gasoline
- Thread starter tommyB
- Start date
87 octane. the short story is: higher works but detonates slower possibly robbing power. busa is tuned for 87 or above per street use - common gas use. this is a debated issue for many. so try what you want and use whatever DOESN'T go 'PING!' higher can leave burnt carbon buildup in your engine too. all this comes from my months of research, reading, posts, etc. now that I have a feel for mine, I'll be trying a tank of 92, then 100 octane and see if anything is differnet. the 100 is 3.95 a gallon here or more so it BETTER make Busa stand up and sing showgirl tunes 
Unless you are running a high performance motor or Turbo 87-91 is fine. 87 works great on a stock Busa. Just one caution gas is different in each state, so use what works for you. Lots of gas is oxygenated so the readings are a little harder. what this does is makes it easier to burn which can be bad in some cases.
No need for anything higher than 87 unless you have raised the compression ratio from stock. High octane levels are only needed for high compression engines.
To spare the long explanation of what octane is and what it does know this, gasloine has an allowable range of lengths of carbon chains that can it can comprise. However, octane is more stable at higher pressure than other length carbon chains. So if you run relatively low octane gasoline like 87 in a high compression engine it tends to ignite on its own due to the pressure increase before the piston reaches TDC (before the spark plug would normally ignite it) causing an audible "knock" sound and can lead to major damage such as bent valves etc.
Long story short, a stock Busa is considered standard compression and can be run on standard 87 octane gas.
BTW, the higher the octane rating number, the higher the ratio of octane is versus the remainder of the carbon chains in a particular gasoline. And yes octane is 8 molecules long (hence the "oct" latin prefix). Similar simple compounds that are actually different length carbon chains include propane, butane, methane, etc. Bet you didn't know that the difference between octane in gasoline and propane in your grill is the length of the carbon chain. Cool huh? And these are all "distilled" or refined out of crude oil along with motor oil etc. etc.
To spare the long explanation of what octane is and what it does know this, gasloine has an allowable range of lengths of carbon chains that can it can comprise. However, octane is more stable at higher pressure than other length carbon chains. So if you run relatively low octane gasoline like 87 in a high compression engine it tends to ignite on its own due to the pressure increase before the piston reaches TDC (before the spark plug would normally ignite it) causing an audible "knock" sound and can lead to major damage such as bent valves etc.
Long story short, a stock Busa is considered standard compression and can be run on standard 87 octane gas.
BTW, the higher the octane rating number, the higher the ratio of octane is versus the remainder of the carbon chains in a particular gasoline. And yes octane is 8 molecules long (hence the "oct" latin prefix). Similar simple compounds that are actually different length carbon chains include propane, butane, methane, etc. Bet you didn't know that the difference between octane in gasoline and propane in your grill is the length of the carbon chain. Cool huh? And these are all "distilled" or refined out of crude oil along with motor oil etc. etc.
StealthBus
Registered
EAK you and I could really have some fun with this octane business, thermo was a killer in college but it's hellafun to talk about now!
I've had best results from higher octanes here in the mountains....blame it on the heat in the summer, altitude, humidity, whatever.....don't agree with the carbon buildup statement somebody made about higher octanes...but then again I've only been an aircraft mechanic for 9 years...we always used 100+ in the little ones.
all brands are not equal either....exxon sucks! my mustangs, sho, bikes...none run right on exxon....they all get the low rpm studders from it....never get the studders with shell
I've had best results from higher octanes here in the mountains....blame it on the heat in the summer, altitude, humidity, whatever.....don't agree with the carbon buildup statement somebody made about higher octanes...but then again I've only been an aircraft mechanic for 9 years...we always used 100+ in the little ones.
all brands are not equal either....exxon sucks! my mustangs, sho, bikes...none run right on exxon....they all get the low rpm studders from it....never get the studders with shell
All true and very well said except for High octane for high compression rations. You can have a low comprssion engine 8:1 and put a Turbo on it. That changes the whole equation. Turbo='s need for higheer octane to burn slower and eliminate pre-detonation. Although tech. you are still correct because a turbo is raming compressing more air.
Yeah, I am sure you are correct Ninja Eater. I have no experience with turbos only read about them and it would make sense that any forced intake (turbo, supercharger) would require higher octane to prevent predetonation, particularly if you did not have an intercooler of come sort.
I need to learn more about turbos.
And to think I went to community college. What can I say, I read alot and retain technical info. That is why I became an engineer. But please know that I am not an expert. Just repeating what I have read and learned from experience.
I need to learn more about turbos.
And to think I went to community college. What can I say, I read alot and retain technical info. That is why I became an engineer. But please know that I am not an expert. Just repeating what I have read and learned from experience.
SierraFlyer
Registered
Higher Octane will help reduce detonation (pinging). It will also burn slower than lower octane gas in the combustion chamber resulting lower peak cylinder pressure and LOWER horse power. Also you need to start the fuel burning a little sooner to get all the energy out of it, so higher octane gas needs a couple of degrees more total advance. The rule of thumb is to find the gas that has the LOWEST octane that won't ping in your engine. With appropriate timing you will get the most HP of all the fuels available. Detonation can be reduced by cooling the in-coming air (intercooler), reducing compression ratio, reducing boost on boosted engines, running a cooler sparkplug (hot ignition point) and even running a cooler thermostat to get residual heat out of the head can help a little. Car racers will even smooth off sharp corners in the combustion chambers and pistons to remove hot spots that can ignite the fuel mixture before the sparkplug fires.
Interesting points all, especially the carbon chains. At the risk of sounding like a hair-splitting jerk, I am "compelled" to add a comment. As suggested above, high-octane or "premium" gas burns slower than low-octane or "regular" gas. Therefore, combustion is slowed with premium gas. Slower combustion can prevent pre-ignition, or "pinging". Pre-ignition is ignition of the fuel/air mixture before the spark plug fires. The ping of pre-ignition sounds like marbles bouncing around inside the engine and it is usually relatively harmless. The terms "pre-ignition" and "ping" are sometimes incorrectly used interchangeably with "detonation". The death rattle of detonation results from an erratic and intense pressure wave that occurs shortly after TDC (top dead center) of the power stroke. When the air/fuel mixture is ignited by the spark plug, a combustion flame front spreads outward from the plug accompanied by pressure waves created by the combustion. Detonation is caused by the amplification of two pressure waves combining to form an intense wave "spike", which then bounces around the combustion chamber surfaces, causing very-high temperature spots that ignite a second flame front. The "heavy knocking" sound of detonation results from this secondary ignition and it's pressure waves which greatly shock-stress the pistons, piston lands, rods, crank and bearings. Schlieren photography of combustion chambers during actual engine operation has revealed that detonation is not the result of "colliding flame fronts" as some believe. Most everyone does agree, however, that severe detonation will quickly destroy an engine.
There, now I feel better.
There, now I feel better.
Pimpbike
Registered
I tried to tell someone that one time and all they could come up with is..... Why do Race cars and planes use jet fuel or real high octain fuels? Why do they make octain boosters for fuel? If you get more horse power out of lower octain fuels then it doesn't make since. Please help.....
-Pimpbike
-Pimpbike
Different engines have different octane needs due to a variety of reasons, some of which were mentioned above... compression, superchargers, fast-burn combustion chambers, fundamental mechanical design, etc. Let's say every engine needs "X" amount of octane. The value of "X" can vary considerably because of the differences mentioned--compression, supercharger, etc. Once an engine's "X" value is met, that amount of octane is ALL it needs. Anymore octane is just a waste of money and might cause power losses due to slowed combustion processes. Some engines NEED 100 octane because they are mechanically tuned to high power output levels ("race" engines) because of forced induction, compression, etc. . Does that make sense?
CorrodedAlien
Registered
Look at ther poll I posted in the Poll section about this subject and you will see how many believe the High Octane is best myth...
Pimpbike
Registered
So there engines are made for higher performance so they need the higher octain. Not that the higher the octain the better results but the engine needs that higher octain to function at peak performance.
So if that is correct then you could end up putting to high of an octain in say a racing bike and it not put out as well as it would with the lower octain.
Does that make since?
???
So if that is correct then you could end up putting to high of an octain in say a racing bike and it not put out as well as it would with the lower octain.
Does that make since?
??? An Afterthought: There are times during modifications/tuning when it may be prudent to run higher than needed octane just to be safe because detonation will KILL an engine right now. Once "tuned", one could then start backing-off of octane point-by-point until carefully finding that "needed" amount. I am not suggesting that everyone run out fill up with 87 octane. I suppose most guys run 91 or 93 in stock engines for the above reason--to be safe. That's not a bad thing. Sometimes I do it too. Any performance loss from excessively-slowed combustion (higher than needed octane) would probably be hard to measure at the street tuning level, except, maybe with some of the bad ass turbos. I've seen guys go to the drag strip and fill up on 110 octane racing gas for their stock engine with headers and a K&N filter and then wonder why they lost performance and blame it on the humidity, temperature, moon phase, or whatever. The diff between 87 and 92/93 is small. The diff between 87 and 110 is not. :tounge:
Deputy
Registered
"High octane levels are only needed for high compression engines."
After reading that I had to run in the bedroom and drag out the service manual for some specs. Unless they have lowered the compression ration from 1999, it's 11.0-1. That's pretty freaking high in my book. The service manual also states
"FUEL-Gasoline should be graded 91 octane (ROM) OR HIGHER."
Think I'll stick with what Suzuki recommends and let other guys experment with low octane gas.
Dep
After reading that I had to run in the bedroom and drag out the service manual for some specs. Unless they have lowered the compression ration from 1999, it's 11.0-1. That's pretty freaking high in my book. The service manual also states
"FUEL-Gasoline should be graded 91 octane (ROM) OR HIGHER."
Think I'll stick with what Suzuki recommends and let other guys experment with low octane gas.
Dep
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