The OM just says at least 87 octane. Anybody running a higher octane? So far the 87 in mine is running smooth.

From what I've heard, 87 is the spec fuel, but if you put in premium, the engine will recognize the higher octane and will make more power. Anybody confirm?

From what I've heard, 87 is the spec fuel, but if you put in premium, the engine will recognize the higher octane and will make more power. Anybody confirm?

Hmm, more as in more than 361 hp? Or more as in more than you get with regular, up to 361 HP on Premium?

Hmm, more as in more than 361 hp? Or more as in more than you get with regular, up to 361 HP on Premium?

From everything I have read to get the FULL 361hp you need to be running on premium. The car will back off timing to prevent engine knocking on lower grade fuels and it will run just fine. But, you will not be getting the full 361HP on lower grade fuels.

The optimum Octane level depends on the operating climate. The objective is to avoid spark retard which is worst case at hot, high and dry conditions. In these conditions I'd run the highest pump Octane I could get. (example: Denver in the summer)

Cold, humid and low is a natural octane boost so why waist the money when there's no benefit. (example: Seattle in the winter)

I just took mine for a 900 mile road trip. I got 23.0 MPG on 89 oct. It seemed to perform the best with that fuel. 91 oct didn't seem any differently performance wise. 87 oct was getting 19.9 MPG. Of course I was driving like a banshee as often as I could, couple 100+ MPH jaunts. Luckily no speeding ticks!

I'm keeping 93 octane in ours for now since I'll have an HPTuners Suite on the way shortly.

From what I've heard, 87 is the spec fuel, but if you put in premium, the engine will recognize the higher octane and will make more power. Anybody confirm?

Untrue.

If this ECM and OS is like previous models, there are just two timing tables - low octane and high octane. The high octane table is what the vehicle is spec'd to run under, and what it will run 99% of the time. The low octane table exists as a safety measure to prevent you from blowing up your engine with detonation due to bad gas, heavy load, high operating temps, etc.

For examble, if you have 4 passengers and decide to drive your G8 (with 87 octane) from Arizona to San Diego in 100+ degree heat, halfway up the hill your vehicle will likely start knocking. When it does, it will then drop down to the low octane table. Your G8 will use that table until your next fill-up, after which time it will reset to the high octane table.

Now, if you put 89 octane in the tank and make the same trip, the engine may not revert to the lower table. Depending on the severity of the heat, the added load on the vehicle, etc., you may end up getting over the mountains without reverting to the lower table. Putting in 91 or 93 octane will be added insurance against knocking, reverting, and resetting.

As for the OP's question - will you get more power if you put in greater than 87 octane? The answer is no, not unless your vehicle has an aftermarket tune. If you have an aftermarket tune, your tuner will put in higher grade fuel, tune the high octane table by adding more timing, and you will get your added power.

That is the only way you will get more than the SAE certified 361 HP - with an aftermarket tune. Otherwise, your 'extra' octane is either wasted, or simply sits as insurance against less-than-optimal operating conditions. You will see no 'extra' power.

Hope this helps. :driving:

Untrue.

If this ECM and OS is like previous models, there are just two timing tables - low octane and high octane. The high octane table is what the vehicle is spec'd to run under, and what it will run 99% of the time. The low octane table exists as a safety measure to prevent you from blowing up your engine with detonation due to bad gas, heavy load, high operating temps, etc.

For examble, if you have 4 passengers and decide to drive your G8 (with 87 octane) from Arizona to San Diego in 100+ degree heat, halfway up the hill your vehicle will likely start knocking. When it does, it will then drop down to the low octane table. Your G8 will use that table until your next fill-up, after which time it will reset to the high octane table.

Now, if you put 89 octane in the tank and make the same trip, the engine may not revert to the lower table. Depending on the severity of the heat, the added load on the vehicle, etc., you may end up getting over the mountains without reverting to the lower table. Putting in 91 or 93 octane will be added insurance against knocking, reverting, and resetting.

As for the OP's question - will you get more power if you put in greater than 87 octane? The answer is no, not unless your vehicle has an aftermarket tune. If you have an aftermarket tune, your tuner will put in higher grade fuel, tune the high octane table by adding more timing, and you will get your added power.

That is the only way you will get more than the SAE certified 361 HP - with an aftermarket tune. Otherwise, your 'extra' octane is either wasted, or simply sits as insurance against less-than-optimal operating conditions. You will see no 'extra' power.

Hope this helps. :driving:

I would be willing to bet that if you ran 87 octane and dyno'd your car and then dyno the same car with premium you would absolutely see an increase in HP. I do agree it will not be above the rated 361HP but you would see a difference.

In fact I believe I read a thread where someone did just that and there was a jump in HP. Let me see if I can find it.

I'm running 87 currently. Until I have a tune for a higher octane, I'm not wasting money.
I believe it was tuned for 87. Running a higher octane gas will not add timing.

Premium all the way. After 120k miles, my 96 z28's fuel tank was extremely clean when I put a Racetronix in it! Can't say that with cars that came into Goodyear for a new fuel pump (that ran on regular). Those tanks looked mostly dirty.

I would be willing to bet that if you ran 87 octane and dyno'd your car and then dyno the same car with premium you would absolutely see an increase in HP. I do agree it will not be above the rated 361HP but you would see a difference.

In fact I believe I read a thread where someone did just that and there was a jump in HP. Let me see if I can find it.

So what's your wager? :pimp:

i bought this G8 for 2 1/2 weeks, and i have not put gas in it yet. cause the car only got 130 miles.

So what's your wager? :pimp:

I'll buy you lunch if you are ever in DFW, but if I am right you gotta pay for my dyno's. ROFLMAO

In all honesty every car I have had that has been dyno'd has put out a higher # with a higher octane gas. It may not have been a 20hp jump but there was definitely a difference. I just find it hard to believe that it wouldn't make any difference on this as well.

The optimum Octane level depends on the operating climate. The objective is to avoid spark retard which is worst case at hot, high and dry conditions. In these conditions I'd run the highest pump Octane I could get. (example: Denver in the summer)

Cold, humid and low is a natural octane boost so why waist the money when there's no benefit. (example: Seattle in the winter)

I think you are a little confused. Cool air is more dense than hot air, yes, but atmospheric pressure at Sea Level is greater than higher altitudes, ie Denver. Fill up in or around Denver and the highest octane you will probably find is 91 and the lowest 85 or 86. This is because the effective cyclinder pressure is less at the higher altitudes.

Premium is the best way to go. Its worth the extra $1-$3 each fillup.

Premium is the best way to go. Its worth the extra $1-$3 each fillup.

No it isn't. If the vehicle isn't tuned for the higher octane, you are wasting your money.

Premium is the best way to go. Its worth the extra $1-$3 each fillup.

...if the engine is tuned for it.

I think if GM is willing to warranty the g8 for 100k, 87 must be the way to go or they would say premium just to cover their asses!