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Discussion Starter · #1 ·
So, I assume we all know that the Croc wants 93 but here in CA we only get 91, even at sea level.

I saw an E85 pump the other day and blended a little into my truck for poops and giggles and thought...hm, this is a whole lot cheaper than putting 4 gallons of 100 octane at 8 bucks a gallon into my tank to get it up to 93.

Can the Croc handle 4 gallons of e85 per tankful?
 

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So, I assume we all know that the Croc wants 93 but here in CA we only get 91, even at sea level.

I saw an E85 pump the other day and blended a little into my truck for poops and giggles and thought...hm, this is a whole lot cheaper than putting 4 gallons of 100 octane at 8 bucks a gallon into my tank to get it up to 93.

Can the Croc handle 4 gallons of e85 per tankful?
Sure, if you don't care about your warranty. Porsche will void your warranty if it finds out you've been using more than 10% ethanol in your tank.
 

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So, I assume we all know that the Croc wants 93 but here in CA we only get 91, even at sea level.

I saw an E85 pump the other day and blended a little into my truck for poops and giggles and thought...hm, this is a whole lot cheaper than putting 4 gallons of 100 octane at 8 bucks a gallon into my tank to get it up to 93.

Can the Croc handle 4 gallons of e85 per tankful?
Ethanol makes less power than gasoline, so you'd be better off just using 91 non-Ethanol if you don't want to mix in a little race fuel. Ethanol is also very hard on your fuel system.
 

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Discussion Starter · #4 ·
Ethanol makes less power than gasoline, so you'd be better off just using 91 non-Ethanol if you don't want to mix in a little race fuel. Ethanol is also very hard on your fuel system.
That just means fuel economy will be slightly lower. E85 has an effective octane of 105.

I'm of course concerned about the warranty issue, but is there any way they would know? This goes back to the question, would a tank of 25% E85 (that means ~21% ethanol) damage the system?
 

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That just means fuel economy will be slightly lower. E85 has an effective octane of 105.

I'm of course concerned about the warranty issue, but is there any way they would know? This goes back to the question, would a tank of 25% E85 (that means ~21% ethanol) damage the system?
There's been some discussion about this before, in other threads. The consensus was that the engine itself would probably be OK, but the hoses and seals are not specifically made to handle exposure to higher concentrations of ethanol (which is a corrosive), and as such would have a higher likelihood of premature failure.

Even if Porsche were not able to catch someone using the wrong fuel, are you the kind of person who's willing to commit fraud just to get a free warranty repair for a problem that you potentially were responsible for?

The bottom line is that these engines have not been sufficiently tested with E85 or any fuels with more than 10% ethanol. Why take the chance just to increase your octane when your engine can handle 91 octane fuel just fine?
 

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That just means fuel economy will be slightly lower.
No, it also means your engine will make less horsepower (and I assume your reason for wanting higher octane was to make more horsepower). Octane is not synonymous with power. It only means its resistance to detonation is greater. Higher octane is actually less volatile than lower octane fuel. The only time that E85 is a horsepower benefit is with a turbocharged car that can have its boost set higher than stock. With a normally aspirated engine, the more Ethanol percentage, the less power it will make.
 

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I saw an E85 pump the other day and blended a little into my truck for poops and giggles.
You might get more poops and giggles than you bargained for. Ethanol corrodes metal, eats plastic fittings and rots rubber hoses. Ducati has already replaced hundreds of motorcycle fuel tanks (while not admitting that they have a problem) because of ethanol. BMW motorcycles are beginning to show up with ruined injectors. The problem has been traced to ethanol. Check out any number of BMW car forums and you will see quite a few posters complaining about ethanol. And in just about all of these reports we are talking about 10% ethanol . . . not the E85 variety which is 15% ethanol.

Do you have any friends who are recreational pilots? Ask them how they feel about ethanol in their aviation fuel? They don't want their engines "pooping out" at altitude. :eek:

But it's your car. Run ethanol if you want to. :cheers:
 

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Discussion Starter · #9 ·
No, it also means your engine will make less horsepower (and I assume your reason for wanting higher octane was to make more horsepower). Octane is not synonymous with power. It only means its resistance to detonation is greater. Higher octane is actually less volatile than lower octane fuel. The only time that E85 is a horsepower benefit is with a turbocharged car that can have its boost set higher than stock. With a normally aspirated engine, the more Ethanol percentage, the less power it will make.
You're incorrect. Less volatility (through higher octane, be it in gas or ethanol) means the motor can advance the spark, which means more power. Running 91, the motor retards the spark which reduces power. Ferrari ran E85 in their cars specifically for the octane.

That being said....

E85 - Wikipedia, the free encyclopedia

E85 has an octane rating higher than that of regular gasoline's typical rating of 87, or premium gasoline's 91-93. This allows it to be used in higher compression engines which tend to produce more power per unit of displacement than their gasoline counterparts. The Renewable Fuels Foundation states in its Changes in Gasoline IV manual, "There is no requirement to post octane on an E85 dispenser. If a retailer chooses to post octane, they should be aware that the often cited 105 octane is incorrect. This number was derived by using ethanol’s blending octane value in gasoline. This is not the proper way to calculate the octane of E85. Ethanol’s true octane value should be used to calculate E85’s octane value. This results in an octane range of 94-96 (R+M)/2. These calculations have been confirmed by actual octane engine tests." [12]

So it's really much lower octane than displayed on the pump, so this all is pointless. :hilarious:
 

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You're incorrect. Less volatility (through higher octane, be it in gas or ethanol) means the motor can advance the spark, which means more power. Running 91, the motor retards the spark which reduces power.
I'm well aware of that, but you're not taking into account the fact that Ethanol produces less energy (Horsepower) when being burned compared to gasoline. This effect makes the small increase in octane negligible (and harms the fuel system). Using 93 octane gasoline will produce more power than running 110 octane Ethanol in your Cayman. If you want to bump your octane from 91 to 93 (beyond which there is no benefit in a Cayman), mix in a little race fuel, not E85. Even then, you'll likely feel no difference.
 

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I do that frequently, and there is a very noticable difference :) At 7-10 bucks a gallon though, it gets expensive.
Interesting that it's so noticable. I live in Denver where there is no real difference in power between 91 and 93 octane, since the thin air reduces the compression (so 91 is plenty of octane not to alter the timing- no risk of detonation).
 

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Discussion Starter · #13 ·
Interesting that it's so noticable. I live in Denver where there is no real difference in power between 91 and 93 octane, since the thin air reduces the compression (so 91 is plenty of octane not to alter the timing- no risk of detonation).
Ya, I don't fully understand it but octane works differently at altitude. The pumps in Utah were 86 / 88 / 91 IIRC, but I'm pretty sure it had to be the same gas. I live at 1200ft.
 

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You might get more poops and giggles than you bargained for. Ethanol corrodes metal, eats plastic fittings and rots rubber hoses. Ducati has already replaced hundreds of motorcycle fuel tanks (while not admitting that they have a problem) because of ethanol. BMW motorcycles are beginning to show up with ruined injectors. The problem has been traced to ethanol. Check out any number of BMW car forums and you will see quite a few posters complaining about ethanol. And in just about all of these reports we are talking about 10% ethanol . . . not the E85 variety which is 15% ethanol.

Do you have any friends who are recreational pilots? Ask them how they feel about ethanol in their aviation fuel? They don't want their engines "pooping out" at altitude. :eek:

But it's your car. Run ethanol if you want to. :cheers:
Since ethanol (and alcohols in general) have a tendency to pick up water (hygroscopic) and undergo hydrolysis, it may be the acid by-products which are corrosive. Plus any significant water contamination will reduce octane rating by 3-4 points. Hence, a local mechanics recommendation to add Stabil (marine) once in a while, use "high test" gasoline in lawn mowers and snow blowers, and not store gasoline for home use long term.
 

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I heard people talkin' about runnin' their vehicles with 85% alcohol, so I thought I'd give it a try. I started usin' 190 proof Everclear, since it has a higher alochol content than the 85% stuff other people use. I figured that would make it go faster. Now my vehicle just swerves everywhere. It sure makes for an interesting drivin' experience.
 
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