regular vs. premium gasoline?

[Don Vito Corleone]

Originally posted by: RobCur
funny, how no one seem to know why their are 3 grades? yet you ali,say its different octane level well duh! which is 3 different quality(same thing, worded differently!). all car manual says unleaded fuel, not plus or premium. Its a matter of choice and preferences..
Why use lowest octane on a weak car??? it does not make sense to pay less for a very fuel efficent car like volkswagon etc or any small engine.
this arguement is getting pointless.es.s.s buy whatever you want and say whatever you like.. end of discusssiosns.s

I think this must be a joke, but it's so much more entertaining to think it isn't . . .

 

[Slickone]

Originally posted by: FritzoAnyway, I was always told to use 87 unless A) you're getting spark knock, or B) You have a turbo or a supercharger.

And having a (factory installed) turbo or supercharger doesn't necessarly mean you need a high octane. They do use a lower compression ratio on forced induction cars. My 300ZX turbo calls for 87.

Originally posted by: JediJeb
I have a 99 Trans Am and if I use regular gas it will ping and gets about 5-7 mpg less than on premium. The premium is slower burning and harder to ignite which eliminates the ping or knocking. If the engine pings it will retard the spark advance to compensate and that reduces the effeciency of the engine and causes a big loss of power also. Low compression ratio engines get by with less octaine rating.

Yep I think that's been stated a few times.

On older non computer controlled engines with high compression ratios in a pinch you can actually get by with using regular and adding a couple pints of diesel fuel to the mix to raise the octaine rating, it smokes like crazy but it works .

Wouldn't diesel lower the octane rating? Diesel does have a very low resistance to knock.

 

[Pacfanweb]

Originally posted by: Slickone
On older non computer controlled engines with high compression ratios in a pinch you can actually get by with using regular and adding a couple pints of diesel fuel to the mix to raise the octaine rating, it smokes like crazy but it works .

Wouldn't diesel lower the octane rating? Diesel does have a very low resistance to knock.[/quote]
No, diesel is MUCH harder to ignite than gas. Diesel does not have a low resistance to knock, considering that most diesels run around 22:1 compression.
Adding diesel to gas would basically raise the octane......just smell most any octane booster, and you'll definitely think it smells like diesel or kerosene.

 

[Eli]

Originally posted by: Pacfanweb

Originally posted by: Slickone
On older non computer controlled engines with high compression ratios in a pinch you can actually get by with using regular and adding a couple pints of diesel fuel to the mix to raise the octaine rating, it smokes like crazy but it works .

Wouldn't diesel lower the octane rating? Diesel does have a very low resistance to knock.

No, diesel is MUCH harder to ignite than gas. Diesel does not have a low resistance to knock, considering that most diesels run around 22:1 compression.
Adding diesel to gas would basically raise the octane......just smell most any octane booster, and you'll definitely think it smells like diesel or kerosene.[/quote]Incorrect.

A diesel engine works differently than a gasoline engine. It does not draw the already mixed fuel/air into the engine. It only draws air into the combustion chamber via the intake stroke.

The air is then compressed to the aforementioned ~22:1 compression ratio.

When the diesel fuel is injected, it immediately combusts in the superheated, compressed air.

Diesel is rated by its cetane number, which is the exact opposite of Octane. It measures how easy the fuel is to spontaneously ignite. The higher the number, the easier. You can actually buy additives for diesel to raise the cetane number, the same way you can buy additives that raise the octane number for gasoline.

So, he is right. Not only would that seriously mess with your fuel system, it does not raise the octane.

 

[Pacfanweb]

Okay, then why does octane booster smell exactly like diesel fuel?

 

[Eli]

Originally posted by: Pacfanweb
Okay, then why does octane booster smell exactly like diesel fuel?

I dunno..

Can your nose distinguish every hydrocarbon chain from C2H4 to C12H24 and beyond?

Many of them smell quite similar, especially when mixed together. I'm sure cetane boosters smell the same, even though they lower the octane.

 

[Slickone]

Originally posted by: Pacfanweb

Originally posted by: Slickone
On older non computer controlled engines with high compression ratios in a pinch you can actually get by with using regular and adding a couple pints of diesel fuel to the mix to raise the octaine rating, it smokes like crazy but it works .

Wouldn't diesel lower the octane rating? Diesel does have a very low resistance to knock.

No, diesel is MUCH harder to ignite than gas. Diesel does not have a low resistance to knock, considering that most diesels run around 22:1 compression.
Adding diesel to gas would basically raise the octane......just smell most any octane booster, and you'll definitely think it smells like diesel or kerosene.[/quote]

Link (yeah this is a forum post, but from a Laboratory of Atmospheric Chemistry Grad student):
Diesel has low volatility, low knock resistance, yet high energy per volume. Because of its low knock resistance, diesel should not be used in a gasoline engine as it will destroy it very quickly and efficiently.


Link:
General rules:
Heavy fuels (diesel, jet): Low volatility, low knock resistance, and high energy per volume
Light fuels (gasoline): High volatility, high knock resistance, and low energy per volume

Note that gasoline, partially, makes up for its (relatively) low energy-per gallon by the fact that a gallon of gasoline weighs less (by about 15%) than a gallon of jet fuel. Octane rating is in no way correlated with engine power or efficiency. There is more potential energy in a gallon of diesel fuel than a gallon of gasoline, yet the diesel fuel has a much lower octane value (more on that below).
[cut]
Diesel and Jet fuel (along with kerosene) have, indeed, terrible octane numbers; typically about 15-25 "octane". They tend to ignite easily from high compression. Their use in a gasoline engine will quickly destroy it.

I don't know how many times I've heard people say they're friend/dad/uncle runs/ran jet fuel in their hot rod, to which I ask if they know it's a lower octane and would screw up the engine (they usually mean race fuel) . I learned this as a kid (dad's a pilot) and in my propulsion class way back in college (I'm a pilot).