87 vs 93 Octane
Senior Member
Joined: 10-02-2005
Posts: 1,245
From: VA
Well JoeR, I am a senior controls engineer at GM Powertrain and I have designed and coded many engine controllers in my time and there certainty are octane sensors (don't think so? google it). If you have access to an instrument like the Dashhawk for example, you can view the octane sensor's output.
In the context of this discussion, volatility has everything to do with it and you described the meaning very well in the words that followed.
You did not reference what cal file you looked (nor did I) but I was simply offing an example, the example I used is from the IAT table for an LS2 engine.
So I'll ask you the same, where do you come up with this stuff?
In the context of this discussion, volatility has everything to do with it and you described the meaning very well in the words that followed.
You did not reference what cal file you looked (nor did I) but I was simply offing an example, the example I used is from the IAT table for an LS2 engine.
So I'll ask you the same, where do you come up with this stuff?
Again, there are NO "octane sensors" in any of our current HHRs. Only knock sensor. If you are so well connected, as you say, please provide me a Part No. for the one in my '06 HHR 2.4 LE5, as a friend who is a parts manager confirms that there is no such thing, nor is it a listed PID.
I have something much more sophisticated than the Dashhawk... HP Tuners and among the hundreds of PIDs, there is absolutely nothing related to octane. I can data log in detail about timing, knock retard, knock learn factor and much more related to this.
Volatility is all related to evaporation characteristics, not flame propogation rates.
Calibration tables regarding spark have nothing to do with the point that KR can be activated. The tables only relate IAT to spark as modifiers during normal operation, as they should.
Most of my experience is related to the LE5 2.4 E67 ECM and I will be more that glad to post screen shots of the actual tables related to any of this. Can you?
Senior Member
Joined: 03-27-2008
Posts: 471
From: Blue Springs Missouri
welp here is my 
JMHO
I am not a mechanic nor am i math major, or a scientist,
Here in Missouri Havent seen any of the so call 93 octane, but really havent looked for any,
I filled up with a couple of tanks of the 91 so i could see for myself in my situation if there would be any difference between the 91 and the 87 octane. I didnt see but a mile difference in the mpg, Performance I didnt noticed any noticable difference.
But i think different states has different qulifications or specs they require for their gas, and that does effect the mileage ones gets.
True there are even gas stations around that i wouldnt even use for my lawn mower, but i get my gas at a couple of places one guarantees there gas.
I have driven a couple of SS which in MY opion i didnt see much difference if any in the performance over my 2.4, although i do like the looks of the SS at this point wouldnt give mine up for one for now.
So in MY case 87 is just fine, not worth getting in a big up roar over which one to use...93,91,89,87, it got 87 in the first tank, and still gets 87 and it Runs Great.
JMHOI am not a mechanic nor am i math major, or a scientist,
Here in Missouri Havent seen any of the so call 93 octane, but really havent looked for any,
I filled up with a couple of tanks of the 91 so i could see for myself in my situation if there would be any difference between the 91 and the 87 octane. I didnt see but a mile difference in the mpg, Performance I didnt noticed any noticable difference.
But i think different states has different qulifications or specs they require for their gas, and that does effect the mileage ones gets.
True there are even gas stations around that i wouldnt even use for my lawn mower, but i get my gas at a couple of places one guarantees there gas.
I have driven a couple of SS which in MY opion i didnt see much difference if any in the performance over my 2.4, although i do like the looks of the SS at this point wouldnt give mine up for one for now.
So in MY case 87 is just fine, not worth getting in a big up roar over which one to use...93,91,89,87, it got 87 in the first tank, and still gets 87 and it Runs Great.
Senior Member
Joined: 01-22-2008
Posts: 158
From: Oregon
I see this discussion on every turbo forum. People wanting to be cheapskates and use 87 in a car that calls for at least 91 octane. Yeah, drive like a granny 100% of the time and you probably won't notice the loss in power, but punch it to get on the freeway or pass and you'll notice the difference big time. You better hope all of the knock is being taken care of by the computer. Filling up with premium is only another $2-$3 and twice a week is another $4-$6 so for a month it's $16-$24 a month. Wow, real big spenders. I spend that, if not more, on movies every month. So maybe you ought to consider selling your SS and get a Honda if that extra expense is going to break you. 
Senior Member
Joined: 03-31-2008
Posts: 772
From: CLEVELAND
FOR CRYING OUT LOUD. STOP THE MADNESS, $8 PERFORMANCE CHIPS, INTAKES AND EXHAUSTS THAT THROW CODES AND DON'T HAVE DYNOS TO BACK IT UP, 87-94 OCTANE (pertaining to mileage), NITROGEN FILLED TIRES, WATER FOR GAS, CHANGING OIL EVERY 3000 MILES.
STOP IT.
STOP IT.
If you drive your car like a normal (read boring ,plain and lame) dude. Then do this and be happy.
Use 87 octane. I probably get better gas mileage than you, and I do it on 87
Get the picture
Use 94 (or the highest our state offers) if you live for BOOST.
Why not........duh!
Change your oil when the DIC saids, but check it often. Anything more is a waste. If you abuse your car...heat..stop and go...use it as a highspeed taxi...then do it sooner........but ta-da....the magical DIC will tell you to do it sooner....get the picture....
Intakes and exhausts are for looks and sound. Unless one of you can back it up with DATA (I hope you can, and ill buy it)........can you hear the silence.........
Get the picture.
Water for gas???
No comment......
Turbonators???
No comment......
Nitrogen tires in a passenger car????
Buy a pressure gauge, use it frequently. Keep pressures high, but not to high.
Get the picture
$8 performance chip.....
COMMMME OOOONNNN MANNNNNN
I know your smarter then that.
Phew.......in other news a 29y/o male an 0.66 y/o male we spotted in Downtown C-town smiling in their black HHR SS driving down 90 east.
Later Keep HHR-ING
STOP IT.
STOP IT.
If you drive your car like a normal (read boring ,plain and lame) dude. Then do this and be happy.
Use 87 octane. I probably get better gas mileage than you, and I do it on 87
Get the picture
Use 94 (or the highest our state offers) if you live for BOOST.
Why not........duh!
Change your oil when the DIC saids, but check it often. Anything more is a waste. If you abuse your car...heat..stop and go...use it as a highspeed taxi...then do it sooner........but ta-da....the magical DIC will tell you to do it sooner....get the picture....
Intakes and exhausts are for looks and sound. Unless one of you can back it up with DATA (I hope you can, and ill buy it)........can you hear the silence.........
Get the picture.
Water for gas???
No comment......
Turbonators???
No comment......
Nitrogen tires in a passenger car????
Buy a pressure gauge, use it frequently. Keep pressures high, but not to high.
Get the picture
$8 performance chip.....
COMMMME OOOONNNN MANNNNNN
I know your smarter then that.
Phew.......in other news a 29y/o male an 0.66 y/o male we spotted in Downtown C-town smiling in their black HHR SS driving down 90 east.
Later Keep HHR-ING
Last edited by Clevelandhhrss; Jun 13, 2008 at 04:20 PM.
Founding Member
Joined: 11-23-2007
Posts: 8,210
From: Texas
JoeR is right. Our HHRs do not know what octane of fuel is in the vehicle. But they know when they hear more engine noise (a knock or ping) and that information is fed to the ecm which then adjusts the timing. Knocking can be a direct result of low octane fuel so in a way it knows but it doesn't know.
Okay now that that is clear as mud lets talk alcohol.
Alcohol content is measured by readings from the O2 sensors after a fueling event and those are calculated by a predetermined algorithum. The readings are thrown off when adding fuel while it is running because the ecm does not know the vehicle has received new fuel. And that is yet another reason to NEVER fuel your vehicle while it is running, besides the obvious dangers in doing so.
GM will probably modify this method since people are fueling while the vehicle is running and then the next time they try to drive their vehicle it doesn't want to go because it is confused. This is currently only happening on flex-fuel vehicles whose systems are different then current HHRs, but will be similar in 2009.
Okay now that that is clear as mud lets talk alcohol.
Alcohol content is measured by readings from the O2 sensors after a fueling event and those are calculated by a predetermined algorithum. The readings are thrown off when adding fuel while it is running because the ecm does not know the vehicle has received new fuel. And that is yet another reason to NEVER fuel your vehicle while it is running, besides the obvious dangers in doing so.
GM will probably modify this method since people are fueling while the vehicle is running and then the next time they try to drive their vehicle it doesn't want to go because it is confused. This is currently only happening on flex-fuel vehicles whose systems are different then current HHRs, but will be similar in 2009.
Senior Member
Joined: 03-27-2008
Posts: 471
From: Blue Springs Missouri
I see this discussion on every turbo forum. People wanting to be cheapskates and use 87 in a car that calls for at least 91 octane. Yeah, drive like a granny 100% of the time and you probably won't notice the loss in power, but punch it to get on the freeway or pass and you'll notice the difference big time. You better hope all of the knock is being taken care of by the computer. Filling up with premium is only another $2-$3 and twice a week is another $4-$6 so for a month it's $16-$24 a month. Wow, real big spenders. I spend that, if not more, on movies every month. So maybe you ought to consider selling your SS and get a Honda if that extra expense is going to break you.
Drive like a Granny?.....I dont think so...
Punch it on the freeway......... you bet.........thats probablly why i dont get the gas mileage that i might..... passing those guys that get in the way like a granny.
Loss of Power......... Didnt loose a thing....
Sell SS...... mmmmm i dont have one......i have a 2.4
BUY A Honda whats that got to do with it....
IMHO ....... I bought the HHR because I wanted an HHR.....
Everyone has there opioin, and thats whats great about this forum is that you can express your opioin, but to criticized others for their opioin GOOD GRIEF, even if you knew everything ... its pretty bad you have to talk down on us that dont. Thats why we have a forum to learn....... and to get others opioin....
Senior Member
Joined: 06-03-2008
Posts: 123
From: Victoria
If the ECU detects knock (from driving like a maniac with 87 octane, for example) and retards the timing, does the timing eventually get advanced again if you put in 91 octane? Is the ECU always trying to advance the timing as much as the quality of fuel allows, or does it learn bad habits that need to be reset somehow?
Senior Member
Joined: 03-31-2008
Posts: 772
From: CLEVELAND
If the ECU detects knock (from driving like a maniac with 87 octane, for example) and retards the timing, does the timing eventually get advanced again if you put in 91 octane? Is the ECU always trying to advance the timing as much as the quality of fuel allows, or does it learn bad habits that need to be reset somehow?
Founding Member
Joined: 11-23-2007
Posts: 8,210
From: Texas
If the ECU detects knock (from driving like a maniac with 87 octane, for example) and retards the timing, does the timing eventually get advanced again if you put in 91 octane? Is the ECU always trying to advance the timing as much as the quality of fuel allows, or does it learn bad habits that need to be reset somehow?
Senior Member
Joined: 06-03-2008
Posts: 123
From: Victoria
OK, I've heard of older ECUs storing these timing correction factors in memory for long periods of time, or until the ECU is reset, but I guess modern ECUs are a bit more sophisticated than that.
