Octane ratings

  • Thread starter Thread starter billyboy24d
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billyboy24d

Just to get it straight......higher octane ratings DOES NOT mean
slower burn time, it means that the gas can withstand higher heat and
pressure before an uncontroled explosion. The only to use high octane
is to help prevent pinging and detonation in high compression and
forced induction engines. Racing fuel is always above 100 octane, and
some is as high as 140. This would not work at 8000 rpm if it was a
slow burn time. For the problem with the Elantra, check the cat. it
may be cloging. If it is, the back pressure would cause more heat and
detonation. The problem would be amplified a high rpm or under a heavy
load, like going up a hill. Higher octane may help a little, but I
don't think it will solve the problem. Get it checked out soon.
Detonation and pinging will ruin your engine.
Bill
 
billyboy24d said:
Just to get it straight......higher octane ratings DOES NOT mean
slower burn time, it means that the gas can withstand higher heat and
pressure before an uncontroled explosion. The only to use high octane
is to help prevent pinging and detonation in high compression and
forced induction engines. Racing fuel is always above 100 octane, and
some is as high as 140. This would not work at 8000 rpm if it was a
slow burn time.
Click to expand...

Sorry Bill, but that's incorrect. Racing fuels only work efficiently in
very high compression engines, or those that are highly boosted through
turbocharging or supercharging. The extreme heat and pressure created by
the high compression and/or boost cause the high octane fuel to burn
faster than it would in a lower compression engine. The burn rate of a
given fuel is a function of heat and pressure, it's not constant.
For the problem with the Elantra, check the cat. it
may be cloging. If it is, the back pressure would cause more heat and
detonation.
Click to expand...

A clogged cat generally just causes a loss of power. I've never heard of
one causing detonation and if you think about it, it seems pretty
unlikely. High backpressure prevents exhaust gasses from exiting the
cylinders efficiently. Exhaust gas that isn't expelled has the effect of
reducing combustion temperatures, which is why engines used EGR
(Exhaust Gas Recirculation) systems to reduce combustion temps (which
reduces the formation of certain pollutants).
The problem would be amplified a high rpm or under a heavy
load, like going up a hill.
Click to expand...

That's typical of knocking/pinging problems in general.
Higher octane may help a little, but I
don't think it will solve the problem. Get it checked out soon.
Detonation and pinging will ruin your engine.
Click to expand...

Definitely.
 
"Racing fuel is always ...." is a risky thing to say with so many
kinds of racing and different racing fuels.

For example, Formula 1 cars run on plain old pump gasoline, but they
rev toward 20,000rpm if not higher.

Their "racing fuel" is the same stuff you can get at a gas station
although someone is paying a LOT more attention to the quality of
every liter used in an F1 car. They are not allowed to use octane
boosters or additives.
 
PMDR said:
"Racing fuel is always ...." is a risky thing to say with so many
kinds of racing and different racing fuels.

For example, Formula 1 cars run on plain old pump gasoline, but they
rev toward 20,000rpm if not higher.

Their "racing fuel" is the same stuff you can get at a gas station
although someone is paying a LOT more attention to the quality of
every liter used in an F1 car. They are not allowed to use octane
boosters or additives.
Click to expand...

OTOH, Indy cars burn methanol, which naturally has a very high octane
rating.
 
Just to get it straight......higher octane ratings DOES NOT mean
slower burn time, it means that the gas can withstand higher heat and
pressure before an uncontroled explosion. The only to use high octane
is to help prevent pinging and detonation in high compression and
forced induction engines. Racing fuel is always above 100 octane, and
some is as high as 140. This would not work at 8000 rpm if it was a
slow burn time. For the problem with the Elantra, check the cat. it
may be cloging. If it is, the back pressure would cause more heat and
detonation. The problem would be amplified a high rpm or under a heavy
load, like going up a hill. Higher octane may help a little, but I
don't think it will solve the problem. Get it checked out soon.
Detonation and pinging will ruin your engine.
Bill
Click to expand...

Hi,

Could you please tell me what "cat" is? Catalytic Converter? thanks
so much!
 
Brian said:
OTOH, Indy cars burn methanol, which naturally has a very high octane
rating.
Click to expand...
Not to argue the point but my impression is that methanol has a lower
octane rating than does regular gas.
 
James said:
Not to argue the point but my impression is that methanol has a lower
octane rating than does regular gas.
Click to expand...

Nope. Both Ethanol and Methanol have much higher octane ratings than
pump gasoline.
 
Please allow me to correct myself before I take any more hit on this.
When I said "always over 100", I should have said "almost always", and
I was refering to petrolium basd gas. My appologies.
Sorry Bill, but that's incorrect. Racing fuels only work efficiently in
very high compression engines, or those that are highly boosted through
turbocharging or supercharging. The extreme heat and pressure created by
the high compression and/or boost cause the high octane fuel to burn
faster than it would in a lower compression engine. The burn rate of a
given fuel is a function of heat and pressure, it's not constant.
Click to expand...
On this I will agree to a point, but lower octane fuel that is put
into high pressure situation of the race engine will ignite from the
heat and pressure alone and not by the spark as it should. That is
what I am talking about. I should have explained myself better.
A clogged cat generally just causes a loss of power. I've never heard of
one causing detonation and if you think about it, it seems pretty
unlikely. High backpressure prevents exhaust gasses from exiting the
cylinders efficiently. Exhaust gas that isn't expelled has the effect of
reducing combustion temperatures, which is why engines used EGR
(Exhaust Gas Recirculation) systems to reduce combustion temps (which
reduces the formation of certain pollutants)
Click to expand...
On this point, I have seen it happen more than once. I have seen a
clogged cat. turn an exhaust manifold cherry. The EGR is only open
when there is almost no load on the engine, and is considered an inert
gas, so it doesn't burn again and causes less heat. It is in a loop-
back configuration and is not causing back pressure.
That's typical of knocking/pinging problems in general.
Click to expand...
agreed, but this could make it worse.
Definitely.
Click to expand...
;)
 
"Racing fuel is always ...." is a risky thing to say with so many
kinds of racing and different racing fuels.

For example, Formula 1 cars run on plain old pump gasoline, but they
rev toward 20,000rpm if not higher.

Their "racing fuel" is the same stuff you can get at a gas station
although someone is paying a LOT more attention to the quality of
every liter used in an F1 car. They are not allowed to use octane
boosters or additives.
Click to expand...
Sorry, I should have said almost, just as you should have. Formula 1
cars run on plain old pump gasoline but with some addatives
likeToluene which makes the octane rating shoot way up.
 
James said:
Not to argue the point but my impression is that methanol has a lower
octane rating than does regular gas.
Click to expand...

Impressions are nice, but facts are better. Your impression is wrong.

Matt
 
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