YACT!!! Fuel...

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imported_goku

Diamond Member
Mar 28, 2004
7,613
3
0
Ok I'm currently in a "mini war" to which the enemies have never met but are angry at each other because of "hearsay".

Ok I've been talking to my friend about the reasons he uses High ocatane fuel over lower octane fuel and when I tried to explain this to my auto teacher, he laughed it off and disagreed. My friend says that:
1. Higher octane fuel causes less knocking (which I know to be true)

2. Using the higher octane fuel will cause less carbon deposits than regular.

Auto teacher says that high octane and low octane fuel cause the same amount of carbon desposits because they both have good amounts of detergent in them now. The reason for carbon desposits is because either the fuel injectors are worn out and I guess outputting too much fuel or not making a spray (likely both). Or the computer is not controlling the fuel properly and therefore outputting too much fuel (like the first point). Having too much fuel left over after the burn is causing the carbon deposits.

So, who is correct?
 
deadlyapp

deadlyapp

Diamond Member
Apr 25, 2004
6,672
744
126
auto teacher sounds right to me. Running rich causes the excess carbon deposits, so unburnt fuel, and extra fuel will cause it. I dont think it matters so much what octane rating the fuel is.
 
Ryan

Ryan

Lifer
Oct 31, 2000
27,519
2
81
Originally posted by: Gravity
Higher octane fuel makes a difference.
Click to expand...

Only if your car can take advantage of it. It you're putting high octane in your Civic or other economy car, you're a tool.
 
H

Heisenberg

Lifer
Dec 21, 2001
10,621
1
0
Originally posted by: Ryan
Originally posted by: Gravity
Higher octane fuel makes a difference.
Click to expand...

Only if your car can take advantage of it. It you're putting high octane in your Civic or other economy car, you're a tool.
Click to expand...
Indeed. You should only use higher octane if your car specifically needs it.
 
I

Ilmater

Diamond Member
Jun 13, 2002
7,516
1
0
Originally posted by: Gravity
Higher octane fuel makes a difference... if your car has a compression ratio of 9:1 or greater ONLY.
Click to expand...
I know everyone gives heresay stories, but I can tell you 100% this is true. A man that used to work at an oil company taught a class that he and a bunch of other mechanics were attending (my cousin had recently quit being a mechanic to teach at the local VoTech school). This teacher asked everyone in the room to raise their hands if they used premium gasoline ever in their cars (super and ultimate grades; anything above regular). A few of them raised their hands, and he said, "You're wasting your money." He proceeded to tell them that while he worked at the oil company, he saw TONS of reports that were basically inconclusive on whether or not it was worth using higher-octane fuel.

The one caveat to this was on higher-compression (usually turbo) engines, and he said that the manufacturer will put their recommended octane rating in their manuals, so just follow what they said.
 
iamwiz82

iamwiz82

Lifer
Jan 10, 2001
30,772
13
81
Originally posted by: Ilmater
Originally posted by: Gravity
Higher octane fuel makes a difference... if your car has a compression ratio of 9:1 or greater ONLY.
Click to expand...
I know everyone gives heresay stories, but I can tell you 100% this is true. A man that used to work at an oil company taught a class that he and a bunch of other mechanics were attending (my cousin had recently quit being a mechanic to teach at the local VoTech school). This teacher asked everyone in the room to raise their hands if they used premium gasoline ever in their cars (super and ultimate grades; anything above regular). A few of them raised their hands, and he said, "You're wasting your money." He proceeded to tell them that while he worked at the oil company, he saw TONS of reports that were basically inconclusive on whether or not it was worth using higher-octane fuel.

The one caveat to this was on higher-compression (usually turbo) engines, and he said that the manufacturer will put their recommended octane rating in their manuals, so just follow what they said.
Click to expand...

So he asked that before finding out who is running a high compression engine? Seems like a bad teacher to me.

A buddy of mine had a an old 258 I6 in his CJ7 that would ping on anything less than 91 octane.
 
I

imported_goku

Diamond Member
Mar 28, 2004
7,613
3
0
Originally posted by: Ilmater
Originally posted by: Gravity
Higher octane fuel makes a difference... if your car has a compression ratio of 9:1 or greater ONLY.
Click to expand...
I know everyone gives heresay stories, but I can tell you 100% this is true. A man that used to work at an oil company taught a class that he and a bunch of other mechanics were attending (my cousin had recently quit being a mechanic to teach at the local VoTech school). This teacher asked everyone in the room to raise their hands if they used premium gasoline ever in their cars (super and ultimate grades; anything above regular). A few of them raised their hands, and he said, "You're wasting your money." He proceeded to tell them that while he worked at the oil company, he saw TONS of reports that were basically inconclusive on whether or not it was worth using higher-octane fuel.

The one caveat to this was on higher-compression (usually turbo) engines, and he said that the manufacturer will put their recommended octane rating in their manuals, so just follow what they said.
Click to expand...

Did he assume everybody in the class drove a honda civic or accord?
 
T

theMan

Diamond Member
Mar 17, 2005
4,386
0
0
almost all cars today take any octane. so, why pay more for high octane, when you dont have to? unless you need a few more horsepower to compensate for something small...
 
iamwiz82

iamwiz82

Lifer
Jan 10, 2001
30,772
13
81
Originally posted by: theman
almost all cars today take any octane. so, why pay more for high octane, when you dont have to? unless you need a few more horsepower to compensate for something small...
Click to expand...

And posting your computer in your signature isn't compensating? Hmmm...
 
Ryan

Ryan

Lifer
Oct 31, 2000
27,519
2
81
Originally posted by: theman
almost all cars today take any octane. so, why pay more for high octane, when you dont have to? unless you need a few more horsepower to compensate for something small...
Click to expand...

Do you have a small brain?
 
Q

Quixfire

Diamond Member
Jul 31, 2001
6,892
0
0
Auto Teacher is correct and running an engine on High Octane fuel that does require it will leave more unburned fuel to develop carbon deposits.

Octane is the ability for fuel to ignite under compression, the higher the compression the higher the need octane. High-octane fuel in a low compression engine can ignite to quickly leaving more unburned fuel in the exhaust to form deposits.
 
C

cavemanmoron

Lifer
Mar 13, 2001
13,664
28
91
Originally posted by: iamwiz82
Originally posted by: Ilmater
Originally posted by: Gravity
Higher octane fuel makes a difference... if your car has a compression ratio of 9:1 or greater ONLY.
Click to expand...
I know everyone gives heresay stories, but I can tell you 100% this is true. A man that used to work at an oil company taught a class that he and a bunch of other mechanics were attending (my cousin had recently quit being a mechanic to teach at the local VoTech school). This teacher asked everyone in the room to raise their hands if they used premium gasoline ever in their cars (super and ultimate grades; anything above regular). A few of them raised their hands, and he said, "You're wasting your money." He proceeded to tell them that while he worked at the oil company, he saw TONS of reports that were basically inconclusive on whether or not it was worth using higher-octane fuel.

The one caveat to this was on higher-compression (usually turbo) engines, and he said that the manufacturer will put their recommended octane rating in their manuals, so just follow what they said.
Click to expand...

So he asked that before finding out who is running a high compression engine? Seems like a bad teacher to me.

A buddy of mine had a an old 258 I6 in his CJ7 that would ping on anything less than 91 octane.
Click to expand...


Octane requirment is NOT based only on compression,
combustion chamber design also,
ignition timing,
carb/efi lean/richness.

I burnt some pistons in an engine once,I had milled the heads,and made the squish
band so small the engine was in need of either 110 octane,
or it would detonate so bad,that it would ruin the pistons.

I ruined 2 sets of pistons,before I figured out,what I did wrong.

Had to take the heads back to the machine shop,and have the combustion chambers
opened back up to increase the squish band.

The total compression ratio was safe for 92 octane,but the outer edge
of the squish band was what caused the problems.

I also years ago had leaned down a carb on my Chevy Van,And at the same time cranked the timing way up;
it would "ping" unless I put 92+ octane in it,and when cold outside it would ping,
even with the 92-93 octane gas.

In the spring I pulled the plugs out,most of them the electrodes were almost gone,
I had to rejet,back to where it was before.
 
C

cjgallen

Diamond Member
Jan 20, 2003
6,419
0
0
Originally posted by: Heisenberg
Originally posted by: Ryan
Originally posted by: Gravity
Higher octane fuel makes a difference.
Click to expand...

Only if your car can take advantage of it. It you're putting high octane in your Civic or other economy car, you're a tool.
Click to expand...
Indeed. You should only use higher octane if your car specifically needs it.
Click to expand...

Even the old motor in my beetle with horrible compression didn't knock with the cheap stuff :)
 
C

Czervik

Member
Aug 29, 2003
32
0
66
Octane is actually a detonation "preventative". Higher octane is needed in high compression engines to prevent premature detonation, as regular fuel can ignite/explode before the spark plug fires. Putting high octane in a car that takes regular 87 is plain wasteful and can cause a dirty engine. Putting regular in a high compression engine (rec 91 or higher), is BAD for your engine.
 
V

Viperoni

Lifer
Jan 4, 2000
11,084
1
71
Higher octane fuel run in an engine which doesn't require or benefit from it... longer fuel burn times, possibly higher unburned fuel entering exhaust system... more carbon buildup?
 
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