At the moment we are getting 17.5 on our DIC. I'm very surprised as we do mostly City driving and we drive it hard too!!

The DOD is noticeable from the drivers seat and kind of annoying but I think we will get used to it..

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2007 Trailblazer SS Cammed!
2008 G8 GT Magnetic Grey Metallic #685

I just ran out my tank of 87oct 220miles and beating the shit out of it . DOD I'm turning off .

I got 21.059 mpg (DIC said 23.5 mpg) on the first tank. As for the AFM - I've never felt it - engage or disengage.

So, I'm curious since the salesman I talked to last night had no clue: Does the G8 GT run off of 87 octane or premium 91-93 (depending on where you live)? I have heard both, and was just curious to know before I actually pull the trigger on this car. Motor Trend says it runs on Premium, and I read somewhere else it runs on 87. I was hoping for an honest answer from someone

Runs on anything you put into it.

Personally i would like to know if you get 360hp on 87 or 93?

And if you get more HP for running 93

Yes you definately get more performance out of 93.. 93 with a tune nets big power over regular fuel.

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2007 Trailblazer SS Cammed!
2008 G8 GT Magnetic Grey Metallic #685

Thats what I was thinking. MT must have been running on Premium for their day of fun to milk all the extra power they could out of it

I am scared to look at the mpg's I am getting. I can't keep my foot out of it so I am sure it's not that great. LOL But hey, it's getting better than my lifted diesel. LOL

Have any proof of this happening?

What type of increase are we talking about?

361 on 93. SAE certification was done with premium, not regular. Same with EPA mileage run. But it will "dumb down" on lower grade and run without knocking.

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Hey guys, just joined.

First off I can wait to get my hands on a G8.

Second-from tuning on a WRX since 02, no crazy tuning wife has stingy pockets, higher octane doesn't necessarily make more power.

Higher ocate burns cleaner so that you can be more aggressive with your tuning without as much risk to the engine. I have seperate maps for 91 oct and 93 oct. Yes the 93 oct map makes more power but it runs a higher boost than the 91 oct which is where the power comes from.

I'm no expert but this is my understanding of it. Please if you agree or disagree let me know.

Thx

Jimmy

Higher octane allows higher compression or boost by reducing pre-ignition (knock), it does not burn hotter or cleaner than lower octane.
It's harder to ignite and so slows the flame front.
It does not contain more energy, it just lets you use the energy it contains safely in a higher compression or higher boost engine.

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Thx EB for the info

Does anyone know if the MPG we'll see with the G8 is worse with regular fuel??
Thx!

(edit - Sometimes I may want to use premium for performance, but for my wallet I'll probably want to use regular all the time unless it zaps fuel economy!)

For 2 or 3 bucks more, I'm running 93 all the time. It can only benefit UR G8GT.

ps I LOVE MY G8 GT

to be precise, higher octane fuel has a higher temperature flash point than lower octane fuel, which as stated above allows you to run more timing, comp ratio, or cylinder pressure (boost) with lowered risk of pre-ignition (knock or detonation)...

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Hamilton
-2002 Black Grand Prix GT

Given the 361hp rating of the small block V8 (which is 11hp above my humble C5's...) I would think, from what I've read elsewher, that all 361 ponies are availible WITH Premium. My C5 runs nothing but: best ever 25.1 Interstate, and yet still a touch over 22mpg driving "enthusiastically" on 2 lane mountain roller coasters in KY. If a G8 can do that....impressive. DFO

After a tune, I had the DOD extended by 7% throttle. I can not feel a difference driving on the highway and just got 26.4 mph averaging 76 on the turnpike.

This post is copied from another location. The testing was on a completely stock car with only the Roto-fab CAI added. I think a tune would only add to the gains!
I finally had the opportunity for a decent mileage test. My results were very positive. The trip was from SR 18/I-69 to Indianapolis via I-69 South to pick up my wife at the airport. I drove the first half of the trip with the stock air intake, then switched on the side of the road for the second half. The change only took about 8 minutes! The entire trip was interstate travel in the same direction, so wind, temp, etc. were very similar for both intakes. BTW, I did have a head wind for the entire trip, so mileage was probably a little low straight across the board. For each sample, I set the cruise control, reset the avg. speed/mpg, and tried to hold it for 4-5 miles. I scratched a couple samples where I encountered inclines and also scratched any samples where I had to disable the cruise control. A/C was off the entire time. I just filled up with 93 before leaving. Speeds weren't identical for my comparisons because the speedo didn't match the actual mph on the display or vice/versa.
Intake--------------avg speed/mph-----avg mpg

Stock--------------- 61.5-------------- 27
Roto-fab------------ 61.9-------------- 28.6----- +1.6

Stock--------------- 67.6-------------- 21.7
Roto-fab------------ 66.3-------------- 24.7----- +3.0

Stock--------------- 73.4-------------- 22.4
Roto-fab------------ 74.2-------------- 24.7----- +2.3

I didn't post 55-60 range because I was getting in traffic as I entered Indy. The Roto-fab intake was about 4-5 mpg better, but I think I had drafting help! I posted only three comparisons so that mph was similar for each; however, every single sample comparison netted a positive result for the Roto-fab intake.
Using round numbers, assuming $4/gal for 93, and an avg mpg of 25, here is what I would conclude:
The Roto-fab intake would increase gas mileage by an avg of at least 2 mpg. That means appr. $4 saved each 300 miles. x10=$40 for 3000 miles. x10 =$400 each 30,000 miles.
I wanted to do the same test on the way back, but years of experience as a husband told me to give my wife my undivided attention since I hadn't seen her in 2 weeks!
I posted this in response to a question. We realize some of you are looking for power and may not care about a gain in mileage if it means you have to keep your foot out of it! But virtually everyone hits the cruise control on a trip, so it's nice to know you can get some or all of your investment back when you aren't demanding performance from your G8.
We invite and encourage our customers to perform similar tests and post their results. My numbers were so good with our intake through the 55-61 mph range, I didn't even want to post them without another test! I think it would be great to hear some results from others anyway.

I picked my GT up in CT. on May 10th and have done nothing to it yet.
I just made a trip from North Carolina home to Connecticut.
I started the trip home with 2163 miles on it.
I filled up at Flying J in Fort Chiswell, VA with 87 octane.
I had already done 110 miles so the car was warmed up.

Running tire pressure was 39 front and 41 rear.
Ambient temperature during the drive was 70 - 74 degrees,
with low humidity and sunny skies.
A.C. was set to 72 degrees and on auto.
Put the car in drive and got onto I-81 N.

I pulled into the Flying J above Winchester, Va. 246.5 miles later.
DIC showed 68.1 avg. speed, 27.3 M.P.G. and 329 mile range remaining.
Tank took 8.792 gallons which calculates to 28.03 M.P.G.
I was very gentle on the throttle for this drive to see what I could
get for max mileage. Other than getting onto and off of the highway
I maintained my speed between 60 and 75 M.P.H.

Got back onto the highway and stopped 276.3 miles later at the
Valero station in Port Jervis, NY just off I-84 E.
DIC showed 67.8 avg. speed, 25.0 M.P.G. and 271 mile range remaining.
Tank took 10.802 gallons which calculates to 25.57 M.P.G.
This tank I drove normally, which means more throttle, but nothing crazy.

I am quite happy with the mileage I am getting.
Most of my driving is highway. My city driving is really mostly rural roads;
not real stop and go type city. The first couple of tanks of gas were a
variety of driving and I averaged between 19.5 and 22 so I am happy with
that also.

I'm getting 21.7 MPG (DIC) doing mainly back-road driving with some highway. It's been years since I bothered checking the computer. I think I can tell when the AFM is active, but it is quite subtle (and I could be wrong ). I only have around 450 miles so I'm still not really doing any 'spirited' driving yet. I'm trying to be good and break-in the engine "by the book".

the computer was programed for 87....so you're wasting money if you use 90+ octane.

I have 1400 miles of 95% city driving and at this time I'm getting 16.3 MPG. That's better than the truck I traded for the G8. I can be heavy on the gas at times but I don't beat the car often. Some day I will do some Highway driving and see what I get then.

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Blk 2008 G8 GT
Blue 2001 Mustang GT Bullitt