87 Octane, this is really what everyone uses...

LazyBastard said:
This whole "burns cooler" thing is a big lie.
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LB, it's not burning cooler like you said, it's burning slower. Same thing can said about the colder heat range spark plug. It too also slows the burn down.

Some simpler terms...for Octane...from the internet..
The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting

SledFreak said:
On the dyno, 93 made the Apex lose Power... You figure it out...
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Did you witness this? Or is this hearsay?
 
LazyBastard said:
Dude... *I* know that, he didn't, which is why I said that "burns cooler" is a lie. And it follows from burns SLOWER that the heat will be out of the combustion chamber and into the valves and exhaust pipe.
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Sorry for 're-iterating'!!
 
bottom line ....we all know..use 87 octane ...for various reasons...it works...and nothing will work better on a stock engine..
 
further clarification...

octane additives are added to fuel to DELAY or slow the burning process of the fuel to allow the piston to compress further (when needed) for a higher compression engine...(ours is a lower compression engine)...an example of one in need is a not normally aspirated engine...read turbo,supercharger with lots of added boost..

these higher compression ratios ...or boost added,raise the possibility of pre-ignition or detonation...both negative...but different .... similar in they can be caused by the fuel igniting too fast or at the wrong time from the high compression or boost ......or heat built in (again higher compression raises the cylinder heat)

on a lower compression motor these anomalies do not usually take place and the additive that raise octane to slow the burn actually HINDERS the proper time for the fuel to be burned and a performance loss is incured.
 
My understanding is that it is a compression issue. Not the speed in which it burns. You are trying to keep the fuel from self-igniting under compression.

Higher octane fuels have less btu’s (i.e. power) than lower octane fuels. Think of diesel fuel compared to gasoline.

The compression ratio of the engine determines the octane you need to run. Higher octane fuel does not make an engine run better unless you are experiencing knock.
 
Not quite.
Yes, you pick it based on the compression ratio, but it works as follows;

High pressure = high heat.
High heat = fast combustion.

Now we don't want fast combustion. We also don't want slow combustion.

When the high compression causes fast combustion, we take a slow burning fuel and end up with a normal combustion.



Regarding the amount of energy stored in fuels; high octane fuel *should* store more energy, however, when the high octane rating is caused by the addition of combustion inhibitors, this is not the case.

The fuel is made of single-strand hydrocarbon strings, ie HYDROGEN and CARBON atoms joined in all single-electron bonds. In the case of gasoline, it is primarily made of OCTANE molecules, made of 8 carbon atoms (hence "oct") and 18 hydrogen. Methane is 1 carbon and 4 hydrogen. Diesel, on the other hand, would be about 12 carbon, 26 Hydrogen. The amount of energy stored in each molecule is a product of the number of electron bonds (actually a little more complicated, but this is suitable for this discussion). There is one bond for each Hydrogen-Carbon bond, and one bone for each Carbon-Carbon bond, ie Octane = 25 bonds, Diesel = 37.

Now the *correct* way to get high-octane fuel (I wish they didn't use this term, its not appropriate), is to use an increased average length of carbon chain, and hence more energy.


Of course, if it doesn't burn completely, it doesn't matter if it stores more energy. All it does is increases the vehicles hydrocarbon emissions -- ie, very bad for the environment, if you are concerned about this.
 
Just gotta say, the second I finished reading this topic they started discussing the exact same topic on tv.
All good info. Organic Chem does have a purpose after all.
 
I am running my Apex with the head gasket split and the timing advanced 5 degrees this year. What should I run? 93?
 
Charged RTX said:
I am running my Apex with the head gasket split and the timing advanced 5 degrees this year. What should I run? 93?
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first issue is the boost..whoevers kit this is contact them.... you'd want to calc your new compression ratio..(this can easily be done...contact tim@sledehdz.com or go to his forum and he can help you calc).....tell whoevers turbo kit your adjusted compression ratio and timing advance

the timing advance should build quite a bit more heat into the engine..adding up the boost, timing advance and higher compression I'd be concerned about octane and engine temp/cooling..

even at low boost...I know I'd be concerned if 93 was called for and I was stuck in the back forty with some aged gas..not really gettin the 93 ya know..

I have a secret sauce for highly adjusted sleds to help in these cases...p.m. me if need be..


either way..what about a parker knock box as a back up security?
 
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