sorry if this has been asked anyone know if the G8 GT will have to run 91 Octane or will it be able to run on 87?

It will run on 87 octane.

nice! that sweetens the deal even more

sorry if this has been asked anyone know if the G8 GT will have to run 91 Octane or will it be able to run on 87?
We are hoping a tune for 92 and a CAI will get this pup to 400+ HP.

that would be sweet

i know teh tune for 93 and cai on my 07 Mustang really woke it up. SCT rocks

I think 380 would be more realistic.

Tune and CAI will be well over 400 crank horsepower, its an LS2 lower end (sorf of ;)) with L92 heads and LS3 intake LOL

Tune and CAI will be well over 400 crank horsepower, its an LS2 lower end (sorf of ;)) with L92 heads and LS3 intake LOL
Outstanding!:bubbrubb:

:hail: = Chris White

Tune and CAI will be well over 400 crank horsepower, its an LS2 lower end (sorf of ;)) with L92 heads and LS3 intake LOL

Probably on par with what GTO owners are seeing with L92 head/L76 intake swaps. Is it possible to see another 50hp from the right cam to go with a tune?

cai + cam + tune = Joy

What do you think the real-world mileage will be?

sorry if this has been asked anyone know if the G8 GT will have to run 91 Octane or will it be able to run on 87?

GM Powertrain calls for Premium.


2008 "L76" 6.0L V8 ( L76 ) 101707
Type: 6.0L Gen IV V8 Small Block
Displacement: 5967cc (364 ci)
Compression ratio: 10.4:1
Valve configuration: overhead valves (2 valves per cylinder)
Assembly site: Silao
Valve lifters: hydraulic roller
Firing order: 1 - 8 - 7 - 2 - 6 - 5 - 4 - 3
Bore x stroke: 101.6 x 92mm
Fuel system: sequential fuel injection ( SFI )
Fuel type: premium recommended
Fuel shut off: 6000 RPM
Emissions controls: catalytic converter
three-way catalyst
positive crankcase ventilation
Engine Orientation Longitudinal
Valves per cylinder 2
Bore Center (mm) 111.76
Engine Mass TBD
Applications: Horsepower: hp ( kw )
Pontiac G8 GT 361 hp ( 268 kW ) @ 5300 rpm SAE CERTIFIED
Applications: Torque: lb-ft. ( Nm )
Pontiac G8 GT 385 lb-ft ( 520 Nm ) @ 4400 rpm SAE CERTIFIED
MATERIALS
Block: cast aluminum
Cylinder head: cast aluminum
Intake manifold: composite
Exhaust manifold: cast nodular iron
Main bearing caps: powder metal
Crankshaft: cast nodular iron with undercut and rolled fillets
Camshaft: hollow steel
Connecting rods: powder metal
Additional features: extended life spark plugs
extended life coolant
Active Fuel ManagementTM
Oil Life System
electronic throttle control
extended life accessory drive belt

Probably on par with what GTO owners are seeing with L92 head/L76 intake swaps. Is it possible to see another 50hp from the right cam to go with a tune?

Tune and CAI will be well over 400 crank horsepower, its an LS2 lower end (sorf of ;)) with L92 heads and LS3 intake LOL

The L76 is a better engine than the LS2 except the AFM spec cam has reduced lift on the four deact cylinders. So I have to believe that a big bump in power will require a cam and a (non-AFM) tune.

Of course the better heads and intake mean you will probably get more power than an LS2 if you just install an LS2 cam and stock LS2 tune. And if you going to bother, might as well go a little hotter than LS2 stock...

Upon email through Pontiac's website, I was told the engine ratings were on 87.

Why do the AFM cylinders get less lift?

Upon email through Pontiac's website, I was told the engine ratings were on 87.

Why do the AFM cylinders get less lift?

You were told wrong.



The above post is straight from the GM Powertrain.com site for the 2008 L76 engine section. The SAE ratings are on Premium, not 87.

This is from the 2008 Fuel Economy Guide.
The P stands for Premium.

A-5 5.7/8 15/22 $2,594
FORD
Crown Victoria FFV A-4 4.6/8 15/23 $2,594 Gas
11/16 $2,768 E85
Taurus AWD A-6 3.5/6 17/24 $2,454
Taurus FWD A-6 3.5/6 18/28 $2,123
HONDA
Accord A-5 2.4/4 21/31 $1,945
Accord M-5 2.4/4 22/31 $1,866
A-5 3.5/6 19/29 $2,123
HYUNDAI
Azera A-5 3.3/6 18/26 $2,221
A-5 3.8/6 17/26 $2,333
Sonata A-4 2.4/4 21/30 $1,945
M-5 2.4/4 21/31 $1,866
A-5 3.3/6 19/28 $2,123
INFINITI
M35 A-S5 3.5/6 16/23 $2,635 P
M35x A-S5 3.5/6 16/22 $2,786 P
M45 A-S5 4.5/8 16/21 $2,786 P
M45x A-S5 4.5/8 14/20 $3,131 P Tax
JAGUAR
Super V8 A-6 4.2/8 15/22 $2,786 P S
Vdp Lwb A-6 4.2/8 16/25 $2,635 P
XJ8 A-6 4.2/8 16/25 $2,635 P
XJ8L A-6 4.2/8 16/25 $2,635 P
XJR A-6 4.2/8 15/22 $2,786 P S
KIA
Amanti A-5 3.8/6 17/24 $2,454
LINCOLN
Town Car A-4 4.6/8 15/22 $2,594
Town Car FFV A-4 4.6/8 15/23 $2,594 Gas
11/16 $2,768 E85
MASERATI
Quattroporte A-6 4.2/8 12/18 $3,577 P Tax
MAYBACH
57 A-5 5.5/12 10/16 $4,173 P T Tax
57S A-5 6.0/12 10/16 $4,173 P T Tax
62 A-5 5.5/12 10/16 $4,173 P T Tax
62S A-5 6.0/12 10/16 $4,173 P T Tax
MERCEDES-BENZ
S550 A-7 5.5/8 14/21 $3,131 P Tax
S550 4matic A-7 5.5/8 14/20 $3,131 P Tax
S600 A-5 5.5/12 11/17 $3,853 P T Tax
S63 AMG A-S7 6.2/8 11/17 $3,853 P Tax
S65 AMG A-S5 6.0/12 11/17 $3,853 P T Tax
Trans Type/
Speeds
Eng Size /
Cylinders
MPG
City / Hwy
Annual Fuel
Cost
Notes
MERCURY
Grand Marquis FFV A-4 4.6/8 15/23 $2,594 Gas
11/16 $2,768 E85
Sable AWD A-6 3.5/6 17/24 $2,454
Sable FWD A-6 3.5/6 18/28 $2,123
PONTIAC
G8 A-S6 6.0/8 15/24 $2,786 P
TOYOTA
Avalon A-S6 3.5/6 19/28 $2,123
SMALL STATION WAGONS
AUDI
A3 A-S6 2.0/4 22/29 $2,004 P T
M-6 2.0/4 21/29 $2,089 P T
A3 Quattro A-S6 3.2/6 18/25 $2,385 P
A4 Avant Quattro A-S6 2.0/4 19/27 $2,280 P T
M-6 2.0/4 20/28 $2,179 P T
A-S6 3.1/6 17/25 $2,505 P
M-6 3.1/6 15/25 $2,635 P
S4 Avant A-S6 4.2/8 14/21 $3,131 P Tax
M-6 4.2/8 13/20 $3,342 P Tax
BMW
328i Sport Wagon A-S6 3.0/6 18/27 $2,385 P
M-6 3.0/6 17/27 $2,505 P
328xi Sport Wagon A-S6 3.0/6 17/25 $2,505 P
M-6 3.0/6 17/25 $2,505 P
HONDA
Fit A-S5 1.5/4 27/33 $1,609
Fit A-5 1.5/4 27/34 $1,553
Fit M-5 1.5/4 28/34 $1,507
PONTIAC
Vibe A-4 1.8/4 25/31 $1,726
M-5 1.8/4 26/33 $1,609
SAAB
9-3 SportCombi A-S5 2.0/4 18/24 $2,505 P T
M-6 2.0/4 19/29 $2,179 P T
A-S6 2.8/6 15/24 $2,786 P T
M-6 2.8/6 16/26 $2,635 P T
SCION
xB A-S4 2.4/4 22/28 $1,945
M-5 2.4/4 22/28 $1,945
SUBARU
Impreza Wagon/Outback
SPT AWD A-S4 2.5/4 20/25 $2,280 P T
A-S4 2.5/4 20/27 $2,123
M-5 2.5/4 20/27 $2,123
M-5 2.5/4 19/25 $2,385 P T
M-6 2.5/4 17/23 $2,635 P T
12 WWW.FUELECONOMY.GOV

Holy superfluous information...

I'll look into it.

Interesting and disappointing because now with the higher octane rating a tune will produce less of gain in HP. Does anyone know what type of material the pistons are made of in the L76 will have. Just curious since I know some will place the motor under boost:D

Chris,
Does that mean that the EPA fuel economy book is a typo also?

Thats good news, thanks for clarifying.

No sweat, everyones been saying that all along anyhow :)

So, Chris, when are you gonna get a spin in the new ZR1? :burnout:

So, Chris, when are you gonna get a spin in the new ZR1? :burnout:

I've been in a mule, not a production car though ;) Close enough for me :D

The L76 is a better engine than the LS2 except the AFM spec cam has reduced lift on the four deact cylinders. So I have to believe that a big bump in power will require a cam and a (non-AFM) tune.

Of course the better heads and intake mean you will probably get more power than an LS2 if you just install an LS2 cam and stock LS2 tune. And if you going to bother, might as well go a little hotter than LS2 stock...

What are the stock cam specs for the L76? This is the opposite of the cam for the 5.3 AFM engine. It has slightly more lift on the deact cylinders, like it is compensating in some way.

Thanks,

Chip

I've been in a mule, not a production car though ;) Close enough for me :D

God you suck. :fawkdance: I haven't even ridden in a vette since '99.

Also something to make it easier to grasp as far as power vs octane goes, the L76 truck motor albeit with VVT makes 366 horsepower on 87 octane and thats with the crappy truck intake :D

PMD you NEED to get into a C6, they are amazing!

Still a bit confused... the epa site says Premium gas is required for the GT. But i swear the pontiac website says regular and this was one of the selling points...

So which is it?

i mean taken from www.gmhightechperformance.com/features/0707gm_pontiac_g8/index.html it says
"Speaking of fuel, the L76 in the G8 is calibrated to unleash an astounding 362 hp on regular fuel. This is a dream come true for tuners, who will likely be able to wring over 40 hp by simply tweaking the fueling and spark to use high-test premium gasoline. Tuning, of course, leads us to another topic: the engine controller. As of press time, it appears the G8 will be sporting the relatively new Delphi E67 controller. This faster processor allows control of the Displacement on Demand and cam-phasing (if equipped) simultaneously, and adds a few needed input and output drivers, as well."

I asked through the website again, citing what I was told before and that GM Powertrain says premium. And they told me again that the recommended fuel is Regular.

Also something to make it easier to grasp as far as power vs octane goes, the L76 truck motor albeit with VVT makes 366 horsepower on 87 octane and thats with the crappy truck intake :D

PMD you NEED to get into a C6, they are amazing!

I drove by the local Chevy dealership this weekend, they had a Jetstream Blue Z06 sitting out front. :yumyum: I know one of the salesmen there pretty well, I'm going to see if he'll at least let me sit in it and ask if they will sell it for sticker. :gr_jest: They do have a used C6 on the lot, I might see if he'll let me take it for a spin.

I've been in a mule, not a production car though ;) Close enough for me :D

Like PMD said, you suck. I remember reading your article on the Z06 when it first came out. Since the ZR1 is 6 months or so away from being sold, I figured you would have been forced to review one.

one of the huge attractions to this car is the regular unleaded tag.

I hope that the EPA website is wrong and the website info they are posting is correct.


Lets hope its not
Pontiac G8 regular unleaded
Pontiac G8 GT premium unleaded

If the official Pontiac site says 87 unleaded for the L76, then its 87 unleaded. Afterall, I'm sure they'd be willing to buy you premium for as long as you own your G8 GT if they are wrong!!

What about us mountain state drivers. We get 85 Octane, how do you think that will affect the G8s?

Same way it affects all other cars requiring 87 octane fuel?

What about us mountain state drivers. We get 85 Octane, how do you think that will affect the G8s?

If that is "low grade", wouldn't there be an option for 87-89 octane as "mid grade"?

I would think the gas stations in the mountain areas would offer three grades of gasoline, just like all the rest of the country. If the "low" grade doesn't have enough octane, move up to the "mid" grade!?! Maybe a few extra $$ per tankfull, but the car will run better so..........:boink:

Our gas around here is now about $2.85 for regular unleaded and 3.10 for premium unleaded...@ 20,000 mile a year and say an average 20 MPG on a tank....you are talking a difference of only $250 a year or call it $20 a month give or take....and you are buying a $30,000 car...if the $20-30 a month hurts, please do not look at the cost of depreciation..

our grades are 85, 89, 91. now the interesting thing is that my 2004 GP runs better on the 85 going up the mountain passes than the 87 that i had in the car when I came out to Utah.

Received in an e-mail.

Thank you for contacting Pontiac and your interest in the 2008 G8! We appreciate the time you have taken to write us.

Below, we have provided an excerpt from the G8 owner’s manual pertaining to gasoline octane. Please be advised that any deviation from the instructions provided by the owner’s manual may result in damages which would not be covered by the new vehicle warranty. Also, we are unable to provide fuel mileage estimates for vehicles using gasoline other than the recommended octane. We apologize for any inconvenience.

"If your vehicle has a V8 engine, use regular unleaded gasoline with a posted octane rating of 87 or higher. If the octane rating is less than 87, you might notice an audible knocking noise when you drive, commonly referred to as spark knock. If this occurs, use a gasoline rated at 87 octane or higher as soon as possible. If you are using gasoline rated at 87 octane or higher and you hear heavy knocking, the engine needs service.

If your vehicle has the 3.6L V6 engine (VIN Code 7), use regular unleaded gasoline with a posted octane rating of 87 or higher. For best performance or trailer towing, you could choose to use middle grade 89 octane unleaded gasoline. If the octane rating is less than 87, you might notice an audible knocking noise when you drive, commonly referred to as spark knock."

At Pontiac, we strive to provide exceptional customer service. If we can be of any further assistance please email us or call 1-800-762-2737, between 8:00 a.m. and 11:00 p.m., Eastern Time, seven days a week. Thank you for contacting Pontiac!

Sincerely,

The Pontiac Marketing Team
http://www.pontiac.com/

so 87 it is!

so 87 it is!

Yeah, kinda like the regular unleaded, that some of us said was the fuel of choice, way back when all this discussion started.:boink:

The G8 owner’s manual quote does not address changes in octane requirement related to changes in altitude. Because there is less air at higher altitude, there is less absolute compression and as a result, octane ratings can be less without pre-detonation. Fuel sold at higher altitudes i.e. most of Utah, is nearly always lower octane in all grades.

Our gas around here is now about $2.85 for regular unleaded and 3.10 for premium unleaded...@ 20,000 mile a year and say an average 20 MPG on a tank....you are talking a difference of only $250 a year or call it $20 a month give or take....and you are buying a $30,000 car...if the $20-30 a month hurts, please do not look at the cost of depreciation..

At Todays Prices

Regular Unleaded - $2.79
Super/Supreme Unleader $3.11

Difference of .32cents

If your vehicel has a 19 Gallon Tank your

Avg cost difference per fillup 19 x.32 = $6.08

25 mpg avg = (25x19=475) miles between fillups

@ 56 miles a day on average (475/56=8.5)

Every 8.5 days we would need a fillup

At 8.5 days that would be 43x times in a year

Let's assume gas prices in that year remain constant and does not go up and you do not drive anywhere on the weekends.

43*6.08 = 261.00 would be your minimum savings in gas.

Given that this could go up or down depending on how many miles you drive in the weekend.

Worst Case

Difference of .35 a gallon
.35*19= 6.65

@60 miles per day on average (475/60=)

Every 7.91 days we would need a fillup

At 7.91 days that would be 46x times in a year
46*6.65 305 bucks in savings.

well from beign a college student working part time that extra 6 bucks a fill up is a lot!

well from beign a college student working part time that extra 6 bucks a fill up is a lot!

If the $6/fillup is a lot, perhaps you should rethink whether you can afford this car in the first place! There are a lot of other costs that are considerably more, tires(proper set @ $750-$1000), oil changes (Mobile 1 will probably be the recommended oil @ $6+/quart), normal routine service $65-100 every 3-6 months, etc, etc. Not to mention the insurance man will want a hefty check, especially if you are under 25! So the cost of a fillup is pretty much a minor issue, everything considered!:eek2:

Good to see Regular. Those that want premium can do the tune and have at it. This will be a family car for me to haul my wife and grandson around when we can get him! (hard right now since my son is in the Navy stationed at Pearl Harbor!) But soon, gotta have a 4 door and the GT G8 fits the bill, I think. Can't wait to see one, was looking at the Malibu - nice ride, wish they offered an SS model.

If the $6/fillup is a lot, perhaps you should rethink whether you can afford this car in the first place! There are a lot of other costs that are considerably more, tires(proper set @ $750-$1000), oil changes (Mobile 1 will probably be the recommended oil @ $6+/quart), normal routine service $65-100 every 3-6 months, etc, etc. Not to mention the insurance man will want a hefty check, especially if you are under 25! So the cost of a fillup is pretty much a minor issue, everything considered!:eek2:

I wouldn't think that Mobil 1 would be required. I would recommend it, but if it doesn't leave the factory with M1, you wouldn't be required to run it. The only other problem with his insurance would be if he's under 25. I got my GTO when I was 27. I had a driving record that averaged a speeding ticket each year. My insurance company (not a big national company) only charged me less than $500 for 6 month increments. Perhaps that's my advantage. But, if his current insurance company dumps an unreasonable estimate for insurance, he should shop around. Don't get just cheap insurance. Make sure they will offer the best policy for the money. The G8 should be less expensive because it's a sedan (not a sport coupe), has ABS, airbags (more than the GTO), traction control, & Stabilitrak. The more safety features the car has, the insurance company will think he is buying a car that will help him avoid an accident.

If the $6/fillup is a lot, perhaps you should rethink whether you can afford this car in the first place! There are a lot of other costs that are considerably more, tires(proper set @ $750-$1000), oil changes (Mobile 1 will probably be the recommended oil @ $6+/quart), normal routine service $65-100 every 3-6 months, etc, etc. Not to mention the insurance man will want a hefty check, especially if you are under 25! So the cost of a fillup is pretty much a minor issue, everything considered!:eek2:

ive had two V-8 mustnags since iwas 16. an 04 GT and now an 07 GT. i can afford this car. all im sayin was if it was gonna cost me 40 bucks to fill up versus 46 and i fill up every 5-6 days id rather pay the 40 then the 46.

I've been putting the "good stuff" in the GTO. There are a few places in town where it is $.10 a gallon more. Brown bag it to work one day and you're even.

I do look forward not having to do that though.

hahaha. yea when i had the DIablo Tune in my 04 i had to run premium in it, and that was devoting almost my enitre paycheck to gas. then again i had a crappy job at the time

I've been putting the "good stuff" in the GTO. There are a few places in town where it is $.10 a gallon more. Brown bag it to work one day and you're even.

I do look forward not having to do that though.

I remember when it was a dime between fuel grades. Now, oil companies are stretching prices a few more pennies so that the difference between cheap **** & premium is a quarter. :mad:

by me its almost 30 cents difference.

So what I would like to know is if the 362hp rating is on 87 octane or 91+ octane. I always thought it was on 87 but I keep reading conflicting information.

I am gonna guess they used premium to bump up the EPA mileage ratings...

I believe the HP rating is on 87 Octane...

GM Powertrain says Premium.

GM Powertrain calls for Premium.


2008 "L76" 6.0L V8 ( L76 ) 101707
Type: 6.0L Gen IV V8 Small Block
Displacement: 5967cc (364 ci)
Compression ratio: 10.4:1
Valve configuration: overhead valves (2 valves per cylinder)
Assembly site: Silao
Valve lifters: hydraulic roller
Firing order: 1 - 8 - 7 - 2 - 6 - 5 - 4 - 3
Bore x stroke: 101.6 x 92mm
Fuel system: sequential fuel injection ( SFI )
Fuel type: premium recommended
Fuel shut off: 6000 RPM
Emissions controls: catalytic converter
three-way catalyst
positive crankcase ventilation
Engine Orientation Longitudinal
Valves per cylinder 2
Bore Center (mm) 111.76
Engine Mass TBD
Applications: Horsepower: hp ( kw )
Pontiac G8 GT 361 hp ( 268 kW ) @ 5300 rpm SAE CERTIFIED
Applications: Torque: lb-ft. ( Nm )
Pontiac G8 GT 385 lb-ft ( 520 Nm ) @ 4400 rpm SAE CERTIFIED
MATERIALS
Block: cast aluminum
Cylinder head: cast aluminum
Intake manifold: composite
Exhaust manifold: cast nodular iron
Main bearing caps: powder metal
Crankshaft: cast nodular iron with undercut and rolled fillets
Camshaft: hollow steel
Connecting rods: powder metal
Additional features: extended life spark plugs
extended life coolant
Active Fuel ManagementTM
Oil Life System
electronic throttle control
extended life accessory drive belt

From what I have read 87 octane it is, http://autos.aol.com/cars-Pontiac-G8-2008/overview

its probably one of those it can run 87 wiht no problems but best performance use 93

Post # 40 seems to settle the issue...hp/tq and epa mpg have to be in line with owners manual of reg unleaded...my post #38 was made when it was not clear...trust me I too am glad it it regular...

My wrench friends recommend chevron because of the techron..but any top level gas should be good for a cleaner engine..

well the motor trend review says premium

The motor trend review say's recomended premium. The bottom line is the car will run regular just fine. However premium is recmended for performance driving which is what a vehicle review generally is. as for all the other I would trust Chris more than other sources on the net. He's always been a great guy and never led me wrong (well there was that intense thing wasn't there lol).

I am hoping the get the wife a G8 at some point. We're running a little short on pontiacs around here since my goat was totaled!

The operative word is "recommended", not "required." My GTO says "required." My GTP says "recommended." Run regular and the timing is retarded under load which robs you of some horsepower, but it won't harm the engine.

I would think Mobil 1 would be a better choice for the 6.0L mill, as it is required (not just recommended) in the LS2 in my GTO. I'll run it in my G8 GT if I can get one.

I find that most 87 octane is crap anymore. Especially if 10% ethanol is required to get it to 87 octane... they must start out with some pretty low grade gas. I'll use it for the old lawnmower, but that's about it.

i don't care what others saying.

everything i have owned i always put 93 in them. so G8 will have 93 in it as well

i don't care what others saying.

everything i have owned i always put 93 in them. so G8 will have 93 in it as well

You know things that arent tuned for 93 octane will get less fuel economy and power on 93 VS the correct fuel its tuned for?

You know things that arent tuned for 93 octane will get less fuel economy and power on 93 VS the correct fuel its tuned for?

Depends on the compression ratio and the timing and tuning. On low compression engines, that's true. My GTP will run on regular, but premium is "recommended" for it. The computer compensates by limiting supercharger boost and retarding timing to control pre-ignition. You can definitely tell the difference in performance when you run a tank of the cheap stuff in it. How this will affect the G8GT is unknown so far. If you have the timing and compression to handle higher octane but back off timing to eliminate knock, you aren't gaining anything with regular (except price), but you could be sacrificing power.

It's not unknown I've tuned G8's LOL And a vehicle tuned to run 87 will get worse mileage and power on 93 just like I said above ;) There is no reason to run 93 in anything unless its tuned for it, which the G8GT isnt fully.

You want to run the fastest burning gas you can without pre ignition, and if its not tuned for 93 its not going to do anything but cost more ;)

GTP's were tuned to run on premium so thats a no brainer and not really a revelvant example here. I see where you say it depends on the tuning well thats exactly what I said, if its tuned for 87 its not going to do anything :D

It's not unknown I've tuned G8's LOL And a vehicle tuned to run 87 will get worse mileage and power on 93 just like I said above ;) There is no reason to run 93 in anything unless its tuned for it, which the G8GT isnt fully.

You want to run the fastest burning gas you can without pre ignition, and if its not tuned for 93 its not going to do anything but cost more ;)

GTP's were tuned to run on premium so thats a no brainer ;)

I agree. Some of us need the mpg on regular gas. I need a bigger car, don't want to give up sporty, but have to be practical to a certain amount. Regular gas and 8 to 4 when cruising fill this bill for me. Got to save as much as I can and running regular helps immensely over the price of high test at today's prices...not to mention the future! I figure I have to look at it like the money I get for selling the Honda (30city/40hwy on reg) will go a long way in buying gas for the G8! Can't give up the V8 though!

It's not unknown I've tuned G8's LOL And a vehicle tuned to run 87 will get worse mileage and power on 93 just like I said above ;) There is no reason to run 93 in anything unless its tuned for it, which the G8GT isnt fully.

You want to run the fastest burning gas you can without pre ignition, and if its not tuned for 93 its not going to do anything but cost more ;)

GTP's were tuned to run on premium so thats a no brainer and not really a revelvant example here. I see where you say it depends on the tuning well thats exactly what I said, if its tuned for 87 its not going to do anything :D

I think we're on the same page here. However IF Pontiac is saying that premium may enhance performance (their words apparently from another post -- I have no literature on it), then it is possible that the engine can benefit from higher octane fuel. The GTP, by using a computer-controlled boost waste gate, in effect dynamically modifies its own compression ratio (and it's a very low 7:1 if I recall w/o the 'charger boost). Ignition timing is used in much the same way to control pre-ignition with low grade fuel. The question is (and I haven't seen any engine specs) does the L76 have sufficient compression to effectively use premium if it is there, or is it low enough that it would be of no benefit. The low/high octane question becomes blurred with increasing engine/computer controls, and the "tuning" becomes somewhat a function of dynamic computer controls rather than hardwired programming. I'd like to see the compression ratios, which would be a better indicator of the ability to use premium effectively. In mine, since the wife's going to be hauling groceries with it, I'll burn regular.

GTP's CR is 8.5:1 ;) CR has nothing to do with it once its tuned though, if its tuned to NOT ping on regular its not going to help :) Can it burn 93 with a 93 tune? Sure it'll help alot but GM vehicles dont ramp up timing on thier own over the high octane table so if its tuned for 87-89 in the high octane table thats the best they are going to get ;)

Not sure I want to push this further, but.... High octane fuel burns more slowly than lower octane, obviously. Slower burning is an advantage because it reduces pre-ignition and allows a long, strong power stroke (rather than a bang and a whimper) :D. But high octane is a disadvantge if the engine compression is insufficient to completely ignite the entire air/fuel mix before the end of the effective power stroke. Higher compression generates more heat, causing low octane fuel to burn before the power stroke is completed, and it also creates a pre-mature ignition during intake before the power stroke because of the higher heat caused by higher compression (PV=nRT and Engine 101). You reduce pre-ignition by lowering compression, using knock sensors (and the 6Ls have several), retarding ignition timing (delayed spark), and using high octane fuel. So, if the "detuning" of the GT is handled, in part, by computer control (as it must be), it is only reasonable to assume that the controllable parameters (ignition timing) are constantly being adjusted, and that there is headroom both above AND below optimum settings. With no boost, compression ratios are set in stone (unless you play with the heads), so this is not a variable in the G8. But my point is that, given sufficient compression ratios (and I plead innocence here because I just don't know), it could adequately manage low octane fuel by computer control, yet provide for adjustment for higher octane, hence the "enhanced performance" quote from elsewhere. That is the only reason I question the ability to use higher octane. That is an unusual comment, coming from the factory and raises some speculation. There is no disagreement that an engine designed only for regular will not benefit from premium.

Does anyone know where the information came from about the GT having possibly enhanced performance with premium? One way that would be true is with sufficient compression to handle high octane fuel when it is used.

Not sure I want to push this further, but.... High octane fuel burns more slowly than lower octane, obviously. Slower burning is an advantage because it reduces pre-ignition and allows a long, strong power stroke (rather than a bang and a whimper) :D. But high octane is a disadvantge if the engine compression is insufficient to completely ignite the entire air/fuel mix before the end of the effective power stroke. Higher compression generates more heat, causing low octane fuel to burn before the power stroke is completed, and it also creates a pre-mature ignition during intake before the power stroke because of the higher heat caused by higher compression (PV=nRT and Engine 101). You reduce pre-ignition by lowering compression, using knock sensors (and the 6Ls have several), retarding ignition timing (delayed spark), and using high octane fuel. So, if the "detuning" of the GT is handled, in part, by computer control (as it must be), it is only reasonable to assume that the controllable parameters (ignition timing) are constantly being adjusted, and that there is headroom both above AND below optimum settings. With no boost, compression ratios are set in stone (unless you play with the heads), so this is not a variable in the G8. But my point is that, given sufficient compression ratios (and I plead innocence here because I just don't know), it could adequately manage low octane fuel by computer control, yet provide for adjustment for higher octane, hence the "enhanced performance" quote from elsewhere. That is the only reason I question the ability to use higher octane. That is an unusual comment, coming from the factory and raises some speculation. There is no disagreement that an engine designed only for regular will not benefit from premium.

Does anyone know where the information came from about the GT having possibly enhanced performance with premium? One way that would be true is with sufficient compression to handle high octane fuel when it is used.

Did you read GTPrix's post? CR does not matter. GTPrix works for GM. If anybody would know how the computer works on this site it would be him.

IF the PCM can learn the higher octane... how often is it advancing timing to induce knock? I question an engine's durability when the computer is constantly knocking on purpose. It's that reason that makes me think if the manufacturer says regular, I'm gonna run regular.

That... and higher octane fuel has less internal energy than lower octane, which is why you want to run the lowest octane you can at a certain set of parameters.

And yeah, my Bonny came tuned for 91 and I had it retuned for 93.

Not sure I want to push this further, but.... High octane fuel burns more slowly than lower octane, obviously. Slower burning is an advantage because it reduces pre-ignition and allows a long, strong power stroke (rather than a bang and a whimper) :D. But high octane is a disadvantge if the engine compression is insufficient to completely ignite the entire air/fuel mix before the end of the effective power stroke. Higher compression generates more heat, causing low octane fuel to burn before the power stroke is completed, and it also creates a pre-mature ignition during intake before the power stroke because of the higher heat caused by higher compression (PV=nRT and Engine 101). You reduce pre-ignition by lowering compression, using knock sensors (and the 6Ls have several), retarding ignition timing (delayed spark), and using high octane fuel. So, if the "detuning" of the GT is handled, in part, by computer control (as it must be), it is only reasonable to assume that the controllable parameters (ignition timing) are constantly being adjusted, and that there is headroom both above AND below optimum settings. With no boost, compression ratios are set in stone (unless you play with the heads), so this is not a variable in the G8. But my point is that, given sufficient compression ratios (and I plead innocence here because I just don't know), it could adequately manage low octane fuel by computer control, yet provide for adjustment for higher octane, hence the "enhanced performance" quote from elsewhere. That is the only reason I question the ability to use higher octane. That is an unusual comment, coming from the factory and raises some speculation. There is no disagreement that an engine designed only for regular will not benefit from premium.

Does anyone know where the information came from about the GT having possibly enhanced performance with premium? One way that would be true is with sufficient compression to handle high octane fuel when it is used.


Uhh... yeah I'm going to stop now it's clear after the first sentence how this is going to end ROFL

IF the PCM can learn the higher octane... how often is it advancing timing to induce knock? I question an engine's durability when the computer is constantly knocking on purpose. It's that reason that makes me think if the manufacturer says regular, I'm gonna run regular.

That... and higher octane fuel has less internal energy than lower octane, which is why you want to run the lowest octane you can at a certain set of parameters.

And yeah, my Bonny came tuned for 91 and I had it retuned for 93.

Thank God, someone who understands! To recap (and answer your question) if the high octane table is tuned for 87-89 the ECM will NOT add timing over that so putting in 93 in a vehicle tuned for 87-89 has NO benefit other than less power and degraded fuel economy.

The inverse however is true if you put 87 in a vehicle tuned for 93 and beat on it, it'll knock itself right into the low octane table which is tuned for like 84 octane (IE water LOL)

IF the PCM can learn the higher octane... how often is it advancing timing to induce knock? I question an engine's durability when the computer is constantly knocking on purpose. It's that reason that makes me think if the manufacturer says regular, I'm gonna run regular.

That... and higher octane fuel has less internal energy than lower octane, which is why you want to run the lowest octane you can at a certain set of parameters.

And yeah, my Bonny came tuned for 91 and I had it retuned for 93.

The only way it can learn a higher octane is with a computer and a tuner retuning it. It isn't capable of advancing the timing. It can only retard it. I guess if it sees bad gas and it retards the timing, then gets good gas, does it advance it or return it to normal?

The only way it can learn a higher octane is with a computer and a tuner retuning it. It isn't capable of advancing the timing. It can only retard it. I guess if it sees bad gas and it retards the timing, then gets good gas, does it advance it or return it to normal?

After a certain amount of drive cycles and low knock sensor activity the ECM will slowly ramp the timing back in to full timing in the high octane table. Nothing more, so again if its tuned for 87-89 its not going any higher ;)

The only way it can learn a higher octane is with a computer and a tuner retuning it. It isn't capable of advancing the timing. It can only retard it.

OK, I'm outta this one. Two parting comments:

I wasn't aware that ECM programming only went one way -- doesn't make sense, nor is it difficult to program. But if that's true, then I agree premium is a waste. Still makes me wonder about the statement about "enhanced performance" from Pontiac. I rest my case.

Second, compression does matter. If you run regular in an 11:1 CR engine (all else equal -- no fancy computer compensation), it will knock. If you run it in a 9:1 compression engine, it will not knock. Basic physics. Volume is inversely proportional to pressure. Temperature is directly proportional to pressure. Raise CR, you decrease volume and raise temperature. Since no one knows the programming parameters of GM's ECMs, are we assuming they cannot compensate for "better" fuel, or do we know that for a fact. If the CR is low, then it doesn't matter. If it is sufficient high to handle premium but the ECM backs things down to prevent pre-ignition, then premium may be an option for the so-called "enhanced performance."

Another incorrect fact is that premium fuel has less internal energy than regular. Just the opposite. Longer hydrocarbon chains contain more energy than shorter ones. A good example of this is the loss in fuel economy with ethanol blends and E85 fuels, and the fact that alcohols burn with less heat than gasoline.

Another incorrect fact is that premium fuel has less internal energy than regular. Just the opposite. Longer hydrocarbon chains contain more energy than shorter ones. A good example of this is the loss in fuel economy with ethanol blends and E85 fuels, and the fact that alcohols burn with less heat than gasoline.


Ethanol is used to increase octane, and you say it burns cooler, but since it increases octane, it has higher energy?:confused: E85 gets lower economy because it has lower internal energy than gasoline.

Higher octane fuel has less internal energy. I don't wanna sound like a jerk... but I'm right. I learned all the chemistry in college, and other than people on forums that don't know, the internet agrees. It's a main reason why they still make "regular" instead of tuning everything for higher octane.

Ethanol is used to increase octane, and you say it burns cooler, but since it increases octane, it has higher energy?:confused: E85 gets lower economy because it has lower internal energy than gasoline.

Higher octane fuel has less internal energy. I don't wanna sound like a jerk... but I'm right. I learned all the chemistry in college, and other than people on forums that don't know, the internet agrees. It's a main reason why they still make "regular" instead of tuning everything for higher octane.

Well, I can't leave yet, I guess. You are confusing octane rating with potential energy. Octane rating has no direct relation to the energy content of the fuel. It is a measure of the tendency to spontaneously ignite, and is based on an arbitrary number 100 which is the autoignition tendency of 2,2,4-trimethylpentane (isooctane), by definition. Chemicals such as methyl tertiary butyl ether (MTBE) and tetraethyl lead were used in the past to increase octane ratings in trace amounts due to their inhibiting effects, not their own inherent octane rating or potential energy -- sort of like a reverse catalyst.

It is true that ethanol has a higher octane rating than regular gasoline, and it's "cleaner" than MTBE or TEL, hence its use. Ethanol does, in fact, have less potential energy than n-octane. You can look this up in a Merck manual in your chemistry department. It effectively changes (raises) the "effective" octane rating of gasoline both by its own higher octane rating and by its cooling effect.

The use of regular gasoline is an economic issue. Smaller chain hydrocarbons typical of regular gasoline mixtures are cheaper to refine than premium (higher carbon chain lengths), thus the higher price of higher octane fuel. Higher octane is desirable when you're building a performance engine, trying to squeeze all the energy from the fuel you can by packing the cylinder tighter (higher compression), generating more heat leading to pre-ignition.

As stated above, Motor Trend says premium is recommended. Do they know, or are they guessing? They also give CR as 10.4:1 which is fairly high for regular.

Oh, yes. If you'll check my user CP, you'll see I'm a chemist. :)

I'm not confusing octane rating for potential energy. Nor am I confusing internal energy with the end result of how much power you net through more aggressive conditions. But the fact remains that 93 octane gasoline (100% gasoline or not) has less energy per unit volume than 87, and I don't have to look up that ethanol has less energy as well. As I said above, I already knew that. Us mechanical engineers know a thing or two about gasoline as well.

If you hold on a couple minutes, I'll find a you cookie for being a chemist. I think I'll have one myself.

93 octane gasoline (100% gasoline or not) has less energy per unit volume than 87

Depends on how the premium octane rating is attained (higher carbon chains in the mix, or additives). Gasolines are very complex mixtures, so generalizations are just that. To the best of my knowledge, both regular and premium gasolines have approximately 111,400 BTUs / gal. which makes them essentially equal. If the higher octane rating is obtained by additional ethanol blending, then I'll agree that the ethanol could dilute the energy rating downward. Higher compressions allow a more dense air/fuel mix, hence more power. Most regular fuel engines run about 9:1 CR. The G8GT is listed at 10.4:1 if Motor Trend knows what they're saying. That's getting closer to the 11:1 in my LS2 on the premium end, than 9:1 on the regular end. :dunno:

Since I don't have an owner's manual (yet), I don't know what Pontiac says in terms of fuel, or even if the "enhanced performance" statement is in the manual or not. The CR would "suggest" that regular might be a bit low unless they've done some aggresive ignition and valve timing detuning. But it all depends on the ability of the ECM to compensate for higher octane. If they've locked the ECM to regular specs and failed to allow it to compensate for higher octane, then regular is the best fuel for the car. I'm not sure we know that for sure.

Best answer would be a dyno comparison, since no one really knows. Have the engineers used regular as a base for emissions and EPA economy numbers and left us a gift in the use of premium? We won't solve that here. I'll try both when I have a chance unless someone else gets there first.

Good discussion that brings up more questions than it answers. Thanks for the cookie! Peace. :patriot:

The manual has been quoted as regular, unless pinging occurs for the V8. The same for the V6, while mentioning additionally that higher octane could be used for towing situations.

That statement seems to suggest that the V6 may be more adaptable to octane changes.

Ah, well. The dyno and strip will tell.

.... Since I don't have an owner's manual (yet), I don't know what Pontiac says in terms of fuel, or even if the "enhanced performance" statement is in the manual or not. ...


They may have picked up from PR material. Here is a link to the G8 press release.
http://media.gm.com/us/pontiac/en/product_services/r_cars/r_c_g8/080225_pr.htm

If you look to the specs at the bottom, it lists recommended fuel as regular and says "premium maximizes performance".

Chip

The manual has been quoted as regular, unless pinging occurs for the V8. The same for the V6, while mentioning additionally that higher octane could be used for towing situations.

That statement seems to suggest that the V6 may be more adaptable to octane changes.

I think it means that both engines are tuned much closer to the edge than "normal" GM products. The fact that towing is mentioned leads me to believe that high loads in certain situations could lead to pinging and loss of power. Therefore, premium in a towing situation will prevent loss of power due to pinging, but not increase the power.

Chip

The octane requirements for the V8 and V6 were described in seperate paragraphs. The V8 paragraph said nothing about premium, just the V6. What the premium did specifically for it... it didn't say.

Thank God, someone who understands! To recap (and answer your question) if the high octane table is tuned for 87-89 the ECM will NOT add timing over that so putting in 93 in a vehicle tuned for 87-89 has NO benefit other than less power and degraded fuel economy.

The inverse however is true if you put 87 in a vehicle tuned for 93 and beat on it, it'll knock itself right into the low octane table which is tuned for like 84 octane (IE water LOL)

Agree x2:patriot:

No reason to run anything higher than 87 on the L76 unless you feel like pouring just a little more $ into your tank.

"Premium maximizes performance." No one really knows what that means. Trailer towing is not much difference from high load performance driving or strip racing -- heavy engine loads. Is it not fair to assume that the so-called "high octane table" might not be limited to 87 octane? We don't know, do we?

For a daily driver, regular would seem to be appropriate. My concern is that 10.4:1 compression is quite high -- much higher than any car I'm familiar with running regular. The 5.7 hemi is 9-something:1 at 340HP and recommends mid-grade fuel. If GM warns of possible pre-ignition on regular, given the existence of 4-5 knock sensors on the block, then one could conclude that the use of regular fuel is very close to the lower limit of acceptability with everything adjusted to the max to prevent pre-ignition, and that the "high octane table" (someone else's terminology, not mine), which might adjust for the use of higher octane to "maximize performance" is actually set to utilize premium.

I'm not arguing here. I'm just very skeptical that they can build an engine at 10.4:1 to run acceptably on regular that isn't dialing back every parameter possible to accomplish that. And if that is so (might not be), then I would think the use of premium would "maximize performance". If you're not racing, then the real question is whether or not the long term use of regular in a high compression engine will cause eventual damage (well beyond the warranty period) as carbon build-up decreases combustion chamber size, raises compression and provides additional surface area to encourage additional pre-ignition.

I'd love to talk to a GM engineer about this. I just don't know how they're doing it. It's probably proprietary information, anyway .... no argument, just thinking out loud while waiting for mine to show up. :)

If GM warns of possible pre-ignition on regular, given the existence of 4-5 knock sensors on the block, then one could conclude that the use of regular fuel is very close to the lower limit of acceptability

I'm sure some don't... but every owners manual I've ever paid attention to has this statment, even GM's old Series I 3800 with 8.5:1 compression.

The EPA tests were conducted on premium fuel. My guess is that the engine is tuned for 91-93 but will run without knock (as the timing gets retarded from sensor input) on most 87. Full engine description at media.gm says it's designed to run on regular - yet teh press release for the sport truck recommends premium. This possibly has something to do with higher loading and towing. Octane does more than just produce power, it has an afect on combustion and exhaust temperature.

given the existence of 4-5 knock sensors on the block

You mean two? LOL Oh and just for you guys we are going to run a G8 GT on the dyno tomorrow with premium THEN tune it ;)

So let the guesses begin. I say 35hp gained by a premium retune.

So let the guesses begin. I say 35hp gained by a premium retune.

That would be inline with what we've seen from earlier cars (not production) This car will be a little broken in but not much so we'll see ;)

.... then one could conclude that the use of regular fuel is very close to the lower limit of acceptability with everything adjusted to the max to prevent pre-ignition, and that the "high octane table" (someone else's terminology, not mine), which might adjust for the use of higher octane to "maximize performance" is actually set to utilize premium...

The way I have always understood the typical high octane table would be more aggressive parameters (timing at least, and possibly other things) for when knock is not present. Low octane table is obviously set to prevent knock at all costs. You get enough knock and you jump to the low octane table. Which follows with everything that you have said.

On the G8, it was explained there is very little (maybe no) difference between the low and high octane tables. In other words, the "high octane" table is tuned (possibly very aggressively in comparison to typical GM tune) for 87 octane. So GM did leave some performance on the table. This is why Chris and company are able to gain 35 - 40 hp on a tune alone if you insert a 93 octane tune in the "high octane" table. I am probably oversimplifying, but I believe that is the gist of things.

Chip

Hi

I wanted to comment on this thread.

I do tuning for a living and have so for years now. We just got a 2008 G8 and like any good fellow would do we dove straight in to the computer.

The PCM in these G8's are tuned for premium IMHO. The very first pull on the stock file ran between 21-25 degrees of timing. This is by no means timing meant for 87 octane. HOWEVER the GM engine management strategy (since around 1993) has incorporated high and low octane modes. When repeated or consistent knock is present the computer takes a weighted average between a high and low octane tables braised on a learned octane scalar.

My opinion... These cars where designed for premium. HOWEVER they will run 87 with no problems other than sacrificed performance.

On the G8, it was explained there is very little (maybe no) difference between the low and high octane tables. In other words, the "high octane" table is tuned (possibly very aggressively in comparison to typical GM tune) for 87 octane. So GM did leave some performance on the table. This is why Chris and company are able to gain 35 - 40 hp on a tune alone if you insert a 93 octane tune in the "high octane" table. I am probably oversimplifying, but I believe that is the gist of things.

Chip

Sadly, this is not the case. The producting G8's run a fairly aggressive timing table and rely on the low octane table for running 87 octane.

Sadly, this is not the case. The producting G8's run a fairly aggressive timing table and rely on the low octane table for running 87 octane.

Alvin,

I welcome the additional info. I base my comments only on what had been discussed before. I obviously have no way to verify, since I do not have a G8 at hand. You bring new information to the table that could lead to one other possibility in my mind. Did GM do their SAE cert on 87 octane to purposely underate the power? Vector has already said they gained 35hp to the wheels with a 93 octane tune. I guess time will tell.

Chip

Hi,

I very much doubt 35rwhp is to be gained on a production vehicle without any dyno shannagans. I'll bet either one or two things is going on there.. Either GM rated them on 87 gas OR and this is a big OR... the camshaft is that weak on them. I know that GM has to sacrafice some to keep the DOD lifters happy and such. Maybe that is it? I know from experience the 5.3L DOD trucks are pathetic compared to the 5.3L non DOD trucks.


If anyone would care to see a hptuners pull out just email me and I'll forward it over to you. The stock file has borderline more timing than I would feel confortable to run in a vehicle like this.

I forsee gains in the 12-22rwhp realistic for the G8 in tuning. Anything more might be snake oil :oldfogey:

Hi,

I very much doubt 35rwhp is to be gained on a production vehicle without any dyno shannagans. I'll bet either one or two things is going on there.. Either GM rated them on 87 gas OR and this is a big OR... the camshaft is that weak on them. I know that GM has to sacrafice some to keep the DOD lifters happy and such. Maybe that is it? I know from experience the 5.3L DOD trucks are pathetic compared to the 5.3L non DOD trucks.


If anyone would care to see a hptuners pull out just email me and I'll forward it over to you. The stock file has borderline more timing than I would feel confortable to run in a vehicle like this.

I forsee gains in the 12-22rwhp realistic for the G8 in tuning. Anything more might be snake oil :oldfogey:

I'm not going to get into the HP gained because I don't have a dog in that hunt.

You have confirmed what alot of us have suspected that the timing is on the ragged edge (maybe a little over from what you are saying) of 87 and that the G8 may be a little happier on 93. I am pretty sure someone confirmed GM did the 361hp cert on 87 octane. If they didn't, someone please correct me. It is interesting because the EPA test was performed on premium.

Cam specs are elsewhere, something like 200/208 duration with .472/.479 lift. I don't think the cam is weak just because of DOD (supposedly safe to .590 lift), but is weak for gas mileage purposes.

Chip

The more I think of it the more I think its the cam. I've done 3-4 of the 5.3L DOD VVT trucks (which we don't have VVT) and stock they have been a baseline 220-235 and in comparison a 5.3L of a earlier year typically makes 245-270. Mind you that the older 5.3's have smaller throttle bodys. The only bad thing about that comparison is often trucks are configured so differently its hard to compare them apples to apples. For instance most of the 5.3L DOD trucks now adays are 3.42 geared even with 4x4 and the pretty big tires where i believe the older trucks where more often outfitted wtih 3.73's.

btw.. I think I've said this before but I'll say it again. If anyone wants the hptuner pullout for one of these let me know and I'll email it to you.

You mean two? LOL Oh and just for you guys we are going to run a G8 GT on the dyno tomorrow with premium THEN tune it ;)


Any results yet?

Any results yet?


I am pretty sure he is talking about Vector.

Any results yet?

Finishing up some other tests right now ;)

Cool. I saw that thread, but I didn't know he was in with them. :)

GM Powertrain says Premium.

GM Powertrain calls for Premium.

argue this all day long....my manual says 87 for the 8cyl and the same for the 6 UNLESS you are towing,then 89(for the 6cyl only)

And the EPA ratings are for 87-atleast thats what their website says

argue this all day long....my manual says 87 for the 8cyl and the same for the 6 UNLESS you are towing,then 89(for the 6cyl only)

And the EPA ratings are for 87-atleast thats what their website says

The EPA website for the G8 GT clearly says premium. That is one of the sources of confusion is what grade fuel was used for the different testing (SAE, EPA, etc.).

Chip

I just automatically used 93 because that is what I used in my GXP. I do wonder why a 35 hp bump with a tune seems unreal to some people. I know it is an L76 as opposed to an LS2, but if they were 400 hp, why can this not be? Especially because this was tuned for mileage and 87 octane. Wouldn't a tune for 93 octane easily give close to 400 hp?? Who is working on a tune? I held out on the GXP, but I want it on this! I think the other great help would be a tranny tune. It is pretty good in sport mode, but still feels confused sometimes. Can that be fixed with a TCM tune??

The EPA website for the G8 GT clearly says premium.
you are right,Chip.I read (either MT or edmunds or something) that epa tests were with regular.
I just emailed the epa website 2 questions. 1-what is the # for premium(91,92,93?)
2-why did they test with premium at all if the manual only recommends 87?

curious to see their reply

Im still waiting to hear someone do a dyno on 87 and record the HP and then someone to do a dyno on 93 and record the hp.

.
you are right,Chip.I read (either MT or edmunds or something) that epa tests were with regular.
I just emailed the epa website 2 questions. 1-what is the # for premium(91,92,93?)
2-why did they test with premium at all if the manual only recommends 87?

curious to see their reply

I believe (but im not sure) the universal octane level for premium is 91.

Over here its possible to buy 92 and 93...

In some states they sell 94 and 95...

And in other areas its nearly impossible to get anything over 91.

I just automatically used 93 because that is what I used in my GXP. I do wonder why a 35 hp bump with a tune seems unreal to some people. I know it is an L76 as opposed to an LS2, but if they were 400 hp, why can this not be? Especially because this was tuned for mileage and 87 octane. Wouldn't a tune for 93 octane easily give close to 400 hp?? Who is working on a tune? I held out on the GXP, but I want it on this! I think the other great help would be a tranny tune. It is pretty good in sport mode, but still feels confused sometimes. Can that be fixed with a TCM tune??

Since this vehicle is tuned for 87, you could easily get 30-35 HP from a tune, even without changing the intake or exhaust.

Downside is (if you think it is a downside) you would have to put 91-93 in it going forward. Depends on what is important to you.