Noob Octane question

[wildsailor]

This is absolutely right.

Octane is actually a fuels resistance to burning. The higher the octane, the LESS it wants to burn (or ignite, more specifically). Most people don't understand this.

Most cars, timing is set and doesn't move. Use the lowest octane it will run. Usually manufacturers recommendation unless tuned. Which means higher octane is less power if timing doesn't change.

However, the mustang adds timing until knock is sensed. More octane yields more timing which yields more power. So higher octane means more power and more efficiency.

^^^^ This is the correct answer although more may be controlled than just ignition timing (the dual independent camshaft timing and fuel delivery may be altered as well, not sure for the 5.0L). All the 'you have to burn 93' comments are incorrect. Will it run better on 93? Maybe, but on a hot day the differences may be the most noticeable if at all.

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[GoBlues38]

This is absolutely right.

Octane is actually a fuels resistance to burning. The higher the octane, the LESS it wants to burn (or ignite, more specifically). Most people don't understand this.

Most cars, timing is set and doesn't move. Use the lowest octane it will run. Usually manufacturers recommendation unless tuned. Which means higher octane is less power if timing doesn't change.

.

Finally people who actually know what they are talking about.

However, the mustang adds timing until knock is sensed. More octane yields more timing which yields more power. So higher octane means more power and more efficiency.

Except when you are not working the engine hard, there is no need for timing advance, hence no danger of pre detonation. Lower octane works fine for say highway cruising.

The problem is, its maybe 1 or 2 road trips a year where I run an entire tank (400+ miles) on a highway @ cruise speeds.

 

[Daytona Coupe]

This is actually NOT right.
Octane measures resistance to detonation - not burning. There is a major difference. Detonation is an instant explosion (knock) and you don't want that. A lower octane fuel will burn faster and is more likely to detonate. If you don't have detonation, then fast burning helps to make sure you are getting all of the energy out of the fuel - which is why low octane fuel CAN make more power. If you run more octane than you need, then the burn is slower and you may not be getting all of the available energy out of the fuel - but it is generally worth it to prevent the possibility of detonation.

 

[cush]

Yes it is.....trust me I was shocked. page 127
http://www.fordservicecontent.com/F...-Owners-Manual-version-1_om_EN-US_07_2014.pdf

Page 267 states 87 is the minimum octane rating, so take it from there... or not!

 

[Free Agent]

In 95% of driving situations you will see no effect of 87 over 93 octane. Its that 5% of driving situations where it makes a difference. And if you hit the track that 5% becomes 100%. If you want the security of knowing you will have the least amount of detonation if you go WOT then run 93. If you aren't worried run 87, but don't gripe and complain when stock for stock the 93 octane vehicle outperforms the 87 octane vehicle albeit even for 5-10 HP. As they weather gets warmer and IATs rise you are going to see more knock retard at all throttle conditions. Hotter air is thinner air and timing is going to be pulled although I have never seen the timing tables for the 5.0 I am and will go with 93 so I have the maximum potential on all days and all situations. If that isn't a priority, go with 87. End of story frankly.

 

[cush]

In 95% of driving situations you will see no effect of 87 over 93 octane. Its that 5% of driving situations where it makes a difference. And if you hit the track that 5% becomes 100%. If you want the security of knowing you will have the least amount of detonation if you go WOT then run 93. If you aren't worried run 87, but don't gripe and complain when stock for stock the 93 octane vehicle outperforms the 87 octane vehicle albeit even for 5-10 HP. As they weather gets warmer and IATs rise you are going to see more knock retard at all throttle conditions. Hotter air is thinner air and timing is going to be pulled although I have never seen the timing tables for the 5.0 I am and will go with 93 so I have the maximum potential on all days and all situations. If that isn't a priority, go with 87. End of story frankly.

I can't place the quote, but I've read that Ford claims only a 1% reduction in power when using 87 octane fuel, which means to me the 435 HP was developed using premium 93 octane fuel....

 

[drbrian722]

The 435/400 numbers are achieved with 93 octane and the recommended fuel is Premium Unleaded.

It is completely safe to run 87, but the computer will dial it back and you will not be able to achieve those power numbers. The drop is between 1-3% so it's not a huge difference.

 

[ero 5.0]

So nobody offers 93/94 octane fuel in my town, but there is a 76 station that has 100 octane. So my question is: Is it the same as filling 15 gallons of 93 is I were to fill say 10 gallons of 91 and then 4 or 5 gallons of 100? Or does it not work like that to mix diff octanes? Thanks.

Ok thanks to all who jacked my thread, but does anyone have an answer my question in the first post? Thanks.

 

[drbrian722]

Ok thanks to all who jacked my thread, but does anyone have an answer my question in the first post? Thanks.

I knew I was forgetting something!
Yes, mixing octanes averages them by volume.

Use this link
http://www.wallaceracing.com/octane-mix-calc.php

 

[ero 5.0]

I knew I was forgetting something!
Yes, mixing octanes averages them by volume.

Use this link
http://www.wallaceracing.com/octane-mix-calc.php

TYVM! I wasnt sure if there was an issue with mixing diff octane. Thanks again.

 

[SVTFreak]

This is actually NOT right.

Octane measures resistance to detonation - not burning. There is a major difference. Detonation is an instant explosion (knock) and you don't want that. A lower octane fuel will burn faster and is more likely to detonate. If you don't have detonation, then fast burning helps to make sure you are getting all of the energy out of the fuel - which is why low octane fuel CAN make more power. If you run more octane than you need, then the burn is slower and you may not be getting all of the available energy out of the fuel - but it is generally worth it to prevent the possibility of detonation.

This is technically correct but most people do not know (or understand) the difference between resistance to detonation, ignition, or burning. Either way you describe it, my post is still correct.

As far as what's better? Do you want the few extra ponies or the cheaper gas bill? 93 really isn't and safer since timing is advanced to meet the new octane. If timing was set, you would be sacrificing power for safety but it's dynamic. Imagine if you was a foot from a ledge. If someone moved the ledge, you would be safer. But in the 5.0, the computer moves you to a foot from the ledge again even when it moves.

 

[AngryBeavers]

Why not just put in the better fuel and know you're getting the best quality? The difference from 87-93 octane is at most 50 cents. On a 12 gallon fill up thats like a difference of 6 dollars and you'll get advertised performance and mpgs. Its a performance car put the extra effort in to keep it that way

 

[Free Agent]

I can't place the quote, but I've read that Ford claims only a 1% reduction in power when using 87 octane fuel, which means to me the 435 HP was developed using premium 93 octane fuel....

Yes that was what I was trying to get across.

 

[Free Agent]

Why not just put in the better fuel and know you're getting the best quality? The difference from 87-93 octane is at most 50 cents. On a 12 gallon fill up thats like a difference of 6 dollars and you'll get advertised performance and mpgs. Its a performance car put the extra effort in to keep it that way

Increase in octane isn't necessarily an increase in "quality". Often times it is especially if you frequent top tier gasoline retailers. But I'm right there with you at a 30 cent a gallon difference in my area, $150 bucks a year extra is money well spent for the full horsepower of my engine.

 

[Free Agent]

This is technically correct but most people do not know (or understand) the difference between resistance to detonation, ignition, or burning. Either way you describe it, my post is still correct.

As far as what's better? Do you want the few extra ponies or the cheaper gas bill? 93 really isn't and safer since timing is advanced to meet the new octane. If timing was set, you would be sacrificing power for safety but it's dynamic. Imagine if you was a foot from a ledge. If someone moved the ledge, you would be safer. But in the 5.0, the computer moves you to a foot from the ledge again even when it moves.

Correct but in equal vehicles in equal conditions, two cars one with 87 and the other with 93, the 93 is going to be able to sustain or advance timing and ensure greater power/torque numbers and "beat" the car running 87. 87 is never going to give you the full potential like 93 can. Where that point of diminishing returns with octane is on this engine I don't know although someone who has access to the timing tables and data logging could probably figure it out. You are "safe" with both, 93 will outperform 87 in aggressive driving. Choose the one that suits your needs.

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