Lets talk Octane..... What is the consensus on grade of fuel? I'm running 96 x 71 bore & stroke with .060" deck height 58.8cc chambers in the heads, and flat top pistons with no valve reliefs, and figure my CR is around 8.6:1. I'm thinking I can run regular, but no idea.

I've been running Chevron 92 so far, but dont want to wast $ and leave unburnt fuel residue. The higher the octane, the more resistant the fuel is to combustion, so unnecessary use of 'hitest' is dirtier combustion wise than regular.

I haven't done any experimenting yet, but wanted to get some experience before I do. I plan to run the current tank down to close to empty, then put in 5 gallons of regular and see how that goes, but just wondering.

With that compression you should be able to run reg.

Altitude also matters.
The higher the alt. the lower octane you can run with a given setup.

I am closer to 10:1 and I run 92 at 1 mile high.
I run the same gas in my BRZ which is 12.5:1 but has knock sensing tech with timing compensation.

Steve -

My 88 Westy WBX-4 with Digifont is a development of our 914 engines & at about 8.6:1 IIRC & factory specs it at 87 (85-87), & it's run fine since 88 at all altitudes & long XC trips for 28 years.

Also, I always ran 87/85-87 in my `73 914-2.0 with D-jet & stock CA/USA CR (7.6:1) & know folks with the Euro P&C at 8:1 who also used regular with no problems.

So I think you'd be okay, as the others above have said.

Cheers!
Tom
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Great, thanks guys. Now I just need to find the co-ops that sell non ethanol fuel.

I think the better thing to consider is that ethanol fuel sucks. I am lucky that a gas station near to me sells straight 92 octane gas. I use it in all my lawn equipment and two stroke motors. The gas doesn't go bad in 30 days and destroy all the carbs and fuel lines. The extra cost is worth it in no repairs.
Brian

My '74 2.0 L with dual Dellorto carbs loves 90 Octane Non-Ethanol. The difference between using it and the ethanol crap is like night and day. I have had tankfulls of ethanol blends that caused the car to run so poorly I was forced to siphon it out. Put non-ethanol back in and everything was back to normal.

Ansbacher

Octane is a rating referring to the tendency to detonate. So the rating refers to a ratio of mix of octane and heptane. That is the standard. Octane and heptane are two different carbon chain molecules fuels. Buying a higher rated octane fuel doesn't mean it is a dirtier fuel.

I think when you posted combustion you meant detonation?

The propensity for detonation is caused by many factors but mostly by the combustion chamber and how the engine breathes and the fuel, so several things besides that octane rating.

Jake Raby has wrote untold threads on this.....he mostly says this in a few words as "its all in the combo" on how to create optimum power, not just in the CR ratio or the octane rating of the fuel.

Speaking of Ethanol; manufactures of AFR gauges and sensors warn against fuel with additives or contaminants; the sensors self destruct in their presence.

Any thoughts whether the ethanol could affect AFR sensors ?

Yes, brain fart, detonation. Due to its 'resistance' to detonation, it burns slower and sometimes not as completely, hence 'dirtier'

Jake said something in a few words? Bur he is spot on with that comment, hence all the relevant data in my original post.

E-Free!

http://www.pure-gas.org/

You sir are a god......

Anything above stock CR you likely should move up to premo, but seeing the age of our cars I use pure gas and so that is premo here by default.



I do have a hard time believing that ethanol would harm a Bosch O2 sensor, they're in millions of modern cars. They must be talking about "fuel treatments."

I know that dragsters running on methanol the AFR readings double.
So it stands to reason that ethanol is affecting the readings, but by how much I don't know, I would imagine not a whole lot.

Ethanol-free... Only a dream here in Maryland. Oh how I wish

The one thing I've wondered about is if you remove the ethanol from the gas what would the octane rating be on the end result?

It's easy to remove, just add a bit of water and it will separate the ethanol from the gas.

If you're running a stock mild, mild, mild cam I would suggest sticking with premium. Porsche specified 87 octane for the US-spec 2.0 with 7.6:1 compression, and the equivalent of 91-92 octane for the Euro-spec 2.0 with 8.0:1 compression. They do try to err on the conservative side, so you can probably run higher compression on ~92 by just giving up some of the safety margin.

If you have an aggressive cam, you will effectively "leak out" some of the compression. How much depends on more factors than I can calculate--it's usually best to talk to the people who designed your cam grind to find out what they think you should run.

--DD

I run cheap gas in everything I own.
Audi, 914s, 911, truck, everything

I don't see the point of premium if the car is tuned properly, just a good tune up.

Ethanol has reduced the power by 15% already.

Wow....great question.

Any Petrochem Engineers out there?

Ethanol is basicly a octane booster, so I would think it would go down. What I'd like to know is if you were to remove the ethanol from 91 will you get at least 87 octane?

Just FYI. Pure-gas.org lists 42 ethanol free stations in Maryland. Might not be near you, but you might want to check it out.

Well, I'm a chemical engineer, but I haven't worked in the petroleum field since college. Still, I don't think it would be wise to put water into an ethanol-gasoline blend. Ethanol and water are soluble in each other, so the ethanol-fuel mixture would simply dissolve the water until it couldn't anymore, at which point phase separation would occur. But the mixture of ethanol-fuel will hold the water (in this case, the fuel mixture would be the solvent, water would be the solute). One might have some success by using a vast quantity of water and pouring some ethanol-fuel into it, gently mixing it to get the ethanol and water to mix, then letting the mixture re-separate, but I don't think that would work very well - it would be a competing dissolution process and I don't know the equilibrium constants for ethanol in water vs. ethanol in gasoline. Better separation technologies would be needed such as fractional distillation, solvent-extraction with a better solvent than water (I think), possibly using a resin bed of some kind as a catalyst for separation.

EDIT: see here... http://www3.epa.gov/otaq/regs/fuels/rfg/waterphs.pdf

Is it usually only the 91 octane that comes as ethanol free? From what I am seeing on the pure-gas.org site so far they are all listing 91 octane in the 'details' section.

Brett

There ya go Mark.....like making Crack or Meth....I love this place.

Now I know why I am a Civil Eng.......hated chemistry.

I'm no chemist (and I don't play one on TV) but...one of the tests I do as an SCCA scrutineer is to determine the amount of ethanol in the fuel (we allow 10% max).

The method I use is to take a sample of fuel from the car and pour it into a 100mL graduated cylinder to the 90mL mark. I then pour in 10mL of water. Shake it up briskly and then let it sit. The water will "capture" (whatever the correct word is) the ethanol from the gasoline and a clear line will emerge between the gasoline and the water/ethanol mix. The difference between the measurement of the mix and my original 10mL of water is how much alcohol was in the fuel; simple math (difference divided by 90) tells me what the percentage was.

If this is something you wanted to do yourself, you can, but it presents a couple problems to you:

One, the water/ethanol mix goes to the bottom, but how are you going to decant the gasoline off the top efficiently and at the production levels you're looking for? And what are you going to do with the resulting dregs (please don't pour it down the drain!)

Two, as noted above, ethanol increases octane (which is why SCCA limits max level). If you decant out all the ethanol, you have no way of knowing what the resulting octane of your gasoline is. And it's not a linear add/subtract ratio (i.e., you can't add 50/50 94 octane and 110 octane together and call it 102; it comes out to more like 98).

You're far better off finding a local supplier of non-ethanol fuel. Easier, cheaper, less mess and hassles.

GA

our ethanol-free "marine gas" sold here is 87 octane so that is what i put in the 914. today its $2.15, same price as premium 93 octane at the same station. Our regular gas just today hit $1.59 btw

That's why I never tried it, in my area 91 premo is pure gas.

Thank's for the info Madswede, I just brought this up because there's a couple guy's doing this on youtube.
I know nothing on the chemistry end other than how to do the simple test for ethanol.

Yeah OK, I sit corrected! I was mistaken in my conclusion, obviously since it works, and yet I had all the evidence on why! What I mean is, the more I think about it, as long as water and ethanol are infinitely soluble in each other and have limited (or in water's case, no) solubility in gasoline, then it stands to reason that EtOH-water would dissolve in each other then separate from the gasoline ... clearly the solubility of EtOH in water must be higher than in gasoline! In fact, that is exactly what solvent-solvent extraction is, which is one of the things I suggested. Hey ho, I'm rusty in that area. Thanks for the correction!

What you went on to say makes a lot of sense to me ... as you concluded it seems very hard to separate the water by decanting (maybe a large container with a valve at the bottom would work if some gasoline was sacrificed, but there sure are easier ways, like just buying EtOH-free gas. I like your point about the octane rating too. Makes sense to me.