Reg vs Super
Senior Member
Joined: 07-02-2006
Posts: 164
From: Seattle
Banned
Joined: 10-14-2005
Posts: 9,121
From: Rochester,N.Y.
Screw money, only the best for me. 
My last two vehicles and HHR could use the extra octane. My last car was a modded 02 V6 Mustang that had the computer programmed to run on 93 and if I remember correctly GM recommended premium for my 99 Sunfire GT just like my HHR. On my 89 Grand Am I was probably wasting money but it was a high mileage vehicle and I never had any pinging or anything so maybe it wasn't a waste.
My last two vehicles and HHR could use the extra octane. My last car was a modded 02 V6 Mustang that had the computer programmed to run on 93 and if I remember correctly GM recommended premium for my 99 Sunfire GT just like my HHR. On my 89 Grand Am I was probably wasting money but it was a high mileage vehicle and I never had any pinging or anything so maybe it wasn't a waste.
Senior Member
Joined: 05-22-2007
Posts: 318
From: Huntington Beach, CA
Octane rating does not make the fuel quality better or worse. Higher octane fuel does not burn as easily, that's what helps prevent engines from knocking/pinging/detonation.
If your engine is not knocking and you are putting in anything over regular, you are just burning money.
Put in whatever the manufacture recommends until the end of your warranty. After that, do whatever you want.
When a vehicle equipped with a knock sensor starts knocking, it automatically retards the timing to compensate. Over time, this compensation will decrease the fuel economy.
Knocking usually occurs ONLY during wide open throttle. If you are flooring your gas all the time, you're going to get lower fuel economy regardless of knocking.
If your engine is not knocking and you are putting in anything over regular, you are just burning money.
Put in whatever the manufacture recommends until the end of your warranty. After that, do whatever you want.
When a vehicle equipped with a knock sensor starts knocking, it automatically retards the timing to compensate. Over time, this compensation will decrease the fuel economy.
Knocking usually occurs ONLY during wide open throttle. If you are flooring your gas all the time, you're going to get lower fuel economy regardless of knocking.
Platinum Member
Joined: 05-09-2006
Posts: 6,805
From: "Upland" Mesa, Arizona
Food for thought:
No matter what the octane (which only effects flame propogation rate) rating of the gas, the actual BTU content (energy available) is the same!!
The 2.4 ECM is programmed with two spark timing tables. The engine also has a knock sensor. If knock is detected from say lower octane fuel, the ECM is also programmed to "average down" between the two tables to an ideal advance setting so that knock does not take place.
Whether using low or high octane fuel, the timing self adjusts to optimize for the fuel used.
Bottom line.... It won't and cannot make a difference in fuel mileage. The ability of the ECM to operate in the higher spark advance range with higher octane fuel will result in "slightly" more power, but nothing earth shaking.
No matter what the octane (which only effects flame propogation rate) rating of the gas, the actual BTU content (energy available) is the same!!
The 2.4 ECM is programmed with two spark timing tables. The engine also has a knock sensor. If knock is detected from say lower octane fuel, the ECM is also programmed to "average down" between the two tables to an ideal advance setting so that knock does not take place.
Whether using low or high octane fuel, the timing self adjusts to optimize for the fuel used.
Bottom line.... It won't and cannot make a difference in fuel mileage. The ability of the ECM to operate in the higher spark advance range with higher octane fuel will result in "slightly" more power, but nothing earth shaking.
the programmed parameters in the spark timing tables will not adjust to "sub grade" gasoline....like 85 or 86.
Otherwise, as usual, right on the money.
Banned
Joined: 10-14-2005
Posts: 9,121
From: Rochester,N.Y.
I don't think I've ever seen it at a pump.
Platinum Member
Joined: 05-09-2006
Posts: 6,805
From: "Upland" Mesa, Arizona
Of course, a number of years ago, there was a scandle about a very small chain of independent stations that was using sub grades and lableing it 87. I think the name was something like Brennan.
I guess it depends on the area of the country.....or Mexico.
Senior Member
Joined: 05-13-2006
Posts: 2,334
From: Chicago,IL
Octane rating does not make the fuel quality better or worse. Higher octane fuel does not burn as easily, that's what helps prevent engines from knocking/pinging/detonation.
If your engine is not knocking and you are putting in anything over regular, you are just burning money.
Put in whatever the manufacture recommends until the end of your warranty. After that, do whatever you want.
When a vehicle equipped with a knock sensor starts knocking, it automatically retards the timing to compensate. Over time, this compensation will decrease the fuel economy.
Knocking usually occurs ONLY during wide open throttle. If you are flooring your gas all the time, you're going to get lower fuel economy regardless of knocking.
If your engine is not knocking and you are putting in anything over regular, you are just burning money.
Put in whatever the manufacture recommends until the end of your warranty. After that, do whatever you want.
When a vehicle equipped with a knock sensor starts knocking, it automatically retards the timing to compensate. Over time, this compensation will decrease the fuel economy.
Knocking usually occurs ONLY during wide open throttle. If you are flooring your gas all the time, you're going to get lower fuel economy regardless of knocking.
Other than that, it should not happen, and you certainly can`t expect to get great mileage under those conditions...
Senior Member
Joined: 10-02-2005
Posts: 1,245
From: VA
Tuning is fun! Never seen anything like 85 or 86, but actually the low octane table could be adjusted downward and the car would run fine on it without knock, albeit with a power loss.
Senior Member
Joined: 10-02-2005
Posts: 1,245
From: VA
