Race Gas Octane Calculation

[joshholmes20]

I just purchased some 110 octane race gas (named Koch Power 110) and I am wanting to mix it with some premium pump gas to get the octane levels down some for my stock motor. Is it safe to calculate octane ratings using the following formula?

Ex. For 40% Race Gas and %60 Premium
(.40*110)+(.60*91)=98.6 octane

Also, if anyone has a reccomendation as to what a desired octane rating would be for a 2003 YZ 125 with: stock piston/rings, stock reeds, Twin Air filter, FMF Fatty Pipe/Powercore II Silencer.

Thanks

 

[Okiewan]

... not sure why you want to lower it?

 

[joshholmes20]

I am thinking because the compression on the stock motor would not be suitable to run the high octane gas efficiently. If I am mistaken, please let me know. Also, It will save me some money ;) I have also heard that running too high of an octane fuel can be detrimental to performance if your motor is not set up to run. I have never looked at any data to back this up, merely what i've heard.

 

[Butcher-Boy]

My book for my 99 yz 125 says to use 95 or higher octane rating. I did try running 110 in my old kx 125 and indeed it did lose some noticable power. I'm in the same boat as you because the highest octane around here is only 92. I have'nt heard any pinging running pump gas but then again I really have'nt hammerd on it yet.

 

[burnht]

I don't really post if you're going who is this?; but i believe outside of minor changes to jetting, running higher octane gas than needed just protects against ping more than necessary. Kind of like overkill.
Unless i'm mistaken, it shouldn't hurt performance.

 

[Masterphil]

Mixing two fuels together and expecting to be able to calculate the octane is not going to happen. There is no formula for calculating the octane of some hodge-podge fuel combo.

Race fuel does not cause a decrease in performance on a properly jetted machine.

 

[joshholmes20]

Actually, I have had enough Chemistry to know that there is definately a way to calculate the exact octane rating of the "hodge-podge". However, I am sure it is not that simple to get an accurate count, but I would be willing to bet it's a pretty decent ballpark shot. I just wanted to check to see if that's how others figured it. Also, Masterphil, I understand correct jetting will make the bike run smoothly, however I do think too high of octane fuel without sufficient compression will indeed cause the bike to perform worse than it should.

 

[Rich Rohrich]

however I do think too high of octane fuel without sufficient compression will indeed cause the bike to perform worse than it should.

I guess you didn't have ENOUGH chemistry afterall. ;)

Octane numbers in excess of the engine's requirement will not hurt performance. BUTTTTTT, using a fuel with a distillation curve that isn't designed for the application whether it is a high or low octane fuel can have a negative impact on performance.

The octane rating of the fuel is probably the LEAST important specification for the average rider to look at.

In the case of the Koch Power 110, the performance drop you'll see running it straight (and you will likely see a drop) is due to the 90% and End Point temperature of the fuel's distillation curve being set to high. The end point is 320f which is way too high unless you are running in the desert or at really high outside air temps along with extended WOT runs. Mixing in pump gas won't fix this distillation curve problem. You need a fuel that has a lower percentage of heavy aromatic hydrocarbons so the end point will come down and that part of the fuel will be usable.

Fuels like Koch 110 & VP Red are designed for engines with more time and available heat in the intake to vaporize the fuel across the whole distillation range. These fuels would work well in a Big Block Dodge with a dual plane manifold peaking at 5200 rpm, but it's not the best choice for a small bore two-stroke.

This is closer to what you are looking for in terms of a distillation curve for a two-stroke.

Distillation (deg F)
0.01............108.2
0.05............141.2
0.10............154.2
0.20............174.5
0.30............192.7
0.40............204.8
0.50............210.4
0.90............223.0
0.95............230.5
<!-- / message --><!-- controls --> 0.99............266.8

Dr. David Redszus the blender of FirePower race fuels gave me these numbers as typical values at the refinery for Northern Illinois in the summer.
10% - 158.0
50% - 250.0
90% - 374.0
End point - 437.0

The EPA can provide the seasonal temp ranges for your area, but there are a couple of key points to remember. The EPA seasonal values only have to be met at the refinery not the pump. The 50% distillation temperature in Illinois (summer) has an acceptable range of 170-250F . Think about that. A single point on the curve can vary by a larger range than most race fuels change from 10-90%, and that is at the refinery point. By the time it gets to your engine the range is even greater. I have a fuel quality study done by American Automobile Manufacturers Association from a few years back. They did tests at the pump at a wide range of locations. I'll try to dig it up , but the basic point was what comes out of the pump is vastly different from the "numbers" the EPA quotes. The relative quality of pump fuel is really bad.

What I'm getting at is the idea that pump fuel won't undo a bad race fuel choice by combining the two.

 

[91kx]

Do you guys care to help the guy out or just make smart remarks?

 

[Okiewan]

Smart remarks are fun tho?

Seriously, there's no reason to dilute good fuel except to save dollars. Mix it half and half with some decent pump gas and you are good to go. You will end up with better fuel than from the typical pump. How much better (caluclated octane)? No idea.

The question remains... if he thinks race gas will make his stock motor run worse and wants to save money, why did he buy "race" high-octane fuel in the first place?

 

[Masterphil]

Correct me if I'm wrong, but octane is not a "calculatable" number. It is determined by running physical tests with a given sample of fuel and the number is "assigned". Rich, those numbers are crazy high compared to the fuel I'm using now:
Pump Sludge
10% - 158.0
50% - 250.0
90% - 374.0
End point - 437.0

Renegade 102
10%-150
50%-?
90%-222
EP%-250

It's really no wonder I'm running "leaner" jetting than anybody else riding in simular conditions/temp/altitude.

 

[joshholmes20]

I really appreciate all the good advice and help (sarcasm) I will try to keep my questions to myself from now on. The only one who had a decent thing to say was Rich, and I appreciate that. I will dump the 110 in the mower and try something new.

 

[joshholmes20]

I apologize for a post like this, but I felt I needed to vent after reading some of the replies to this thread I started. I have only had my eyes open to DRN for about 2 months, and have already made a fairly accurate observation IMHO. I have never seen an online forum with more potential to benefit more people than DRN in my life. I think you have a group of very knowledgable members here who are more than willing to help out in any way possible. The "founders" of this forum created it with no bias or prejudice to non-subscribers and are allowing anyone and everyone un-restricted access to a wealth of information. As you all can see I am not a member, but plan to be. Although there is more good information in these pages than most people could sort through in a lifetime, I have already seen too many threads that turn into pissing matches between users with over-inflated egos (perhaps due to the anonymity these forums offer to those who wish to stay that way). I urge you all to stay away from this because you have a REALLY good thing going here, and I hate to see when threads sometimes take a turn for the worse and you end up with bickering instead of healthy conversations with good insight. You can call all day long on the phone and never gain the knowledge about all-things-motorcycle that you can obtain here in a few minutes and a couple quick searches. Although joking and light-hearted humor can make for healthy comradery, it is the condescending remarks and smirks that sometimes take away from what I believe this forum was created for. Please keep this in mind, especially when attempting to help those (such as myself) who are merely looking to get answers to questions (as feeble as they might be) by which they have no other means of finding answers to.

 

[joshholmes20]

Back to my post. Octane rating, from what I've gathered, is based on the average of Research Octane Number (calculated by CHEMISTS) and Motor Octane Number (calculated by running the fuel in a standardized engine with an adjustable compression ratio, with the engine running at a certain speed and under load the compression ratio is increased until detonation occurs). The posted "pump octane" is the average of the two, the (R+M)/2 Method. From what I've read the RON is significantly higher than the MON. I've also gathered that Octane rating is merely a rating for the resistance that a fuel has to detonation.

Quoting from Marshall Brain from howstuffworks (dot) com: "The name "octane" comes from the following fact: When you take crude oil and "crack" it in a refinery, you end up getting hydrocarbon chains of different lengths. These different chain lengths can then be separated from each other and blended to form different fuels. For example, you may have heard of methane, propane and butane. All three of them are hydrocarbons. Methane has just a single carbon atom. Propane has three carbon atoms chained together. Butane has four carbon atoms chained together. Pentane has five, hexane has six, heptane has seven and octane has eight carbons chained together.

It turns out that heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot and nothing happens. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio."

From this information is where I got the idea that I could indeed use Chemistry to calculate the octane rating (being the RON), however I have no way of calculating the MON.

Rich, I found the standard distillation curve for Power 110 from their website racingfuels (dot) com:

IBP: 98
10%: 155
50%: 210
90%: 240
EP: 320 (all in deg F @ % evap.)

This seems to be a fairly suitable race gas if indeed these numbers are correct.

 

[Rich Rohrich]

From this information is where I got the idea that I could indeed use Chemistry to calculate the octane rating (being the RON), however I have no way of calculating the MON.

Unfortunately gasoline is made up of about 500 different chemical compounds so there is no practical way to calculate octane rating. Even if you knew the correct make up of the fuel, the different components don't always blend in a linear fashion and they can have antagonistic effects on octane when combined. Unless you are sitting in a lab at Exxon it's all just SWAG. ;)

Rich, I found the standard distillation curve for Power 110 from their website racingfuels (dot) com:

IBP: 98
10%: 155
50%: 210
90%: 240
EP: 320 (all in deg F @ % evap.)

This seems to be a fairly suitable race gas if indeed these numbers are correct.

It's a suitable fuel for my small block Dodge turning under 6000 rpm, but it's a poor choice for your application. The spike in temps at the end of the curve is too high for your use. That part of the fuel will just end up as carbon in the pipe and spooge, it's unlikely that it will burn in the chamber under normal circumstances.

 

[trial_07]

This is pretty deep stuff guys!!! Funny how a simple question can turn into a full chemistry lab report lol. Although thanks for the info, I found it interesting to read (even thought I missed some stuff).

 

[Masterphil]

This is pretty deep stuff guys!!! Funny how a simple question can turn into a full chemistry lab report lol.

I'd rather have the information as to why, rather than just getting a simple yes/no answer to the question. You could come on a site like this and ask Rich about every fuel you can think of, or he could give you a general guideline of the specs to look for and you could do it yourself. Which one would you rather have? An answer, or knowledge?

 

[trial_07]

Knowledge of course! Don't get me wrong this is not what I meant. I was just making one of those stupid comments that no one really needs (joking I think it's called).
Anyway sorry if you interpreted this in a negative way.