I read somewhere else on these forums that you will actually get more power out of your STOCK G8 GT if you use regular 87 octane fuel than if you use premium fuel. Is this true????? I've been putting in 93 Octane

no clue. i got the car on sat and have not yet put gas in it. tomorrow i will have to as my low gas light is on and engineer mode says i have 2 gallons left before i am pushin it. i am going to put in regular. if i go to track, then premium, but engine is tuned and made for 87, so why not put in 87?

if its tuned for 87, use 87.

Here we go again!

I have had my G8 GT a month and have already put 3000 miles on her using only 87. So far avg 25 pure highway and 14-18 mixed city. Better than my '04 V6 GTP.

I have put about 2000 on my car in one month and i am also getting better gas milage then my 05 GP

I mean power not mileage from using 87. Something about the higher octane being harder to burn for the way the engine is tuned or something.

Here we go again!

Again? If there's another thread about this give me a link. I couldn't find one about this just about octane and mileage.

Again? If there's another thread about this give me a link. I couldn't find one about this just about octane and mileage.

It's been stated that these cars come tuned to 87 octane.

Using 89 or higher is said to be a waste of money unless your car is tuned to that octane. Car's are computers now, everything needs to be programed these days.

I have no idea of where the thread is, but I've read it.

I think some of the confusion started because some of the car magazines indicated the car uses Premium fuel. But if people would just read the owners manual, it clearly says 87 octane.

I have had my G8 GT a month and have already put 3000 miles on her using only 87. So far avg 25 pure highway and 14-18 mixed city. Better than my '04 V6 GTP.

Same here! I am getting better mileage on my G8 GT than on my 2004 Grand Prix GTP. Amazing, huh?

Again? If there's another thread about this give me a link. I couldn't find one about this just about octane and mileage.

This has been discussed on one more than one thread. Just do a search and you'll find the discussions. In one camp were people saying that anything more than 87 will not do squat since this car is tuned for 87. In the other camp were folks saying that 93 is not that much more money, but you'll get better mileage and protect your engine.

Who to believe?

And it's true that some car magazines were reporting 93, which only added to the confusion.

Who to believe?



Someone with a dyno and back to back runs on different fuels. We don't really have that, just the tuners all tuning for 93.

Now, as I have said before, EPA site says the car was emissions and mpg certified on premium (which means 89 at a minimum). Pontiac's own info says the car will run fine on 87 but they recommend premium. No exact info on SAE certification as to which fuel is used - but here is my $.02 again. My belief is that the engine produces full SAE rated power on and is factory tuned for 93. http://media.gm.com/us/powertrain/en/product_services/2008/Spec%20Sheet/Gen%20IV/2008%20Gen%20IV%20Car/08_L76.xls
Because of knock sensors and spark retarders it is a simple matter for the engine to automatically degrade itself when fed 87 octane.

Now the "other" GM recommendation that is important: Top Tier Gas. Not every 87 meets the standard, even if the brands 93 exceeds it.

Maybe VMS can chime in here. Unless the car has three tables, I find it highly unlikely that our cars will take advantage of higher octane fuel. If they recommend 87 (manual), then there has to be another table for fuel that is lower quality (winter gas). That means, there has to be a third table for higher octane. Dunno.

It totally depends on the engine's operating conditions. There is actually more potential energy in regular then premium. However the octane in premium will help prevent spark retard.

If the engine detects knock it will revert to a much more conservative timing table. This will result in spark retard and less performance from the engine. Knock potential is worst case in hot, dry and heavy engine demand conditions.

If the operating environment of the engine is such that knock is never detected then you're waisting money buying premium.

I generally buy premium in the summer but use regular the rest of the year when it's wet and cold. I also avoid premium if I'm on the freeway trip since the engine is under very little load.

Buying premium is nothing more then an insurance policy against the engine reverting to a lower performance timing table.

Buying premium is nothing more then an insurance policy against the engine reverting to a lower performance timing table.
I think that summarizes the issue nicely.

Buying premium is nothing more then an insurance policy against the engine reverting to a lower performance timing table.

Which means 89 is good 'nuff

Which means 89 is good 'nuff

So unless you're gonna go racing, 89 (or even 87) is fine.
(and will save you hundreds of dollars over the course of the year).

So unless you're gonna go racing, 89 (or even 87) is fine.
(and will save you hundreds of dollars over the course of the year).

Assume 15,000 miles per year @ 18 mpg combined @ $.10 difference in price and you'll only spend $83/year more. If you could increase your mpg by 1 you would save about 50 gallons, then you're talking a couple hundred dollars.

Mine ran on 87 from KC to Glens Falls, NY with no problem and got 21.5 mpg @ 85 mph, 22.3 mpg @ 80 mph and 25 mpg (for about a 140 mile stretch) @ 75 mph.

I ran the 87 because ambient temps were in the 50's to low 70's.

Around Tucson, I only run 91 (they don't see fit to supply 93:(). I do that because bumper-to-bumper traffic in 100° temps is just begging for detonation.

So unless you're gonna go racing, 89 (or even 87) is fine.
(and will save you hundreds of dollars over the course of the year).

No, use 87 normally and 89 for racing. Anything above is a waste.

Assume 15,000 miles per year @ 18 mpg combined @ $.10 difference in price and you'll only spend $83/year more. If you could increase your mpg by 1 you would save about 50 gallons, then you're talking a couple hundred dollars.

Um, higher octane fuel is HARDER to burn. Therefor, you get WORSE mileage using it, because its coming out the exhaust. So, you're not only paying $83 more a year, but you're using more fuel, which -1mpg difference at 15,000... 20 versus 19. 39 gallons more a year, at, oh, lets be conservative and say $3.50. $136/yr more, just to be cool.

Hey, by all means. Spend you're $200+ dollars anyway you want, but I'll save mine for stuff that matters, like a CAI that actually improves mileage.

Now, if you want to get a VMS tune, for 91 octane, I can do the math and show how it'll pay for itself in at most, 2 years.

Um, higher octane fuel is HARDER to burn. Therefor, you get WORSE mileage using it, because its coming out the exhaust. So, you're not only paying $83 more a year, but you're using more fuel, which -1mpg difference at 15,000... 20 versus 19. 39 gallons more a year, at, oh, lets be conservative and say $3.50. $136/yr more, just to be cool.

Hey, by all means. Spend you're $200+ dollars anyway you want, but I'll save mine for stuff that matters, like a CAI that actually improves mileage.

Now, if you want to get a VMS tune, for 91 octane, I can do the math and show how it'll pay for itself in at most, 2 years.

yes I want a VMS tune and am going to get it in the near future. I have noticed better mileage with regular fuel on this car. That will change with the tune?

If Vector tunes it for 91 you will get your best performance and mileage with 91.

If Vector tunes it for 91 you will get your best performance and mileage with 91.

should i get it tuned for 93? Thats an option. Do all gas stations have 93 octane fuel?

You'll get your best horse power increase on the 93 tune. Not all stations sell 93 octane. However, it isn't a problem if you're force to buy 91 on a 93 octane tune.
You don't have your location in your profile, but you can get 94 in Indiana.

You'll get your best horse power increase on the 93 tune. Not all stations sell 93 octane. However, it isn't a problem if you're force to buy 91 on a 93 octane tune.
You don't have your location in your profile, but you can get 94 in Indiana.


The only gas stations in New England (that I've seen) that sell above 91 is Sunoco. They sell 93. Kind of limiting in my book. Then again, there is a sunoco station that sells 100 about 5 miles away from me, unleaded too. :)

why cant they make a tune for 87 octane? fix the shift points or lean it out, whatever the case may be.

why cant they make a tune for 87 octane? fix the shift points or lean it out, whatever the case may be.

Who said they cannot? As VMS has stated, the cars run pig rich from the factory. Leaning it out a LOT, while still being tuned for 87, should yield some decent power numbers. I just think, if you want the claimed 20rwhp, you're going to have to bump up the octane requirement, which allows you to use more aggressive timing/spark settings.

i would love a tune for 87 octane that would produce maybe 1 - 2 more mpg with the intake. I think A LOT of people would be interested if they could come up with a tune for 87 to have good shift points, lean it out, make a little more power and add some MPG. These cars are extremely rich. Just look at your exhaust tips after you drive it for a little while. Black inside.

If there was a tune for 87 for 1-2MPG these cars would already have it (especially with CAFE these days.) Again there is NO POINT in retuning a car for 87 thats already tuned for it LOL You arent going to get any more power or MPG. The whole point of the tune is to get MORE fuel economy to offset the cost of premium fuel. IE Premium costs LESS than regular in the long run :)

If there was a tune for 87 for 1-2MPG these cars would already have it (especially with CAFE these days.) Again there is NO POINT in retuning a car for 87 thats already tuned for it LOL You arent going to get any more power or MPG. The whole point of the tune is to get MORE fuel economy to offset the cost of premium fuel. IE Premium costs LESS than regular in the long run :)


*BZZZT* Thank you for playing, please try again. The manufacturer uses an extreme safe tune, to ensure a lengthy life of the motor. Rich is always safe (assuming you don't go too far). I've personally owned vehicles that were re-tuned for 87 and experienced both increased power (15rwhp) and increase fuel economy (1-2mpg). The LT1's were perfect examples of super safe tunes from the factory. Seeing what VMS is stating here, as well as some others, it looks like the L76 is no different.

so are you saying VMS is wrong?

Yes there def is room to re-tune the current system on 87 octane. GM didnt go aggresive with there stock settings. If Vector or someone could tune the car at 87 and make it better, myself and others would be very interested. Fixing the shift points, leaning it out, all that would help the car. Not everyone wants to run 93 octane. And no matter how you slice it, paying $650 for the intake and tune, and paying more for premium, the costs dont really even themselves out like everyone keeps saying. So, when someone comes out wit an 87 tune, I will be picking that up. I dont need to gain 50 hp to be happy. I LOVE driving this car, but with the gas going insane, I dont drive it as much as I would if gas was cheaper. And I DO NOT want to pay for premium to go into this car. At the track, yes. But daily driving, no. Just my opinion.

Yes there def is room to re-tune the current system on 87 octane. GM didnt go aggresive with there stock settings. If Vector or someone could tune the car at 87 and make it better, myself and others would be very interested. Fixing the shift points, leaning it out, all that would help the car. Not everyone wants to run 93 octane. And no matter how you slice it, paying $650 for the intake and tune, and paying more for premium, the costs dont really even themselves out like everyone keeps saying. So, when someone comes out wit an 87 tune, I will be picking that up. I dont need to gain 50 hp to be happy. I LOVE driving this car, but with the gas going insane, I dont drive it as much as I would if gas was cheaper. And I DO NOT want to pay for premium to go into this car. At the track, yes. But daily driving, no. Just my opinion.

I already did the math in another thread. Using premium over regular, on a typical 15,000 mile/yr cycle, only costs about $100 more. Like others have said, if you wanted fuel mileage and were concerned about gas prices, you should have bought a honda.

HOWEVER, the tune is well worth it for the performance gain. It only takes about 15rwhp for a person to notice a significant difference. If we're talking 30rwhp with a CAI and tune, that's pretty awesome. If we manage to acquire additional fuel economy, that's just icing on the cake, but it shouldn't be what you're looking for, because it won't pay itself off, unless you keep the car for a very very long time (5+ years)

If there was a tune for 87 for 1-2MPG these cars would already have it (especially with CAFE these days.) Again there is NO POINT in retuning a car for 87 thats already tuned for it LOL You arent going to get any more power or MPG. The whole point of the tune is to get MORE fuel economy to offset the cost of premium fuel. IE Premium costs LESS than regular in the long run :)


Thats correct, the car is rich from the factory because it runs a decent amount of timing and has relatively high compression. The extra fuel keeps preignition to a minimum when utilizing 87 octane. There really is no point to tuning it on 87 octane, if there was GM would already be doing it.

Lets break it down:

If you drove 10,000 miles in a year, all maxed highway MPG, and used all 19 gallons:

456 miles = 19 gal X 24 MPG
513 miles = 19 gal X 27 MPG (VMS estimates 2-3 MPG gain, well go with 3)

Driving 10,000 miles in a year, getting 456 miles on a single tank, you would have to fill up 22 times on 87 octane

Driving 10,000 miles in a year, getting 513 miles on a single tank, you would have to fill up 20 times on 93 octane

$1,672 = 22 fill ups at $4.00 a gal 87 octane
$1,596 = 20 fill ups at $4.20 a gal 93 octane (premium is AT LEAST .20 more expensive)

For 5 years on 87 octane at $1,672 = $8,360 (assume 87 gas stays at $4.00/gal)
For 5 years on 93 octane at $1,596 = $7,980 (assume 93 gas stays at $4.20/gal)

VMS tune and intake = $650

To drive on 87 octane for 5 years would cost = $8,360
To drive on 93 octane for 5 years with the intake and tune = $8,630
Difference of = $270

In the long run, you end up spending more, and thats saying you got 3 more MPG. Some people are seeing 2 and others havent seen anything. So, I know these numbers a little vague and other things you have to take into account, but the long run isnt as cheap and equal as people think. $270 difference is not that bad though, but if you get get 1 more MPG on regular octane, it would make it that much better. And of course, if you drove your car 20,000 miles in a year, it would work out better. All depends on your driving style.

Lets break it down:

If you drove 10,000 miles in a year, all maxed highway MPG, and used all 19 gallons:

456 miles = 19 gal X 24 MPG
513 miles = 19 gal X 27 MPG (VMS estimates 2-3 MPG gain, well go with 3)

Driving 10,000 miles in a year, getting 456 miles on a single tank, you would have to fill up 22 times on 87 octane

Driving 10,000 miles in a year, getting 513 miles on a single tank, you would have to fill up 20 times on 93 octane

$1,672 = 22 fill ups at $4.00 a gal 87 octane
$1,596 = 20 fill ups at $4.20 a gal 93 octane (premium is AT LEAST .20 more expensive)

For 5 years on 87 octane at $1,672 = $8,360 (assume 87 gas stays at $4.00/gal)
For 5 years on 93 octane at $1,596 = $7,980 (assume 93 gas stays at $4.20/gal)

VMS tune and intake = $650

To drive on 87 octane for 5 years would cost = $8,360
To drive on 93 octane for 5 years with the intake and tune = $8,630
Difference of = $270

In the long run, you end up spending more, and thats saying you got 3 more MPG. Some people are seeing 2 and others havent seen anything. So, I know these numbers a little vague and other things you have to take into account, but the long run isnt as cheap and equal as people think. $270 difference is not that bad though, but if you get get 1 more MPG on regular octane, it would make it that much better.

Thats a pretty fair comparison there, the point of the tune isnt to SAVE money (although sometimes it works out that way :)) but to simply negate the extra cost for premium so you get more power and performance WITHOUT spending more. Typically thats how it works out, but as usual YMMV.

[QUOTE=h3llphyre;47545]Like others have said, if you wanted fuel mileage and were concerned about gas prices, you should have bought a honda.QUOTE]

Thats just ignorant. Because I am concerned about gas mileage and want good gas mileage, I might as well blow up the car and go buy a Prius correct? I dont even want to get into it with people like you because its a waste of time and energy

and I do respect the tune, not like i got anything against VMS. I am just curious as to the possibility of a tune to fix the shift points, lean it out, and with an intake, pick up 10-15 HP and 1 MPG. That's all I was lookin for

Thats just ignorant. Because I am concerned about gas mileage and want good gas mileage, I might as well blow up the car and go buy a Prius correct? I dont even want to get into it with people like you because its a waste of time and energy


Its not ignorant, I'm being realistic. The cost of the Tune + CAI will take a very long time to pay off, if you're thinking purely in terms of fuel economy. Look above, its been shown. The only reason to go for the tune+CAI is for performance, with the slight increase in economy being an added bonus.

You don't buy a 20mpg car if you're concerned with fuel prices. I did all the math out before I bought the car, to determine the cost difference between the G8 and my old daily (40mpg), to ensure it wouldn't hurt me financially. 1-2mpg isn't going to make a huge difference at the end of the day.

i actually just traded in my G8 GT for a for a sweet Huffy bicycle. Now I dont have to worry about gas at all.