I need a lesson about octane.

[shadow88]

Overall, this is a fuel question and discussion.

Can anyone shed some light on the difference between "motor octane" and "reserch octane"? What comes out of the pumps? What comes out of the sealed drums you buy at the speed shop?

Also any input regarding oxygenation and the correct air/fuel adjustments required would be very helpful.

[t3rse]

Pump gas octane is boasted because of the ethanol content. However you need to richen it up a tad due to the ethanol. A true high octane gas such as c16 can be run leaner to make more power before detonating. I tuned to around 12.0 with c16. With pump gas you have to tune much richer, not only because of the ethanol content, but because you need excess fuel to cool things down to prevent detonation. That said, I also tune e85 to around 12.0. Pump gas I would shoot for 11.5 to 11.2. Gas pump octane is boasted with ethanol...race shop octane will be more accurate but some special race fuel blends don't like boost, so do your research.

[zin]

Overall, this is a fuel question and discussion.

Can anyone shed some light on the difference between "motor octane" and "reserch octane"? What comes out of the pumps? What comes out of the sealed drums you buy at the speed shop?

Also any input regarding oxygenation and the correct air/fuel adjustments required would be very helpful.

Research Octane is the number obtained by running a fuel in a special, variable compression ratio engine. A research engine as it were.

Motor octane is the number obtained by actually running the fuel in a road car.

Motor octane is the better one to rely on vs research, however, most ratings are of the R+M/2 method, whereby they add the two together and divide by 2 to get an average of the two ratings...

What you buy in a drum is going to be held to higher standards that what you get from a pump. Note that this just means you'll get what they say it is, that doesn't mean their 87 octane would be better than pump 91, just that it would be more consistent. This is helpful if you are doing engine development and want to remove as many variables as possible so your results are clear.

Keep in mind that octane is the rating of the fuel's resistance to detonation, but there are other factors such as burn rate, which is often related to it's specific gravity... Generally, a higher SG means a slower burning fuel. SG will also affect the tune due to it's effect on the lb/hr of fuel delivered via the injectors. As an extreme example, if the injectors were flowing lead instead of fuel, the pounds of "stuff" coming out of them would be much higher, even thought the volume doesn't change. Since engines are tuned on a lb of fuel to lb of air ratio, you can probably see how changing the SG of a fuel can skew the A/F ratios/tune.

Now that I've likely over-explained a simple concept, I'll leave you all in confusion!

Mike

[shadow88]

Actually, the R+M/2 I see at the pumps make far more sense now.

Say, sv-05 from VP fuels has a motor octane rating of 98 but reserch octane of 106....... If that were at the pumps it would be 102? I'm just trying to get a feel for how slowly I need to tune this stuff in. I will be taking it slow.

Also it mentions a 4.7% oxygen content. Should I aim 1/2 point richer because of that? More? Less?

Spec sheet here.
SPECIFICATION SHEET FOR SV-O5

(Typical Values) Specific Gravity: .745 @ 60°F

Lead Content: 0 g/gal (US)

Oxygen Content: 4.7 %

Color: Clear

Motor Octane: 98

Research Octane: 106.0

Reid Vapor Pressure: 3.50

Distillation:
10% evap @ 185.4°F

50% evap @ 208.6°F

90% evap @ 216.3°F

E.P. @ 225.7°F

Production: Elmendorf, Texas USA

Availability: Sealed Drums

Rev: 07/00


This is $20 more per 5 gallon drum. I'm willing to spend it, just not sure if I'll be able to take full advantage of it.

Vp fuels MS-109
SPECIFICATION SHEET FOR MS 109

(Typical Values) Specific Gravity: .722 @ 60°F

Color: Clear

Motor Octane: 101

Research Octane: 109

R+M/2: 105

Reid Vapor Pressure: 6.17

Oxidation Stability (min.) 1440+

Distillation:
10% evap @ 147.0°F

50% evap @ 167.8°F

90% evap @ 213.3°F

E.P. @ 263.8°F

Production: Elmendorf, Texas USA

Availability: Sealed Drums

[69viper]

:I used to work at a refinery testing the octane of gasoline, cetane for diesel and performance number for aviation fuel. I can still hear the knocking!

Octane numbers are obtained by running the fuel in 2 laboratory engines.
Research Octane is run on the RON engine. It is used to simulate ideal conditions. Runs slower 600 rpm and the intake is cooler (120 F)
Motor Octane is run on the MON engine.
It simulates non ideal conditions. Runs at 900 rpm and the intake has a heater that controls the intake temp at 300F.

Octane is all based on assuming that iso-octane is 100 octane and n-heptane is 0 octane. Standard fuels are made in varing combinations of these 2 compounds. The standards are then run with the fuel that your trying to determine. The engines have a knock sensor that is connected to a knockmeter. The octane is calculated by how much your sample fuel knocks compared to your standards.



A fuel with a MON and RON that are close together is a better fuel than one with a wide range fuel. You also need to look at the distillation because it shows what size of hydrocarbons are in the fuel. The higher the temperatures then the larger the hydrocarbons in the fuel. Large hydrocarbons produce more BTUs thus more power.

The MS-109 looks to be the better fuel since it has the higher MON and the end point of the distillation was 263 degrees. If your running 20 psi of boost then this fuel should work well for you. I'd tune for an air/fuel ratio of 11.5

Just remember that a high octane fuel burns slower and thus burns more complete. You want to use the lowest octane possible that won't cause detonation in your engine. Most people just use the highest avaliable octane just to be safe.

Probably more info then you wanted.

[OmniLuvr]

Just remember that a high octane fuel burns slower and thus burns more complete. You want to use the lowest octane possible that won't cause detonation in your engine. Most people just use the highest avaliable octane just to be safe.

so glad you brought this up, because some people dont get it. the lower the octane the more power is released at a given time, thus giving you more power (to a point). like you said, you want to run the lowest octane rating you can get "away" with, but it also doesnt hurt to be safe.

the funniest dyno comparrison ive seen (well not literally) was in like super street magazine. they had the new r35 skyline on the dyno, put air filter then dyno, intercooler tubes then dyno, then exhaust. finally they got all excited to dump some c16 in the pig to "make more power" and after that dyno session, they actaully made 3 peak hp less than stock configuration. this was obviously without a tune, which im sure would have netted them more power by increasing timing and maybe making it a bit leaner.

also, i believe, that when they test octane its at a specific a/f ratio, am i correct? so if you increase the amount of fuel flowing into the engine, you will reduce combustion chamber temps, reducing the chance of detonation, therefore increasing the octane rating of the fuel in "your" engine.

then you can get into alch/meth/e85 awsomeness. alky is a little more then half as powerfull as gasoline, but you can make almost twice a much power with it because of combustion chamber cooling effect when running at least twice as much fuel. my friend made 48 more hp in his c5 zo6 vette when he changed from 65% c16/91 pump gas to e85. of coarse these gains were realized with a change in his tune, injectors and hours on our friends dyno, but this was also a stock longblock from t-body to exhaust manifolds.

[BIG PSI]

Great write up guys..........

Chuck

[janus]

Now that I've likely over-explained a simple concept, I'll leave you all in confusion!

not at all, thanks for sharing although i was already aware of the stuff behind and RON, MON, AKI.. just the issue about specific gravity is news to me and was interesting.
btw, if you guys ever visit europe, we use RON here at the pumps!

[thefitisgay]

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[shelbydave]

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[Spraynlog]

so glad you brought this up, because some people dont get it. the lower the octane the more power is released at a given time, thus giving you more power (to a point). like you said, you want to run the lowest octane rating you can get "away" with, but it also doesnt hurt to be safe.

the funniest dyno comparrison ive seen (well not literally) was in like super street magazine. they had the new r35 skyline on the dyno, put air filter then dyno, intercooler tubes then dyno, then exhaust. finally they got all excited to dump some c16 in the pig to "make more power" and after that dyno session, they actaully made 3 peak hp less than stock configuration. this was obviously without a tune, which im sure would have netted them more power by increasing timing and maybe making it a bit leaner.

also, i believe, that when they test octane its at a specific a/f ratio, am i correct? so if you increase the amount of fuel flowing into the engine, you will reduce combustion chamber temps, reducing the chance of detonation, therefore increasing the octane rating of the fuel in "your" engine.

then you can get into alch/meth/e85 awsomeness. alky is a little more then half as powerfull as gasoline, but you can make almost twice a much power with it because of combustion chamber cooling effect when running at least twice as much fuel. my friend made 48 more hp in his c5 zo6 vette when he changed from 65% c16/91 pump gas to e85. of coarse these gains were realized with a change in his tune, injectors and hours on our friends dyno, but this was also a stock longblock from t-body to exhaust manifolds.

E85 also works great in our cars, since it increases exhaust flow and spools the turbo quicker, not to mention the detonation protection. 14-15 lbs of boost can be run without an intercooler with no problems.

[thefitisgay]

dont you need corrosion resistant lines and such for e85

[Spraynlog]

dont you need corrosion resistant lines and such for e85

That was more of an issue with methanol. I did replace all the rubber fuel lines with flex fuel compatible ones, they are available from NAPA. I have had E85 in the car now for about a year, no corrosion issues so far.

[Captain Chaos]

Here's a simple explanation. Understand this is from a stock superstock racer using carburetors. Some examples and tests may not be wise for later model and boosted applications, but the principals of fuel is similar.
http://www.dvorakmachine.com/tech_WhatAboutFuel.shtml

[Dusty_Duster]

Pump gas octane is boasted because of the ethanol content. ...

Wrong. 87 octane is 87 octane, even if it contains 10% ethanol. Otherwise, it would be a violation of federal standards.

When a gas station sells 10% ethanol fuel, they purchase LOWER octane and mix in the 10% ethanol to produce the desired octane. (For example, mixing 90% 85-octane and 10% 129-octane pure ethanol produces right around 89 octane.)

The problem here is that ethanol breaks down at a different rate than gasoline. (Octane decreases as fuel gets older.)

EDIT: Here is the calculation

85 * 0.9 + 129 * 0.1 = 89.4