I just put the 3rd tank of gas into my new G8 - I am yet to put anything but 93 octane.

Those of you that are putting 87 into it... Can you see a difference in performance? I know the owner's manual says 87 is ok, but I don't quite believe it...

I haven't noticed a difference (except in my pocketbook when I go with 93 instead of 87!)

I haven't noticed a difference (except in my pocketbook when I go with 93 instead of 87!)

Ditto that! I ran the first two tanks with 93, and the last 6 or 7 with 87. No noticeable difference other than a little more coin in my pocket!

is the 93 better for the engine in the long run?

The engine was specifically detuned to run on 87 octane. That's why it's only making 360 HP from 6.0 liters. Prior posts have suggested that the ECU is less likely to retard timing in hot weather with 93 octane, but that's purely speculation. GM's powertrain division is conservative. They wouldn't have designed the engine to approach the knock threshold in anything resembling normal conditions, especially when the same car has to survive Australia.

It makes no difference in the long run which octane you use.

Oh lord, here we go again. :eek2:

The little book that came with the car (not the manual) said that they recomend premium but can put regular. Here is my question. I still have the gas from the dealer in it (just got it 2 days ago) and they put regular. If I have say half or a quarter tank of gas and fill her up with premium and the premium mixes with the regular in the gas tank, is that bad for the car??? I want to put at least 89 octane, preferably 91 but don't know if i have to empty my regular fuel as best I can first.

No, it's not bad for the car. I've only ran 87 in mine, and until I have a tune for a different octane, that's what I'm going to buy.

For an extra $5, the peace of mind is worth it for me to run 93. I'd really like to see if people see a difference in MPG between the two and it would be nice to get back-to-back dyno's.....but that's not as easy as it sounds.

5 bucs is pretty cheap for peace of mind. :)

There isn't any question of safety or the engine lasting longer. The owners manual says it's acceptable to run 87, and I would expect GM to be conservative in regard to damaged engines and warrantee claims. I'm sure it has sophisticated knock sensors, so no worries there.

But why would GM recommend Premium fuel? I can only think of one reason - because premium fuel will allow a more aggressive timing curve. And yes it's more likely to help in hot weather where detonation is more likely, all else equal. It does have 10.2 compression, so how was it detuned to run 87? Most likely by running less ignition advance.

Another thing to consider is that with higher compression engines, better mileage with premium is possible. There is efficiency to be gained by running more ignition advance at low rpm and light to medium loads.

The bottom line is that we are at the educated guess stage regarding what if any improvement is available by using premium. It's hard to do consistent testing to verify .2 in the 1/4 mile or a .5 mpg improvement. One thing that makes it difficult is that PCM strategies typically don't change immediately when you switch fuels. So you can't test on the same day, weather conditions change, etc. It's not like bolting on a part where you can feel or measure the difference right away.

I don't think there is a right or wrong answer here, simply because the exact benefits are unknown, and everyone has different priorities. Personally, I run premium in my 10.5 compression Northstar (same owners manual fuel recommendation as the G8 GT). GM recommends premium for best performance, and the extra cost might be partially offset by an increase in mileage.

There isn't any question of safety or the engine lasting longer. The owners manual says it's acceptable to run 87, and I would expect GM to be conservative in regard to damaged engines and warrantee claims. I'm sure it has sophisticated knock sensors, so no worries there.

But why would GM recommend Premium fuel? I can only think of one reason - because premium fuel will allow a more aggressive timing curve. And yes it's more likely to help in hot weather where detonation is more likely, all else equal. It does have 10.2 compression, so how was it detuned to run 87? Most likely by running less ignition advance.

Another thing to consider is that with higher compression engines, better mileage with premium is possible. There is efficiency to be gained by running more ignition advance at low rpm and light to medium loads.

The bottom line is that we are at the educated guess stage regarding what if any improvement is available by using premium. It's hard to do consistent testing to verify .2 in the 1/4 mile or a .5 mpg improvement. One thing that makes it difficult is that PCM strategies typically don't change immediately when you switch fuels. So you can't test on the same day, weather conditions change, etc. It's not like bolting on a part where you can feel or measure the difference right away.

I don't think there is a right or wrong answer here, simply because the exact benefits are unknown, and everyone has different priorities. Personally, I run premium in my 10.5 compression Northstar (same owners manual fuel recommendation as the G8 GT). GM recommends premium for best performance, and the extra cost might be partially offset by an increase in mileage.

Very well put!

Yea, now I'm starting to think if I would have ran 93 or 94 octane maybe that would of got me into the 13's?

Oh well..... (a tune & CAI definitely will)


...

If I had a G8 I would most likely run premium too, but I would also look into a retune for that also. Premium is .20 to .30 higher per gallon for 92/93 octane vs 87. So on a 14-15 gallon fillup your only spending $3, $4 extra tops. For piece of mind, possible mpg? and possible hp? I'd say it might be worth it.

It doesn't matter what grade of gas your buying right now, they are all expensive.

Here premium is over $4/gal, regular is still in the $3.80-$3.95 range, so mise well go with premium because you are entitled to bitch more when it passed $4/gal.... lol

I don't think there is a right or wrong answer here, simply because the exact benefits are unknown, and everyone has different priorities. Personally, I run premium in my 10.5 compression Northstar (same owners manual fuel recommendation as the G8 GT). GM recommends premium for best performance, and the extra cost might be partially offset by an increase in mileage.

I agree with JLockhart and look at it this way: For $3-4 per tank it certainly can't hurt to run premium.

I've come to the decision to run 93 octane in my G8. This is not because I think it's going to give me any instantaneous power bump in all circumstances. But after distilling some of the good conversations on this board and other information that has been linked to, it appears to me that the V8 is optimized for 93 octane but can be safely run on 87. Also, I live where it is hot much of the year and my foot is heavy. Based on my understanding of the issue, 93 octane will serve me better.

As always, YMMV.

So based on all of this dialogue of 87 vs. 90 something, who actually has the cleaner burning gas in the market place these days (Mobil, Sunoco, Shell, BP, etc.)? What I mean by "cleaner" burning, these places all tought they have cleaner gas to prevent fuel injector build up, etc. I think that plays into this conversation as well.

Opinions? (sorry if this should be a new thread, just felt appropriate)

Oh lord, here we go again. :eek2:

and again and again and again....

So based on all of this dialogue of 87 vs. 90 something, who actually has the cleaner burning gas in the market place these days (Mobil, Sunoco, Shell, BP, etc.)? What I mean by "cleaner" burning, these places all tought they have cleaner gas to prevent fuel injector build up, etc. I think that plays into this conversation as well.

Opinions? (sorry if this should be a new thread, just felt appropriate)

For what it's worth, my mechanic, who has raced GM products for 40 years, recommends using ONLY BP Ultimate in any car to keep the injectors clean. He claims that he's never changed an injector in a car that used Ultimate (old Amoco Gold) but has changed plenty for all other fuels, including lower BP grades.

I have one data point, my 1999 Buick Regal GSE, which required premium and in which I ran Gold/Ultimate for 100,000 miles (except for a handful of times when I could not find a BP station). My mechanic bought the car when I got my G8, so he was willing to put his money where his mouth was.

I have attempted to convince my wife to run Ultimate in her 2006 Torrent but you know how that goes. Plus, she has time for her car to be in the shop for new injectors--I don't. No way I will ever get my kids to run premium in the Jeep Liberty; but I bought it used and it's got a 100k powertrain warranty, so who cares.

In 2 or 3 years I'll have 3 more data points....

and again and again and again....

Well, it's more fun than the XM radio/navigation debates elsewhere...:)

So based on all of this dialogue of 87 vs. 90 something, who actually has the cleaner burning gas in the market place these days (Mobil, Sunoco, Shell, BP, etc.)? What I mean by "cleaner" burning, these places all tought they have cleaner gas to prevent fuel injector build up, etc. I think that plays into this conversation as well.

Opinions? (sorry if this should be a new thread, just felt appropriate)
My motorcycle mechanic, who has lots of years building up high-performance racing engines, is partial to Chevron. He claims that the additive package is superior to other brands in keeping the carbon buildup on valves, etc., to a minimum.

The LS1 GTO was the same way as the G8. Premium was recommended but 87 was allowed. Nearly everyone runs premium in them because they noticed there's a significant drop-off in mileage (and power, for that matter) when running 87. From what I've read though, the G8 is tuned to run on 87, so you probably won't see much of a bump in power running 93. What you will see is possibly slightly better mileage and definitely less harmful detonation in the engine. Plus, as has been seen, these cars are a quick 93-octane tune away from 20-30 more horsepower so there's a lot on the table. The LS2 in the GTO requires premium and will go to a low-octane table if too much knock is detected.

As for gasoline, I agree with running BP Ultimate. I've tried other fuels in my GTO and get a LOT more detonation and noticeably worse mileage/power, especially the cheap stuff. I tried Kroger brand 93 once thinking "all fuel's the same, right?" Boy was I wrong...the car ran like crap. I've never had a problem with BP.

I just purchased a 2008 G8 GT 4 days ago. The dealership, I am assuming, put in 87 octane and i have notice that when I am sitting at a stop light the engine does not run smoothly. The manual does recommend 87 octane however I have read in multiple places online that it should run on preimum, specifically Motor Trend had the fuel listed as preimum. I am going to run it on mid grade and see how it preforms.

A couple of additional things that I have notice is that the G8 really doesn't like running between 30-35 mph, it seems like there is a lot of vibration from the transmission and it has a hard time selecting the right gear to be in. Has anyone else noticed this?

The lack of XM radio is really disappointing and the guy at the dealership told me it was because GM is unsure what is going to happen with the merger of XM and Sirus so they decided to leave it out of the G8.

Finally, I have the 6 disc CD changer with the big display screen and I find it highly annoying that you cannot change the display screen above the radio to display something besides the battery charge and oil pressure.

Outside of those things, I really like the car and she is so much faster than my 2004 Grand Prix GTP.

I just purchased a 2008 G8 GT 4 days ago. The dealership, I am assuming, put in 87 octane and i have notice that when I am sitting at a stop light the engine does not run smoothly. The manual does recommend 87 octane however I have read in multiple places online that it should run on preimum, specifically Motor Trend had the fuel listed as preimum. I am going to run it on mid grade and see how it preforms.

A couple of additional things that I have notice is that the G8 really doesn't like running between 30-35 mph, it seems like there is a lot of vibration from the transmission and it has a hard time selecting the right gear to be in. Has anyone else noticed this?

The lack of XM radio is really disappointing and the guy at the dealership told me it was because GM is unsure what is going to happen with the merger of XM and Sirus so they decided to leave it out of the G8.

Finally, I have the 6 disc CD changer with the big display screen and I find it highly annoying that you cannot change the display screen above the radio to display something besides the battery charge and oil pressure.

Outside of those things, I really like the car and she is so much faster than my 2004 Grand Prix GTP.

You car is not vibrating because of the fuel. Many people have reported the same exact thing.

Same thing with the transmission. The shift points suck. It seems to hunt quite a bit for what it wants to do. VMS can tune the TCM. It is well worth it imo. Night and day difference.

You dealer is idiot. They did not exclude XM because they don't know what is going to happen. I am not sure that Holden puts satellite radio in any of it's cars. Hell, it may not even be an option down there at all. It's pretty obvious what's going to happen. They are merging. LOL They have said many times that the merger will not effect existing software. There will be no need for everyone to go and buy new equipment after the merge.

Join the club on the gauges. Hopefully, someone comes out with an affordable solution to this soon.

Congrats on the new car and have fun with it.

I just purchased a 2008 G8 GT 4 days ago. The dealership, I am assuming, put in 87 octane and i have notice that when I am sitting at a stop light the engine does not run smoothly. The manual does recommend 87 octane however I have read in multiple places online that it should run on preimum, specifically Motor Trend had the fuel listed as preimum. I am going to run it on mid grade and see how it preforms.

A couple of additional things that I have notice is that the G8 really doesn't like running between 30-35 mph, it seems like there is a lot of vibration from the transmission and it has a hard time selecting the right gear to be in. Has anyone else noticed this?

The lack of XM radio is really disappointing and the guy at the dealership told me it was because GM is unsure what is going to happen with the merger of XM and Sirus so they decided to leave it out of the G8.

Finally, I have the 6 disc CD changer with the big display screen and I find it highly annoying that you cannot change the display screen above the radio to display something besides the battery charge and oil pressure.

I'm mostly going to agree with everything dodson said.

1. All the V8s seem to have a lumpy idle. It's not related to gas.

2. The vibration you are feeling at the 35 - 40 mph range is likely the AFM / DoD kicking in. With the engine running on 4 cylinders there is noticeable vibration.

3. Yes, your dealer is an idiot regarding XM. If you want XM you can use an add-on unit and plug it into the AUX input.

4. We all hate that center gauge.

Great car, though, enjoy!

Babe Ruth Fan - in regards to your rough engine at idle... Myself and many others on this board have experienced it. I've seen everything from "what do you expect? its a V8!!" to "I took mine back to the dealership and they adjusted the PCM and now its fine", so I'm not sure what to think.

Personally, I understand that my G8 has "a big V8", but I also don't expect a brand new car to be rough, almost sputtering at times, when sitting at idle.

I'm anxious to take mine in next week to the dealership and speak to the mechanics myself. Other than the rough idle, I'm 100% happy with it.

I felt the same vibration today. I felt it mostly in the gas pedal. that's AFM?

Thanks for the info. My pops has a LTZ Impala and he has complained about the vibration at the same speeds as I have been experiencing. I will pass the info onto him too as I am sure they are some what related.

You are going to tell me that during the entire design process no one thought that the driver wouldn't want to look at a display that showed oil pressure and the battery charge? They should have just went with the display that they had in the Grand Prix which displayed pretty much everything that you wanted to know and you could actually adjust what you were looking at. It is a digital display so someone will come up with some way to adjust it sooner or later or at least I hope so.

Has anyone put an aftermarket XM system in their G8's? I am looking into that but haven't actually had any time to talk to anyone about it. I am concerned about them having to drill holes in the car for the antenna.

Thanks for the info. My pops has a LTZ Impala and he has complained about the vibration at the same speeds as I have been experiencing. I will pass the info onto him too as I am sure they are some what related.

You are going to tell me that during the entire design process no one thought that the driver wouldn't want to look at a display that showed oil pressure and the battery charge? They should have just went with the display that they had in the Grand Prix which displayed pretty much everything that you wanted to know and you could actually adjust what you were looking at. It is a digital display so someone will come up with some way to adjust it sooner or later or at least I hope so.

Has anyone put an aftermarket XM system in their G8's? I am looking into that but haven't actually had any time to talk to anyone about it. I am concerned about them having to drill holes in the car for the antenna.

You shouldn't have to drill holes to mount the antenna. I have sirius and they offer a magnetic antenna. I am sure XM has something similar.

BRF, your dad's engine is only a 5.3, runs east and west instead of north/south. It could have vibration from AFM but should be felt in a different plane.


Guys, when talking fuel, don't forget that regardless of the octane, GM (and BMW, etc, etc) all highly recommend Top Tier Gas (http://www.toptiergas.com/) I know BP Ultimate exceeds the standards but their lower grades do not.

I felt the same vibration today. I felt it mostly in the gas pedal. that's AFM?
Yep. I can feel it through the pedal and the steering wheel.

Yep. I can feel it through the pedal and the steering wheel.

Change the exhaust and you can hear the difference quite a bit as well. It's not too bad but it's definitely a noticeable difference.

What kind of mileage are you guys gettin??

http://img378.imageshack.us/img378/5865/picture045ar9.th.jpg (http://img378.imageshack.us/my.php?image=picture045ar9.jpg)

YIKES!

What kind of mileage are you guys gettin??

http://img378.imageshack.us/img378/5865/picture045ar9.th.jpg (http://img378.imageshack.us/my.php?image=picture045ar9.jpg)

YIKES!

Try getting your foot out of the skinny pedal so much and I am sure it will get better. LOL Good luck with that btw.

Reset it and take it easy on her and see what it does to those numbers.

When I'm being a good boy I average around 18 - 19 mpg in combined driving. Lately as the engine has been getting closer to being fully broken in it's been closer to 15 mpg because I can't keep my foot out of it.

I'm right at 19.5 in combined driving.

I find BP seems to clean out the engine, almost like adding some Gumout or similar product. Not to many top tier gas dealers in my area...surprised Exxon not on the list.

I go to mostly Shell or Chevron. I don't think we have many if any BP's around here.

I go to mostly Shell or Chevron. I don't think we have many if any BP's around here.
We had a couple of BPs on the west side of Fort Worth for a couple of years but they're gone now....

We had a couple of BPs on the west side of Fort Worth for a couple of years but they're gone now....

Yeah, I just searched their site and there is not one within a 50 mile radius of my zip code. I guess my car is going to blow up now. :gr_jest:

BRF, your dad's engine is only a 5.3, runs east and west instead of north/south. It could have vibration from AFM but should be felt in a different plane.


Guys, when talking fuel, don't forget that regardless of the octane, GM (and BMW, etc, etc) all highly recommend Top Tier Gas (http://www.toptiergas.com/) I know BP Ultimate exceeds the standards but their lower grades do not.

Sun of a... I only have the Turkey Hill's around here. And the closest one is about 50mi away...

I gas up at a BP near my home, and for the last 2 years, I got the best gas mileage using their fuel. I may bump up my octane to 91. See what happens. LOL

I have been using Mobil, but now you got me thinking BP is what I should be using. It's usually a bit higher than the rest... maybe now I know why? :-)

XM's antenna is magnetic. But... if you want to mount it directly below the radio/onstar antenna on the glass, use industrial velco! Works like a charm. As for the vibration that all of us are experiencing under low load conditions, think of it like Aussi karma! Or... just enjoy it like when you're waiting to be seated at "Outback".

RRM

Does anyone have any (trustworthy) reference articles that sheds some light on using low octane vs high octane gas?


From the discussion, I picked up the following hints:
Use top tier gasolines (Chevron, BP, Exxon) for better quality, they have additives that help clean the injectors and valves, possibly better gas mileage
If you nornally use 87 octane, run a higher octane number in hotter weather to prevent detonation
The ECU will retard engine timing to prevent knocking
Will higher octane gas yield better gas mileage?
Did I miss anything?

What kind of mileage are you guys gettin??

http://img378.imageshack.us/img378/5865/picture045ar9.th.jpg (http://img378.imageshack.us/my.php?image=picture045ar9.jpg)

YIKES!

Yea.. with your average speed a little over 14mph, You like seeing how fast you can get to the next red light I see :p

My car has been averaging a combined 18mpg. I just installed the Roto Fab CAI yesterday and for the first time put in about 9 gallons of 93. Should have just put 87, but anywho. Monday I'm going to look and see what kind of mileage she's showing. My wife drives the car on a 35mile round trip to work all this weekend and she baby's it. Me on the other hand, I barely get to drive it. So when I hope in, it's showing 18mpg, and when I get out from a 20mile drive, I'm showing about 12mpg...

I have now recently been driving with the lightest foot I possibly can, average speed is 12.2 MPH and my mileage is 9.6. I don't understand. Everyone else is reading imbetween 14 and 18. My car seems to be really thirsty. The only other difference is instead of the 87 octane the dealer put in, I now put in 93 Octane gas from Sonoco. Would that make mileage worse? I heard premium gas is supposed to make it better.

I have now recently been driving with the lightest foot I possibly can, average speed is 12.2 MPH and my mileage is 9.6. I don't understand. Everyone else is reading imbetween 14 and 18. My car seems to be really thirsty. The only other difference is instead of the 87 octane the dealer put in, I now put in 93 Octane gas from Sonoco. Would that make mileage worse? I heard premium gas is supposed to make it better.

Did you reset it? Also, try doing the mileage by hand instead of doing it off the computer.

Did you reset it? Also, try doing the mileage by hand instead of doing it off the computer.

How do I reset it? Sorry if this is obvious

Hold down the enter button and it should clear out all the data. I personally would write down your mileage next time you fill up. Then when you get gas after that see how many miles you had driven and divide it by how much gas you just filled up with. I know the mpg computer in my truck is fairly close but it's not exact by any means.

sounds like a better idea. I reset it and the numbers are in the 10 and 11 range

I've come to the decision to run 93 octane in my G8. This is not because I think it's going to give me any instantaneous power bump in all circumstances. But after distilling some of the good conversations on this board and other information that has been linked to, it appears to me that the V8 is optimized for 93 octane but can be safely run on 87. Also, I live where it is hot much of the year and my foot is heavy. Based on my understanding of the issue, 93 octane will serve me better.

As always, YMMV.
BP 93 is the best. So far.

I drive all city for now. I'm not seein any number over 12 mpg and that's with a ridiculous light foot. RPM not even hitting 1500 rpm. Going extremely slow and light and I get 12.4. Going normal I get about 10. Slight heavy foot about 9.4

I ran 91 in my G8. Surprisingly I got 21.2 in combind driving. Better than the 19.5 I've been getting. When I used a calc to check against the DIC, it was .2 mpg off on 330 miles.
calc= 20.958
DIC= 21.2
So, I put another tank of 91 in it and had the mileage up to 24. It's back to 20.4 now though. :)

I ran 91 in my G8. Surprisingly I got 21.2 in combind driving. Better than the 19.5 I've been getting. When I used a calc to check against the DIC, it was .2 mpg off on 330 miles.
calc= 20.958
DIC= 21.2
So, I put another tank of 91 in it and had the mileage up to 24. It's back to 20.4 now though. :)

What is your secret? Maybe mine has to break in or it 93 Octane fuel too high?

I understand how the AFM works. I work on getting that working in my favor.

I run BP 93 and get 15-17 for around-town driving. If I do any expressway cruising at all I'm close to 20, and for the two all expressway runs I got over 20 mpg, but the car had less than 1000 miles on it.

Wow, I'm with most everyone else on this board. I'm getting about 17-19 mpg in combined driving. I reset it yesterday on the way home from work when I got on the highway and got 23.2 on the highway.

I will turn 1000 miles on my way home tonight, so now that its "officially" broken in, I may see that go waaaay down :-)

The LS1 GTO was the same way as the G8. Premium was recommended but 87 was allowed. Nearly everyone runs premium in them because they noticed there's a significant drop-off in mileage (and power, for that matter) when running 87.
.

30 mpg here on 87 in July Heat and humidity fully loaded car

Mines around 15.8avg.on 93 octane I think.

I just purchased a 2008 G8 GT 4 days ago. The dealership, I am assuming, put in 87 octane and i have notice that when I am sitting at a stop light the engine does not run smoothly. The manual does recommend 87 octane however I have read in multiple places online that it should run on preimum, specifically Motor Trend had the fuel listed as preimum. I am going to run it on mid grade and see how it preforms.

A couple of additional things that I have notice is that the G8 really doesn't like running between 30-35 mph, it seems like there is a lot of vibration from the transmission and it has a hard time selecting the right gear to be in. Has anyone else noticed this?

The lack of XM radio is really disappointing and the guy at the dealership told me it was because GM is unsure what is going to happen with the merger of XM and Sirus so they decided to leave it out of the G8.

Finally, I have the 6 disc CD changer with the big display screen and I find it highly annoying that you cannot change the display screen above the radio to display something besides the battery charge and oil pressure.

Outside of those things, I really like the car and she is so much faster than my 2004 Grand Prix GTP.

Hey, i have a cool tip for you that you should try. I am quoting from another blog website called G8GT.com.
"Tip: Engineering Mode

Next time you get into your G8 give this a try. Hold down the enter key while cranking (Turning the ignition key). You'll enter engineering mode where you can see a couple of cool things."

Some of the cool things he is referring to are, "gal/hr, gear your in, Gal of fuel left, Voltage, tranny temp, and a whole bunch more."
You can also see, "... % of charge of battery various fluid temperatures, etc."

Alright my man, I hope this helps you out. By what I hear at the other blog site, you should have a good time with this information.:driving: