Regular or premium????
Intermediate
Joined: Sep 2017
Posts: 27
Likes: 9
From: Dataw Island SC
That was the question that made me look it up. Octane ratings close to 100 or above 100 are achieved by adding MTBE or tetra-ethyl lead. Good article here:
https://science.howstuffworks.com/gasoline.htm
https://science.howstuffworks.com/gasoline.htm
Race Director
Joined: Oct 2008
Posts: 17,982
Likes: 1,074
From: Lansing MI
Yeah it basically says the chemical equivalent of octane/heptane, so its not actually octane and heptane plus trace chemistry. Instead, that's just how its measured or rated. So 110 octane fuel would have the combustion properties as 100 percent octane, that's concentrated by 10%, and no heptane. Simple.
Last edited by PatternDayTrader; Oct 29, 2017 at 08:30 AM.
Melting Slicks
Joined: Jul 2005
Posts: 2,649
Likes: 863
The fact is that there are a lot of different things going on with car engines. I have known people at work who had cars that were apparently so carboned up - that engines that were rated to run on regular needed premium to avoid significant knocking - one of these was a Ford V-8 and another was in a Subaru 4 Cyl. You would think the knock sensors would tell the EFI Computer to intervene - but apparently not - no check engine light on - so presumption is that the knock sensor was OK ...
Tom400FI - the engine I was referring to was a late 1990's Ferrari with a very high compression ratio. One of the people I spent time with at the track related a story where the engine in an acquaintances car was badly damaged (supposedly several cracked pistons, & Yes, it was supposedly being run at the track) and Ferrari would not cover the damage under warranty saying the car was run on too low an octane.
Tom400FI - the engine I was referring to was a late 1990's Ferrari with a very high compression ratio. One of the people I spent time with at the track related a story where the engine in an acquaintances car was badly damaged (supposedly several cracked pistons, & Yes, it was supposedly being run at the track) and Ferrari would not cover the damage under warranty saying the car was run on too low an octane.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Tom400FI - the engine I was referring to was a late 1990's Ferrari with a very high compression ratio. One of the people I spent time with at the track related a story where the engine in an acquaintances car was badly damaged (supposedly several cracked pistons, & Yes, it was supposedly being run at the track) and Ferrari would not cover the damage under warranty saying the car was run on too low an octane.
Instructor
Joined: May 2017
Posts: 176
Likes: 3
From: VA
i have a 1991 l98
i did a complete tune up in the last year and advanced the timing to 7
stock advance is 6
my car knocks like mad at first start up if i run mid grade
i have found that i have to run premium.
the car is 26 years old too. so...got that going for me.
i did a complete tune up in the last year and advanced the timing to 7
stock advance is 6
my car knocks like mad at first start up if i run mid grade
i have found that i have to run premium.
the car is 26 years old too. so...got that going for me.
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Team Owner
Joined: Sep 2001
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From: Athens AL
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Use what octane the engine requires, nothing higher. Higher octane does not equal better gas.
Best thing anyone can do is get familiar with a scanner/laptop, and check knock counts. If you see it knocking and the ECM pulls timing back, then you need to go up to the next grade of octane in your area. Otherwise you are just guessing. Relying on your hearing to detect knock only seems to work when the knock is particularly bad. Injector tick and rattling in a C4 is just too prominent to recommend relying on any of that for someone who doesn't know.
Best thing anyone can do is get familiar with a scanner/laptop, and check knock counts. If you see it knocking and the ECM pulls timing back, then you need to go up to the next grade of octane in your area. Otherwise you are just guessing. Relying on your hearing to detect knock only seems to work when the knock is particularly bad. Injector tick and rattling in a C4 is just too prominent to recommend relying on any of that for someone who doesn't know.
Last edited by vader86; Oct 30, 2017 at 12:01 PM.
Melting Slicks
Joined: May 2013
Posts: 2,692
Likes: 349
From: Sacramento California
Every car has an owner's manual that will explain the fuel requirements.
Here are the basics for gasoline engines:
-- High-performance cars with forced induction or high-compression engines often *require* premium. Usually the gas fill door will say "premium fuel required" in huge bold letters, and these words will be displayed near the fuel gauge as well.
-- Some cars are "premium recommended" such as my 1995 LT-1 Corvette. The owner's manual says "use 91 octane or higher for best performance." The manual also says the engine will run OK on gasoline below 91 octane, although at reduced power levels, but do not run gasoline below 87 octane.
-- All other cars run fine on regular gasoline.
-- Direct-injected engines (GDI) warrant a separate discussion thread.
-- my gas mower will run on Bacardi 151
Here are the basics for gasoline engines:
-- High-performance cars with forced induction or high-compression engines often *require* premium. Usually the gas fill door will say "premium fuel required" in huge bold letters, and these words will be displayed near the fuel gauge as well.
-- Some cars are "premium recommended" such as my 1995 LT-1 Corvette. The owner's manual says "use 91 octane or higher for best performance." The manual also says the engine will run OK on gasoline below 91 octane, although at reduced power levels, but do not run gasoline below 87 octane.
-- All other cars run fine on regular gasoline.
-- Direct-injected engines (GDI) warrant a separate discussion thread.
-- my gas mower will run on Bacardi 151
Melting Slicks
Joined: May 2013
Posts: 2,692
Likes: 349
From: Sacramento California
There are a few products that will increase octane several full points, and they tend to be expensive "race fuel" type additives. Here is one that cost $29 per quart: https://www.maperformance.com/produc...el-concentrate
Obviously it's best to buy your octane at the pump when you can.
Drifting
Joined: Feb 2016
Posts: 1,384
Likes: 339
From: Simi Valley CA
Yes, there is a lot more in gas than heptane and octane. The octane rating is based on the simple formula. Now there's Ethanol and a bunch of other additives. The 110+ octane race fuels use the mathematical formula for the rating. I had a super gas drag car with 13.75 CR and it used 116 race fuel. That stuff has a sweet smell to it, nothing like gasoline.
Melting Slicks
Joined: May 2013
Posts: 2,692
Likes: 349
From: Sacramento California
I have wondered how much additional timing (and power) would be available by adding a few gallons of 100 octane from the local Flyers gas station. I don't mean a fill-up, not at $8 per gallon, but a few gallons to raise the octane in my tank from 91 to about 93 or 94.
Anyone done this, and able to compare how the LT1 or LT4 performs differently between the two (91 octane and 93/94)?
Thanks
Anyone done this, and able to compare how the LT1 or LT4 performs differently between the two (91 octane and 93/94)?
Thanks
Pro
Joined: Sep 2012
Posts: 508
Likes: 89
From: Bowie MD
I have wondered how much additional timing (and power) would be available by adding a few gallons of 100 octane from the local Flyers gas station. I don't mean a fill-up, not at $8 per gallon, but a few gallons to raise the octane in my tank from 91 to about 93 or 94.
Anyone done this, and able to compare how the LT1 or LT4 performs differently between the two (91 octane and 93/94)?
Thanks
Anyone done this, and able to compare how the LT1 or LT4 performs differently between the two (91 octane and 93/94)?
Thanks
Best
Jerry
Last edited by gdgeorge; Nov 2, 2017 at 10:53 AM.
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From: Compound in the Grove, Ga.
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I always use 91+ but than I also have 11 to 1 compression. 
Melting Slicks
Joined: May 2013
Posts: 2,692
Likes: 349
From: Sacramento California
I don't have anything empirical on paper, and the car is faster than I drive. Having said that, anecdotally: I see no difference between the mid-grade and high-test except, perhaps, a minimal MPG improvement. Mixing the two doesn't seem to have any effect, and I wouldn't expect it to. I discovered that the car runs poorly on regular when SWMBO filled up with the stuff. The car demonstrated hard starting, hesitation, and run-on... As soon as I got the thing to half a tank, I added high-test and that resolved the issues immediately.
Best
Jerry
Best
Jerry
I was wondering specifically about performance boost (if any) when going from 91 octane to 93 octane... not dyno numbers, just general SOTP impressions of "better performance"
Pro
Joined: Sep 2012
Posts: 508
Likes: 89
From: Bowie MD
Understood. In that case, no. I have not noticed a performance difference between the mid-grade and high test gasolines in the BaltoWash area.
Best,
Jerry
Last edited by gdgeorge; Nov 2, 2017 at 11:24 AM.