GXP fuel mileage ??
TECH Fanatic
Joined: Jul 2007
Posts: 1,115
Likes: 0
From: Reading, Pennsylvania
People need to understand the difference between an engine requiring a certain octane of gas and it recommending a certain octane. The LS4 does not REQUIRE 91+ it merely states it is recommended but will run on regular. You just may experience "decreased performance." Unless you're tuned for premium the LS4 is fine with 87. I ran mine on 89 for the first few months I had it and then later switched to 92/93 til I got rid of it. Have a buddy who got an 06 SS and has ran it on 87 since brand new.
TECH Fanatic
Joined: Jul 2007
Posts: 1,115
Likes: 0
From: Reading, Pennsylvania
Which would fall into the "decreased performance" issue. I personally never noticed a difference between mine with premium and my buddies on 87. Then again our cars were both stock. Also got around the same gas mileage, he may have even got slightly better. Regardless it was only a couple bucks more to put in 92/93 so I did, but it won't cause any harm running on 87.
As you can see in my sig, I'm a Master Tech at a Chevy dealership. I've never seen a single document published stating that the LS4 in the Impala SS or any other model is recommended for premium fuel. Typically when they suggest higher octane fuel, it says so on the inside of the gas door or on the dash (in the old days).
I tried running 93 in my car for two weeks and the mileage got worse and there was no performance increase. The LS4s have a problem with high IATs due to the bad MAF location and exhaust crossover. High IATs retard timing. 93 octane is suggested for vehicles with high compression/advanced timing. Unless you lower your IATs, 93 in your STOCK LS4 wont do anything for you.
I would like to see some documentation to back up this rumor. Thanks!
I tried running 93 in my car for two weeks and the mileage got worse and there was no performance increase. The LS4s have a problem with high IATs due to the bad MAF location and exhaust crossover. High IATs retard timing. 93 octane is suggested for vehicles with high compression/advanced timing. Unless you lower your IATs, 93 in your STOCK LS4 wont do anything for you.
I would like to see some documentation to back up this rumor. Thanks!
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Verdad Gallardo TECH Fanatic
Joined: Jul 2007
Posts: 1,115
Likes: 0
From: Reading, Pennsylvania
As you can see in my sig, I'm a Master Tech at a Chevy dealership. I've never seen a single document published stating that the LS4 in the Impala SS or any other model is recommended for premium fuel. Typically when they suggest higher octane fuel, it says so on the inside of the gas door or on the dash (in the old days).
I tried running 93 in my car for two weeks and the mileage got worse and there was no performance increase. The LS4s have a problem with high IATs due to the bad MAF location and exhaust crossover. High IATs retard timing. 93 octane is suggested for vehicles with high compression/advanced timing. Unless you lower your IATs, 93 in your STOCK LS4 wont do anything for you.
I would like to see some documentation to back up this rumor. Thanks!
I tried running 93 in my car for two weeks and the mileage got worse and there was no performance increase. The LS4s have a problem with high IATs due to the bad MAF location and exhaust crossover. High IATs retard timing. 93 octane is suggested for vehicles with high compression/advanced timing. Unless you lower your IATs, 93 in your STOCK LS4 wont do anything for you.
I would like to see some documentation to back up this rumor. Thanks!
11 Second Club
Joined: Nov 2005
Posts: 606
Likes: 1
From: NY
As you can see in my sig, I'm a Master Tech at a Chevy dealership. I've never seen a single document published stating that the LS4 in the Impala SS or any other model is recommended for premium fuel. Typically when they suggest higher octane fuel, it says so on the inside of the gas door or on the dash (in the old days).
I tried running 93 in my car for two weeks and the mileage got worse and there was no performance increase. The LS4s have a problem with high IATs due to the bad MAF location and exhaust crossover. High IATs retard timing. 93 octane is suggested for vehicles with high compression/advanced timing. Unless you lower your IATs, 93 in your STOCK LS4 wont do anything for you.
I would like to see some documentation to back up this rumor. Thanks!
I tried running 93 in my car for two weeks and the mileage got worse and there was no performance increase. The LS4s have a problem with high IATs due to the bad MAF location and exhaust crossover. High IATs retard timing. 93 octane is suggested for vehicles with high compression/advanced timing. Unless you lower your IATs, 93 in your STOCK LS4 wont do anything for you.
I would like to see some documentation to back up this rumor. Thanks!
Actually I'm a World Class Tech which is above a master tech, but that is besides the point.
I'll admit I am wrong this time. I don't have an owners manual for my car because I bought it used. It took searching in the Service Information Owners Manual section to come up with a black & white answer. Document #1570979 reads:
**** son, looks like I've been running the wrong gas for 11k miles. Nobody at my dealer even knows that these motors are supposed to run premium fuel, nor does it say it anywhere on my car. I stand corrected.
I'll admit I am wrong this time. I don't have an owners manual for my car because I bought it used. It took searching in the Service Information Owners Manual section to come up with a black & white answer. Document #1570979 reads:
If your vehicle has the 3800 Supercharged V6 engine (VIN Code 4) or the 5.3L V8 engine (VIN Code C), use premium unleaded gasoline with a posted octane rating of 91 or higher. You may also use regular unleaded gasoline rated at 87 octane or higher, but your vehicle's acceleration may be slightly reduced, and you may notice a slight audible knocking noise, commonly referred to as spark knock. If the octane is less than 87, you may notice a heavy knocking noise when you drive. If this occurs, use a gasoline rated at 87 octane or higher as soon as possible. Otherwise, you might damage your engine. If you are using gasoline rated at 87 octane or higher and you hear heavy knocking, your engine needs service.
TECH Enthusiast
Joined: Apr 2007
Posts: 697
Likes: 0
From: Hudson River Valley, NY
I ran regular in my car for a little while and it surged while lugging it. I'm sure it was knocking up a storm, never again will I run regular. The compression on these engines is 10:1 as posted which right there says it for itself one should run high test.
Why does the truck engine which makes similar power run happily on regular fuel??? WTF! They couldn't make the LS4 same way?
Why does the truck engine which makes similar power run happily on regular fuel??? WTF! They couldn't make the LS4 same way?
Its been 15-35 degrees here lately and my average stop-n-go commute has been getting me about 15.2-15.4 mpg avg on the DIC using Shell 93. Since 93 isn't as volatile as 87, I figured there was better mileage to be had. Since I'm not driving my car hard anyways cuz of the snow, I put 5 gallons of 87 in on the last fill up and then used 93 for the rest of the tank. In theory this gives me a mix of about 91 octane or so. My avg mpg has now been at 16.8 mpg for the past three days. Food for thought...
TECH Fanatic
Joined: Jan 2007
Posts: 1,029
Likes: 0
From: LITH, IL.
Compression alone does not require Octane higher than 87 to run properly. It is the overall design of the combustion chamber and timing. Quench area, flow dynamics, etc. all play a roll. For example, my dearly departed XJS also ran a 5.3L aluminum block/heads with 11.5:1 compression. The manual called for 87 Octane fuel and it ran happily on it all day long, no knock retard, no decreased performance. The following model year, they changed the ignition system and slightly altered the timing (engine was the same) and it then required the 91+ Octane fuel. A rather specific example of course, but looking at a single variable in an engine seldom gives a true picture of what is going on.
A few things....Shell gas is garabage, i have dyno pulls to prove it.
My father works in a Sonoco refinery and they test the differences between grades of gases. The higher octane CAN improve performance if your car is TUNED for it. BUT you WILL get better gas milage on 87. This is because the 93 burns so quickly that it isnt possible for your car to burn all of it before it exits your cylinders. 87 makes better use of all your gas. under most circumstances that is.
And since i did my cam, got rid of DOD and did my intake, i average about 19mpg on the highway and have to fill up everyday. I used to get 35-40mpg on the highway and fill up once a week.
My father works in a Sonoco refinery and they test the differences between grades of gases. The higher octane CAN improve performance if your car is TUNED for it. BUT you WILL get better gas milage on 87. This is because the 93 burns so quickly that it isnt possible for your car to burn all of it before it exits your cylinders. 87 makes better use of all your gas. under most circumstances that is.
And since i did my cam, got rid of DOD and did my intake, i average about 19mpg on the highway and have to fill up everyday. I used to get 35-40mpg on the highway and fill up once a week.
TECH Regular
Joined: Nov 2009
Posts: 446
Likes: 0
From: Farmington Hills, MI
87 Octane fuel has more energy per gallon than 91+. But, with an engine built and tuned for 91+ you make more power with 91+ than with 87 and your fuel economy is usually better with 91+. It depends on a lot though. The big reason is the higher your compression the more effecient combustion is. Also, dynamic compression is more important to octane sensitivity than static compression. If you run a big enough cam with a late closing intake valve you can run a much higher static compression on pump gas. Just to show an extreme example, diesel engines get great mileage because diesel fuel has about 30% more energy per gallon than gasoline and because the compression is high, although ideal compression is around 15:1-16:1. The open throttle helps too, and efficiency doesn't fall off as much during light loads because of it.
Dude, Chicago gas is garbage. I'm sure you don't have to run oxygenated or reformulated fuel. Does your fuel have 10% ethanol added to it? I wish I had a Sunoco here. At least you can choose 91 octane, I only have 87, 89, and 93. I never use 89 octane because nobody ever buys it so I assume that the stuff in the tank is old. In fact, the only gas station in our arear that even made GM's Top-Tier list was Shell (see: http://www.toptiergas.com/retailers.html). So how can you call it garbage when GM says its the best? Here's the big name gas stations in my area, you tell me what you would choose:
Shell
BP (Amaco)
Mobil
Speedway
Citgo
Marathon
7 Eleven
I only am playing around with mixing in 87 octane because of the below freezing temps and the volatility of 87 vs 93 in the weather. I think the volatility of 93 is too low to run in these temperatures. Plus I'm not worried about detonation or spark knock because there is snow on the ground, where am i gonna go?
In the summertime I'll run straight 93 and enjoy my power then.
Shell
BP (Amaco)
Mobil
Speedway
Citgo
Marathon
7 Eleven
I only am playing around with mixing in 87 octane because of the below freezing temps and the volatility of 87 vs 93 in the weather. I think the volatility of 93 is too low to run in these temperatures. Plus I'm not worried about detonation or spark knock because there is snow on the ground, where am i gonna go?
In the summertime I'll run straight 93 and enjoy my power then. 
On The Tree
Joined: Nov 2009
Posts: 129
Likes: 0
From: St. Louis, MO
A few things....Shell gas is garabage, i have dyno pulls to prove it.
My father works in a Sonoco refinery and they test the differences between grades of gases. The higher octane CAN improve performance if your car is TUNED for it. BUT you WILL get better gas milage on 87. This is because the 93 burns so quickly that it isnt possible for your car to burn all of it before it exits your cylinders. 87 makes better use of all your gas. under most circumstances that is.
And since i did my cam, got rid of DOD and did my intake, i average about 19mpg on the highway and have to fill up everyday. I used to get 35-40mpg on the highway and fill up once a week.
My father works in a Sonoco refinery and they test the differences between grades of gases. The higher octane CAN improve performance if your car is TUNED for it. BUT you WILL get better gas milage on 87. This is because the 93 burns so quickly that it isnt possible for your car to burn all of it before it exits your cylinders. 87 makes better use of all your gas. under most circumstances that is.
And since i did my cam, got rid of DOD and did my intake, i average about 19mpg on the highway and have to fill up everyday. I used to get 35-40mpg on the highway and fill up once a week.
