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5.0L V8 Technical Discussions Any questions about the 'Coyote' engine, transmission, exhaust, tuners/CAI, or gearing can be asked here!

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Old 05-09-2014, 08:27 PM   #31
jz78817
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Quote:
It costs more because it has extra refining steps.
no, not really. octane rating of gasoline is about the additive package. the base fuel is the same. a fuel's octane rating is an indicator of its ability to resist autoignition, meaning how much heat and pressure it can undergo without lighting off until the spark plug fires. additives drastically alter the base gasoline's anti-knock properties; one of the reasons tetraethyl lead used to be a popular additive to gas was because even a tiny amoung boosted the fuel's octane rating substantially. Of course, it had the nasty property of fouling the air we all breathe with lead...

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I'm pretty certain that it doesn't burn hotter/cooler, it just determines if it is resistant to knock/detonation
this is accurate. the burn rate/temperature of gasoline is pretty much consistent across all grades.
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Old 05-10-2014, 04:46 PM   #32
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additives for anti-detonation - low octane with spark advance on a high compression engine means the fuel will ignite / detonate sooner than it should causing pinging or blasting holes in your pistons is how I understand it. Old school aircraft engines like a PW R2800 (2800 cubc inches with 18 cylinders) were built for 150 octane av gas (if I remember correctly) which has not been made for 40 / 50 years. At high power settings they also used ADI (anti detonation injection) fluid (water / methonal) as well to control detonation. These engines are now stuck with 100/ 130 octane and can no longer pull full rated power.
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Old 05-11-2014, 12:00 PM   #33
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You can't compare avgas and mogas ratings. They are rated using different methods and have completely different purposes in rating. Avgas typically has two ratings. The low one is "aviation lean" which is your cruise performance and "aviation rich", which produces max power on the same fuel.

The PW2800 was quite capable of making 2800 horses, rated, in later versions, on 115 octane fuel (actually 115/145). The best at this were the Chermans. High octane avgas got more scarce as the war went on and they really had to figure out how to make rated power on what was, essentially, 87 octane fuel. People don't run these old birds as hard today because the engines are 70 years old, parts are hard to get and $$$$ and there's little available 100/130 or 115/145 (leaded) avgas any more. Nowadays, 100LL is the highest performance leaded avgas commonly available and it hasn't got enough lead to keep these old engines happy in stock form.

Main differences with avgas over mogas is the much higher vapour lock resistance. Vapour lock is easy to get at altitude and that's it, engine shut down and probable crash landing so, pretty serious stuff.
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Old 05-13-2014, 03:38 PM   #34
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My manual specifically recommends high octane.
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Old 06-29-2014, 09:49 AM   #35
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When I bought my car, I went with the salesperson so that he could give me a full tank of fuel. I asked if he was going to use 93 octane or 87. He told me if he pumped 93 octane, and turned in that invoice, he would be either reprimanded or fired by his boss. This is coming from a Ford dealer on a new 2014 Mustang GT. I typically mix my gas at half tank. Once using 87 and next time 93 octane. I have tried running both separately, and I felt no difference between them at all, even at low rpms.
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Old 06-29-2014, 06:07 PM   #36
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Originally Posted by PeteInFlorida View Post
When I bought my car, I went with the salesperson so that he could give me a full tank of fuel. I asked if he was going to use 93 octane or 87. He told me if he pumped 93 octane, and turned in that invoice, he would be either reprimanded or fired by his boss. This is coming from a Ford dealer on a new 2014 Mustang GT. I typically mix my gas at half tank. Once using 87 and next time 93 octane. I have tried running both separately, and I felt no difference between them at all, even at low rpms.
93 octane on the stock Ford tune is useless. The PCM's ECU is programmed at most to exploit 91 octane and nothing more. The PCM does not store any timing advance values for anything above 91 octane.
The reason being is 93 octane is not available in most places with 91octane being the best fuel you can buy at the pump.

But since you mix 87 octane and 93 octane half and half, you are hitting around 89-90 octane in the end. So you are close to the max PCM tuning programming, assuming you are still using the stock Ford tune.

To be very honest, you will not feel the difference between 87octane and 91octane on the stock tune. The most crank torque you will get is 390 ft-lbf, with maybe only 385 ft-lbf on 87 octane. 5 ft-lbf crank torque gain is a very small, it is more like 3ft-lbf gain at the wheels.
The only way you will feel more power is if you get an aftermarket tune.
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Old 07-10-2014, 12:20 PM   #37
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I run 87 in my 2014 5.0 most of the time. Because, most of the time I am just commuting back and forth to work and honestly wouldn't miss 50 hp! Even with 87 octane, the car is stupid fast for a 100% stock-off-the-shelf Mustang.
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Old 07-12-2014, 10:45 AM   #38
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Quote:
Originally Posted by PeteInFlorida View Post
When I bought my car, I went with the salesperson so that he could give me a full tank of fuel. I asked if he was going to use 93 octane or 87. He told me if he pumped 93 octane, and turned in that invoice, he would be either reprimanded or fired by his boss. This is coming from a Ford dealer on a new 2014 Mustang GT. I typically mix my gas at half tank. Once using 87 and next time 93 octane. I have tried running both separately, and I felt no difference between them at all, even at low rpms.
Same here. I asked for 91, and my salesman said he was only authorized to do that for Shelby's and one other vehicle that wasn't mine.

I fill up early, alternating between 89 and 93, as 91 is often unavailable as pumps will be 87, 89, then jump to 93. Some have 91.

Last edited by GTC; 07-12-2014 at 10:48 AM. Reason: I typically alternate
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Old 07-13-2014, 10:39 AM   #39
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My local Shells do 93 octane for the price of 89 on Tuesdays... not sure if that's just a regional thing, but that's the only day I fill up.
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Old 07-13-2014, 01:07 PM   #40
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My local Shells do 93 octane for the price of 89 on Tuesdays... not sure if that's just a regional thing, but that's the only day I fill up.
I have never heard of this before - you must have incredible luck.
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Old 07-13-2014, 01:07 PM
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