Which would you pick and why. I have my idea but want to hear yours first.

Obviously, more energy (BTUs) in gas but more advance can be had with higher octane. Does that really get you anything with EFI setups?

Someone pointed me recently to evidence that E10 is only 2% less energy-filled than pure gasoline. Never went back and looked hard. (But I'd thought it was closer to 5% less.)

My AFR heads are much more efficient than stock heads. Could the answer depend on head efficiency? Or, usage?



(FWIW: I live halfway between these two types of (BP) fuel options. 100% gasoline option is about 12 cents more per gallon.)

 

Use the gasoline that your car runs best on & makes you happy too.
retuning for E10 gas is a good thing.

 

All the fuel lines injectors and tune up was done for real gasoline so pick for there maybe.
Dave

 

Well it it's 2% you give up 6chp; if 5% you lose 15chp...is that worth the $0.12/gal??

I own/drive my Vette for the performance as well as style, so I'd get the 100% gasoline if possible...

 

Greg it depends on if your power is being limited by knock retard at wot or not. If you can acheive max HP without knock retard on 91 octane then use it. If you have to limit ignition advance on 91 octane but not 93 octane E10 then use the 93 octane fuel since it will prlvide more power in that situation.

 

E10 does not loss HP or TQ over 100% gasoline, it requires approx 3% more fuel to run at stoichiometric. The power difference is negligible if everything else is the same.

 

This is the thing I've had trouble deciding on. Whether 2 or 3%, there's obviously a difference in E10 vs gas. There's more BTUs in a molecule of gas, BUT if you use more E10, do they really end up the same?

My (383) is tuned with a 14.3 stoich. (With a primer from Bjankuski BTW....Thanks Brian!) OTOH, I was under the impression that the stoich figure was only a guide for the ECM to get started. In closed loop, I assume it adjusts whether set for 14.3 or 14.7. IOW, that the result is the same (except for open-loop warm-up and WOT).

If it's really the case that 3% more E10 provides the same (BTUs) power as gasoline, then I should stick with the E10 I dyno-tuned my car on. If there was more power in gasoline....3% increase would provide about 13ft/lbs of torque on my setup.

Compared to a stocker, that's about the equivalent of doing 1.6 roller rockers. That's why I considered it worth debating.

 

The long and short is (if you really want to get picky is) E10 actually makes slightly more power then straight gasoline. Ethonal has less power per gallon of fuel but the amount of fuel needed to run at WOT has more BTU's in it so more power is produced, but you use more fuel.

 

Data log it and see if you get any timing retard with the 91. If not, run the 91 for max power. I try to avoid ethanol as much as possible.

 

There is no comparison to 100% gasoline. I found some in New Mexico and I was getting an extra 4 MPG. All went back to normal the moment I got back to 90%/10% gasoline.

Its a money thing, less MPG, more gas you need to buy and nothing to do with the environment.

 

If E10 requires 3% more fuel than gasoline, 3% times $4/gal means 12 cents difference.

If (and since) E10 is 12 cents cheaper, then fuel costs would be the same.

Power would be the only other deciding factor. (I'm a bit surprised that, by adding the 3% additional E10, you'd end up with a higher power output. OTOH, Brian is the only one I know of running an E85 setup (IN THIS THREAD)!

OTOH, I would give some consideration to emissions -- as I'm one of those people who put cats on my performance motor.

I don't really know the percentage difference between emissions of one vs the other and I doubt anyone here does either. So, I have to acknowledge PLRX in the sense that emissions (esp for one car) is out of this debate.

Of the last three posters, I consider all very knowledgeable. OTOH, they don't seem to agree. I guess this is a subject we aren't very versed on.

Even if I decide to try the MPG test, I've no idea if I would need to retune for a fair test. I could data log and reset any necessary timing cells. OTOH, for a MPG test, I'm doubtful that I'd pull timing on either fuel for a "cruise" test. More importantly, would resetting the stoic from 14.3 to 14.7 have any effect? If/since the O2 sensor really has the "final say", you'd have to think no. You'd also have to think time would be necessary for fuel trims to recalibrate -- with any switch in fuel.

 

Greg, you are correct that the O2 sensor has the final say and as far as E10 is concerned as I mentioned in my prevoius posts it would be very hard to detect any real changes in power or gas mileage as long as no knock was detected.

 

The potential thermal units are similar, the potential power and all that.. BUT the correct fuel/air ratio is different.

Gasoline is 14.7:1

E-85 can be around 14.1:1

This makes a difference in the advance and most important of all, what the basic engine COMPRESSION RATIO can be in order to maintain the correct a/f ratio or stoichiometric ratio.

the lower the stoichiometric ratio the lower the compression has to be to be efficient otherwise the ratio is incorrect, the fuel is lean or rich and the combustion process is corrupted.

Remember the 70s when the compression ratios all dropped from 10:1 to 8:1 ?
That was to corrospond with the falling octane ratings of the time,. when 100 oct was called "ethyl" and regular was in the 90s. Federal guidelines lowered the oct in steps...and now 93 is no longer available is some states and 91 is going away soon.

To burn high alcohol blends that are rated at 91 oct....fine, as long as you drop the compression ratio in the engine so the stoichiometric ratio is correct. Thats why E-85 don;t work well for engines with more than 8.5:1 compression. Too much air so its lean...and runs like crap because its not getting sufficient fuel for the air in the combustion.

 

You should have posted back in 2007, so we could tell "frenchy"....
http://forums.corvetteforum.com/c4-t...i-concept.html


BTW...E10 is 14.1,,,not E85.

Regarding compression, since when do you have to lower it to maintain a given stoich? If we could get current fuels to avoid pinging at 13 or 14:1 compression ratios, engines would still run AND make more power. I thought detonation was the real issue.

FWIW, I have never tried...though I should. I should log (scan) what my setup will do with lower octane fuels. Based on the way it ran with 91-E10 once, I have the feeling I could go to 89 w/o pinging. Good heads with good quench and inverted domes go a long way.

 

I tried mine on 89 once and it would have been fine for cruising. I data logged it though and at WOT on a balmy evening I got just a hair of knock retard so I decided to just run 93. If I was to take a long road trip and I knew I wasn't gonna beat on it I would consider 89

 

Exactly !

when you have 13:1 compression ratio that you MUST have a given amount of octane (guessing that 106min gasoline OR some near straight enthanol) for that much air being compressed. ..and then there is the issue of the appropiate ign timing advance. WHole other can of worms.

OR the flip to this is less octane or energy units mean there has to be a reduction/adjustment in the air thats compressed.

When a HIGH oct is available then it can use more air and maintain that proper sto-ratio.
When that fuel is reduced so is the sto-ratio and that means the amount of air (compression) must also be reduced.
Pure alcohol has a very high energy rating but we're not going to ever see the good stuff unless we are on an INDY car team...or at the strip in the alcohol class running with the big dogs..They get good fuel. We get blended watered down crap that barely burns.
I wonder why that is? Pure alcohol burns clean as far as I know. You cannot even see the flame....but that can't be used as fuel for street cars? I wonder why? Oil company manipulation of the fuel business?

Engines that burn straight alcohol are as high as 19:1...but thats straight alcohol. The E85 and blends for gasloline and flex fuel engines are way lower because of the wide difference in the stoichiometric ratio of each fuel.
I recall seeing one fuel that had an ideal CR of around 6:1... .while straight alcohol is 3 times that. Gasoline somewhere inbetween.

In the measured amount of fuel used in an engine with a given CR, the amount of fuel used might be doubled to match the CR. But since we're talking mpg and emissions as the goal of these blended fuels, the factory offers the flex fuel engines that just manipulate the amount of fuel for each type since the CR cannot be radically altered in a working engine. The CR is managed to some degree with variable cam timing...where the intake open time is reduced to regulate how much air comes in for certain fuels.

Regarding the "cruise fuels"...

When I am taking a hi-way trip or a long cruise and mostly freeway speeds...I'll use 89 or even 87 if temps permit and have no issues at all. It cruises fine. If I'm doing more city driving or "playing" around then it has to be 91+ or the engine tends to knock like a Jehovas witness...10.5:1 compression so it needs the octane to run right.

Ambient temps also dictate my fuel purchases....If fuel this summer stays much over $4 per gal and I NEED 91+ that may not always be possible. Going to be like Forrest Gump was under the hood...mildly retarded.
Already cost me $5 to drive the Vette to the store for a $2 loaf of bread !

I have learned thru experiments with these summer/winter blends that cheap low oct fuel means retarding the base timing several degrees. Good fuels mean going back to the full available advance because the fuel "handles" the timing by providing a long burn that does not knock so easily. I can;t run 89 and stand on the pedal....not when its fully warmed. It would blow a piston if I did that. BTDT.

Ita a balancing act. Octane rating, ambient temps and driving conditions.

 

Lee...I like you man...but I make no sense your post above. I'm pretty sure E85 is run by people who want to run higher compression. Not lower compression.

Plus, the amount of air mixed with the fuel (or visa-versa) is independent of how much you compress it. That's obviously generalized. But, I just don't get your thoughts above.

 

The amount of disinformation in this post is astounding! When I am not typing on my cell phone I will try and pull this thread back from the abiss.

 

He is not that far off.
Has Methanol Alcohol & Nitro Methane on his mind.
Liquid dynamite.

 

WTF are you talking about? Stoic and CR have zero to do with each other. It is all about octane values and no more.