octane and race fuel

[n_23_s]

I want to know the true story behind race gas. I know that higher octane will reduce detonation. Why does some people I talk to say don't run too much because it will cause my engine to run hot. If higher octane ignites harder how the hell will it make it run hotter? Has anyone heard anything about oxygenated racing fuel. Does it really make that much of a diffrence? thank you

[transzex]

the higher octane gas burns slower, sometimes so slow that it burns the exhaust valves as the gases are exiting the cylinder.

I've yet to need anything other than pump gas, even with a 85 shot of nitrous.

[n_23_s]

thanks for the good info that actually make perfect sense

[BseriesKllR]

most of the time higher octane gas makes people think there car is faster but tis all in there head....in some cases cars do need the higher octane gas but most street cars dont.

[ametzzz]

if i have 10.5-11 to 1 compression... will i need 89 octane or 87

[1point5crx]

i would stay away 87 with that compression,89+

[transzex]

depends how his timing/fuel maps are set......as with the intial timing.

[shadowboy]

higher octane gas does not necessarily burn slower, faster, hotter, or colder than lower octane gas.

the octane is a measure of AUTOIGNITION temperature.

in other words the fuel with higher octane rating will require a higher temperature to self-ignite (ignite a flame front with no spark).

detonation is nothing more than autoignition. it has nothing to do with burn speed or burn temperature. in fact, methane burns faster than gasoline. it also has a much higher auto-ignition temperature (read: burns faster, higher "octane" rating)

here (http://imartinez.etsin.upm.es/dat1/eCombus.htm) is a link containing properties to many different fuels.

on this list you will see the 2 fuels that are the reference standards for the octane ratings you see on gas, these are n-Heptane, or i-Octane (or iso-octane).

n-Heptane has an octane rating of 0
i-Octane has an octane rating of 100.

notice the relationship of these two fuels to autoignition temperature
n-Heptane (0 octane rating) will self-ignite at 422 degrees Faranheit (490K(
i-Octane (100 octane rating) will self-ignite at 782 degrees Faranheit (690K)

big difference. the way the octane rating scale works, is that 89 octane gas has the same detonation resistance (autoignition temperature) as a mixture containing 89% i-Octane, and 11% n-Heptane.

the burn speed is irrelevant, in fact, both fuels have a deflagration speed (flame front speed) of 40 centimeters per second.

by comparison, natural gas has a deflagration speed of 45cm/second (faster than gasoline), but it has an auto-ignition temperature of 1,070 degrees F

[sohc_mshue]

you want to run the lowest octane gas possible that you can run without detonating to achieve the best performance.

[shadowboy]

running a higher octane gas won't hurt performance. it just costs more with no benefit ;)

[D15VtecLessCr-x]

:idea: very interesting topic...

I have been told to use 93 octane... only cuase it saves the engine and burns cleaner... and for high compression engines like mine.

I know for a fact that if i do know put 89 octane... my car WILL infact misfire. I have gotten my motor used to using 93 at the pump that it will not take 91 or below...

[shadowboy]

motors don't "think," they don't get used to any given fuel, so to speak.

if you have misfiring problems at 89 octane it is probably just because the octane rating is too low. carbon build-up in the combustion chamber perhaps?

the "use 93 octane because it burns cleaner" is about as valid as the "engine brake when going down hill to save your brakes argument"

it was once true that premium fuel had detergents that make an engine run cleaner, but nowadays most fuel companies add those detergents to all octane ratings due to the prevalence of fuel injection these days...

http://www.cartalk.com/content/columns/Archive/1994/June/14.html