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"Octane for dummies"

49K views 75 replies 41 participants last post by  Sixpack577 
#1 ·
http://en.wikipedia.org/wiki/Octane_rating


It also has links of the topic that relate to the octane. I know we've had many discussions in the past with octane, but this article and all of its links pretty much sums it all up.
 
#2 · (Edited)
Wikis can sometimes have some questionable or controversial information but the last time I checked their octane page it was in good shape. Looks similar if not the same now.


Good thinking RT, I think this deserves a sticky.


IF YOUR RAPTOR IS INTERNALLY STOCK AND YOU'RE NOT USING FORCED INDUCTION OR NITROUS THEN YOU SHOULD NOT BE RUNNING RACE GAS.
 
#4 ·
Just reading and thinking (never at the same time, that's dangerous).

"Octane number is the number which gives the percentage, by volume, of iso-octane in a mixture of iso-octane and normal heptane, that would have the same anti-knocking capacity as the fuel which is under consideration. For example, gasoline with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90. [1]"

What about avgas that is over 100, like 110LL?
 
#39 ·
WELL if by av gas you mean aviation yes it does have a higher octane BUT it also contains things that help it burn at high altitudes and keep it from freezing being so high in the sky the air is thin and can get very cold so its a common misconseption that aviation gas is a good performance gas stick to klotz and vp for your race gas
 
#5 ·
Just need to keep reading a little:

It is possible for a fuel to have a RON greater than 100, because isooctane is not the most knock-resistant substance available. Racing fuels, straight ethanol, Avgas and liquified petroleum gas (LPG) typically have octane ratings of 110 or significantly higher - ethanol's RON is 129 (MON 102, AKI 116).


:thumbsup:
 
#6 ·
Ok call me stupid but some of that is a little confusing. Let's break it down and just let me ask everyone what they run in their Raptor's (no major engine work). I typically run 90+ in mine, but am I wasting my money?
 
#38 ·
i run 93 most of the time.shell is the best.
 
#7 ·
For internally stock Raptor 660 atvs;

As a general guideline the vast majority bikes with proper jetting and limited extreme situations can run 85-87 octane which is typically considered "regular" pump gas.

Some people can experience pinging/pre-detonation/pre-ignition or whatever you want to call it with that octane but most of the instances I've come accrossed were a result of running too hot or other problems.

Low elevations combined with high temperatures contribute to the likelihood of pinging but very rarely are the sole cause, returning back to a possible problem with the bike itself.

Again this is all my opinion drawn from my experiences, but I don't see a reason why you'd need to run anything more than typical regular fuel in an internally stock machine.
 
#8 ·
Should have read past my nose. :lol:

I run 91 octane in my internally stock rappy. I ride in Glamis, Phoenix and Tucson without problems. For an extra buck per 5 gallons, i like being sure i have enough octane.
 
#10 ·
pewterpecker said:
Anyone here tried running e85 in their rappy? It's cheaper than race gas and has plenty of knock-resistance to boot. All you would need to do is increase the fuel flow a bit to make up for the lower BTU's.
Ethanol is 116 octane, E85 is much lower.

E85 would require more than just bigger jets, but also a water separator (or very careful storage) and the fuel system would need to be protected from the corrosive properties of the alcohol. Basically you'd need a similar procedure to run E85 as you would for running alcohol.

E85 has a signficantly lower specific energy than regular grade pump gasoline, it's only about 70% as potent. In other words I wouldn't recommend it.
 
#12 ·
This came out of the article, u say 9.2:1 stock will run on 87octane and u tell me that my 11:1 doesnt need hight octane, well it says 104, i know temp elevation will effect it but, what were u guys trying to tell me, i just need it explained



Compression Octane Number Brake Thermal Efficiency
Ratio Requirement ( Full Throttle )
5:1 72 -
6:1 81 25 %
7:1 87 28 %
8:1 92 30 %
9:1 96 32 %
10:1 100 33 %
11:1 104 34 %
12:1 108 35 %
 
#13 ·
those are static numbers, in reality when your motor is running a 11:1 with a cam its actually pushing out around 8:1 to 9:1 at the most. so for your 11:1 static it should run (8:1 dynamic) or so. which means you should only need 92-93 or so octane..find 94 and 11.5:1 is likely, run a very aggressive cam with high flow porting and its possible to run a 12:1 on 94 octane (which is still pump in most states, sunoco). Every motor is different, therefore requires a different dynamic compression. although static compression remains the same regardless.
dynamic comp. for a 9.2:1 is around 7:1
 
#18 ·
kal1fornia said:
will running a higher octane rating in your atv help the engine last longer and perform better?
Your atv will be most reliable and perform best when it gets just enough octane to keep it from pre-detonating/pinging, no more and no less. If your bike runs right on 89 you're not going to gain any benefit by using a similar fuel with higher octane.
 
#37 · (Edited)
best statement in the entire writeup. My car for example is 12:1 28* of timing and runs great on 93, and if I ran race gas I would lose power unless another factor is changed ie timing. Just run what is right for your setup if you know damn well you should only run on 104 then run on 104 etc.
 
#21 ·
Hi peeps

I am form South Africa and only recently found your site and I must say found a lot of info on issues I had. Especially with the limiter in reverse.

Now we have 93 and 95 unleaded at the pumps at R7.00/l = that would be like $1.00/l :crazy:

what would you say I use then??? :3question:

Keep up the good work!!! :thumbsup:
 
#22 ·
US gasoline octane numbers are reached by the (R+M)/2 formula while much of the rest of the world uses RON (Research Octane Numbers) alone meaning that a gasoline in a pump in the US would have a lower number on the sticker than identical fuel in a pump outside North America.

The vast majority of discussion you see on here about octane and compression will be using the US equation for octane ratings so just remember that our 93 octane may not behave the same as your 93 octane.
 
#23 ·
Mad Dog said:
US gasoline octane numbers are reached by the (R+M)/2 formula while much of the rest of the world uses RON (Research Octane Numbers) alone meaning that a gasoline in a pump in the US would have a lower number on the sticker than identical fuel in a pump outside North America.

The vast majority of discussion you see on here about octane and compression will be using the US equation for octane ratings so just remember that our 93 octane may not behave the same as your 93 octane.
Mad dog, do you know the comparison between AV gas Octane and Octane ratings for land vehicles
 
#25 ·
Yes Av gas is more consistent but it is formulated to burn longer. This could cause serious heat problems in some engines. Lead may also be a problem. 100LL (Low lead) has more than twice the lead automotive fuel has and could cause buildup problems. Aviation have different timing and clearance specifications and compression ratios than quad engines. In most cases Av gas is not a good idea for small engines. Aviation fuel is designed for aviation engines.
(Got this of the previous posts email)
 
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