you can find at the pump. I have Sunoco 94 near me, so that's what I run. If you are towing, it's very important.
You can run 87, just keep your foot out of it and you'll never build enough cylinder pressure to create a problem.
rrmccabe
11-03-2006, 08:32 AM
Second stupid question...i was told that i should have my "first oil change" done at or about 2500 miles, and ignore the dic. Is that true??
Thanks for all the help!!
Regarding your second question. I like to change early (so yes ignore the DIC).
Never hurts and assembly contaminations can be removed on this first change. I think my first was at 1000.
Rich
Nukedog
11-03-2006, 09:53 AM
Theoretically, the more octane you have, the less timing the computer will pull out and the more power you will have. That works to a point and it is possible that too high octane (over 110?) will begin to hurt power. Octane slows down the burn rate of gasoline and if there is not enough cylinder pressure, i.e low compression, it will be counterproductive. I'm guessing with close to 11:1 in the LS2, ideally you would like to have close to 100 octane. Run the highest octane you can find at the pump. I have Sunoco 94 near me, so that's what I run. If you are towing, it's very important.
You can run 87, just keep your foot out of it and you'll never build enough cylinder pressure to create a problem.
This is all based on the knock sensors. If it doesn't knock at 89octane then the computer will knock pull timing...
The LS2 is 10.9:1 C/R and you are correct. Run the least amount of octane possible to make the most power without letting the motor knock or ping.
My motorcycle is 13.5:1 and i use 89 in it mixed with 93...
rrmccabe
11-03-2006, 10:03 AM
This is all based on the knock sensors. If it doesn't knock at 89octane then the computer will knock pull timing...
The LS2 is 10.9:1 C/R and you are correct. Run the least amount of octane possible to make the most power without letting the motor knock or ping.
My motorcycle is 13.5:1 and i use 89 in it mixed with 93...
Just keep in mind the knock is not always audible when the timing is being pulled. I have scan logs of my SS showing knock and timing being pulled at certain times I could not hear it. Sometimes it was very audible.
02redhawk
11-03-2006, 12:47 PM
Theoretically, the more octane you have, the less timing the computer will pull out and the more power you will have. That works to a point and it is possible that too high octane (over 110?) will begin to hurt power. Octane slows down the burn rate of gasoline and if there is not enough cylinder pressure, i.e low compression, it will be counterproductive. I'm guessing with close to 11:1 in the LS2, ideally you would like to have close to 100 octane.
No, this is incorrect. The LS2 & the timing tables were designed to provide the most power with premium pump fuel (ie, 91-93 octane), nothing more. Provided that you are getting no KR with 91 octane, then it is of no benefit whatsoever to run 93 octane. However, if you have even 1* of consistent KR with 91 octane, then your engine would slightly benefit from 92 or 93. Running anything more than what gives you 0* KR *will* begin to reduce power (just like Treyster stated above about slowing the burn rate).
Run the highest octane you can find at the pump. I have Sunoco 94 near me, so that's what I run.
If you have a datalogger, take some logs of your vehicle with Sunoco 94 (which is oxygenated), and then do a fillup of Amoco/Mobil 93 (non-oxygenated). You might be surprised with what you find.
torker
11-03-2006, 12:55 PM
If you have a datalogger, take some logs of your vehicle with Sunoco 94 (which is oxygenated), and then do a fillup of Amoco/Mobil 93 (non-oxygenated). You might be surprised with what you find.[/quote]
Redhawk, do tell. Also how can I tell at the pump which I'm getting.? I just run 87 in my I6 but I have had it ping KR? on some 87 but not others.
Nukedog
11-03-2006, 01:00 PM
Just keep in mind the knock is not always audible when the timing is being pulled. I have scan logs of my SS showing knock and timing being pulled at certain times I could not hear it. Sometimes it was very audible.
That is what knock sensors are for...
Envoy Fan
11-03-2006, 01:12 PM
If you have a datalogger, take some logs of your vehicle with Sunoco 94 (which is oxygenated), and then do a fillup of Amoco/Mobil 93 (non-oxygenated). You might be surprised with what you find.
What did you find when you did the logs on the different fuels?
Nukedog
11-03-2006, 01:13 PM
That is what knock sensors are for...
If you have a datalogger, take some logs of your vehicle with Sunoco 94 (which is oxygenated), and then do a fillup of Amoco/Mobil 93 (non-oxygenated). You might be surprised with what you find.
Redhawk, do tell. Also how can I tell at the pump which I'm getting.? I just run 87 in my I6 but I have had it ping KR? on some 87 but not others.[/QUOTE]
Sunoco 94 is gonna make more rwhp due to the fact it is a MTBE fuel or "oxygenated" at 3.7% and with that being said it also could have a tenedency to run lean if the tune isn't correct for it.
Many states are slowly banning MTBE fuels from pumps...
torker
11-03-2006, 02:06 PM
Many states are slowly banning MTBE fuels from pumps...[/quote]
I have noticed this too. So, It should say on the pump if it contains mtbe?
Man, Buying fuel is such a crapshoot these days. Especially when traveling or even just doing a lotta miles in a large local area.
So can you all tell me wether running 91 for awhile and letting the puter relearn will make more power from my I6? It's over 10to1 I think. Should be able to gain some power?:undecided
Nukedog
11-03-2006, 02:58 PM
Not sure to be honest. I use 87 and 89 mostly in my 5.3 with a VERY heavy foot. i did in my 5.3 Silvy and it was same c/r as the TB and your I6...
treyster
11-03-2006, 03:24 PM
RedHawk
I put a 11.2:1 (true) comp. 455 in my '67 Riviera with a MSD7AL and it is right on the edge of detonation with 94 Sunoco. The combustion chamber is very compact, not like a BB Chevy. I need a little more octane than 94. I run about 34-36 degrees of total timing. Obviously, it's cast iron and not aluminum.
I don't know much about the tables the TBSS references, but if they are optimized for about 92 octane, isn't there potential power in having them optimized for 94 octane? Seems to me, based on my experience from my Riviera, that this kind of cylinder pressure needs more octane than 91 to have an ideal timing curve.
Anyone have any thoughts?
torker
11-03-2006, 03:31 PM
hmmm , I know in my old non computer 350, it is 10to1 and likes to run on 93 no less. Of course that is purely mechanical. I just wonder at what octane do our knock sensors start pulling timing. I know there is a ton of variables.
02redhawk
11-03-2006, 04:25 PM
Redhawk, do tell. Also how can I tell at the pump which I'm getting.? I just run 87 in my I6 but I have had it ping KR? on some 87 but not others.
94-oxygenated will have a greater tendency to knock over 93 non-oxygenated...and your STFT+LTFTs will start to increase (meaning the system is leaner and the PCM is adding fuel).
I've logged my past / current vehicles (modded GTZ, Syclone, Firehawk, GP-GTP, etc), and always have had the same result. The car/truck runs better on 93 non-oxy.
BP/Amoco/Mobil are all non-Oxy. Sunoco, I won't touch the stuff.
torker
11-03-2006, 04:59 PM
Well I haven't seen Sunoco in this area. We have/had P-66 I think they got bought out. There is some BP, Shell, Conoco. And others but I'm not sure if one is better?? Plus we do have a couple Amoco still. They seem to be fading.