91+e85=93?

[Legend]

I posted this on the Ford forum 8 hours ago... no response yet. I know somebody would have commented here already. I'll ask the question here also though because it would apply to an LGT just as well and there are some good minds here. My new car is posted here, BTW.

 

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New '07 Shelby GT owner here. Car equipped with Whipple S197 SC, cams, exhaust and is running 91oct e-tune from Brenspeed. I also have a 93 octane e-tune but no access to 93 octane. I have E85 all around me and I tuned my daily driver to run on E85 exclusively the last 4 years. Absolutely love it.

 

Eventually I will convert the car to run on E85 and get a dyno tune, but in the meantime I'd like to at least run the 93 e-tune. I'd like to make a habit of splashing 2-3 gallons of E85 in with every tank of 91. The effective octane should be >93 and have some nice knock resistance. Of course fueling will be thrown off initially, but once fuel trims set up it should run just fine (right?) I would need to be careful the first time I fill up the tank this way in order to let those fuel trims set up and not go WOT leaving the gas station as I'd be running lean. But from then on as long as I don't reset the ecu I should be good to go.

 

I'm brand new to these cars so somebody set me straight, please, if I am on the wrong track so I don't grenade the thing. TIA.

[bnguyenbb6]

Wouldn't stoich afr be different?

[Legend]

Definitely, but ecu should learn to add fuel via fuel trims (right?)

 

Sent from my DROIDX using Tapatalk

[Th3Franz]

I'm not sure how the Ford ECU adjusts the fuel trims. For transients, like tip-in and cranking, your fueling will be off a bit. For closed loop, I'm sure it adds correction like we're used to.

 

 

Let's do some math shall we?

3 gallons of E85 (85% ethanol, 15% gas) 105 octane

15 gallons of E10, 91 octane gasoline (guessing the tank capacity of the Mustang here)

 

So you end up with 4.05 gallons of Ethanol and 13.95 gallons of 91 gasoline. I'm assuming that the gas in the E85 is 91, but the stoich for gas is the same regardless if it's 87 or 93.

 

So you're effective blend would be 22.5% ethanol. If your 91 octane is pure gas, you end up around 15% ethanol.

 

Let's compare stoichs:

Pure gas: 14.7

E10: 14.13

E15: 13.845

E22.5: 13.4175

 

Your cranking and tip-in fueling will be short 9.55% for E22.5. Effective octane is a hair above 94.

[Legend]

^^ Awesome thought process, sir, thanks! So it looks like instead of 3:15 ratio, I'd be a lot better off with 2:16 ratio. I didn't do the math but seems like that would be closer to E10, and obviously the car is built to handle E10. I guess I need to find out how much ethanol is in our 91, if any. I don't think there is any during the summer but believe our gas gets 10% ethanol in the winter.

[Legend]

I calculate adding 15% E85 to 91 octane is the magic number to get 91octane to 93 octane (results in 93.1 octane) For a 16-gallon tank, that means adding 2.4 gallons of E85 per fill up. The resulting stoich is 14.0, which is a 5.0% difference in stoich versus gas. I feel very confident in the ability of fuel trims to accomodate that 5% during WOT and cruise. Tip-in and cranking fuel might be 5% lean, however, depending on whether fuel trims adjust other fuel parameters if not. But even if not, I don't think 5% less cranking fuel would be an issue at all.. but going 5% lean at tip-in is the biggest issue I can see.

[Legend]

Still kinda continuing this thought here and on the mustang forum but not getting a ton of help from either place... surprised there isn't a little more interest in this idea as it seems that a lot of people without access to 93 could benefit from "making" it with 91 and E85.

 

My latest thoughts:

 

Alright, I've got an SCT programmer with a 91oct tune and 93oct tune for my mods. I calculate that by adding 2.25 gallons of E85 to each 91octane fill-up (16 gallon tank capacity), I will have a resulting fuel with 93.0 octane and 14.0 stoich. I calculate that for the stoich difference (14.7 vs. 14.0), 4.8% more fuel needs to be added to avoid running lean. Closed loop will take care of itself well enough without tuning intervention, but it looks like that if I have the ability to add 4.8% (or 5% if only whole numbers allowed) more fuel to open loop via the SCT programmer I will have achieved my goal... (can I add fuel to a tuner's map via the SCT??)

 

That goal, ultimately, is to be able to run my existing 93octane etune by "making" 93 octane by blending 91oct and E85 in the right ratio and still having fueling spot on. I'll get the benefit of the extra power from the 93octane tune itself, the security of ethanol knock resistance, and maybe a touch more power from having more ethanol in the tank. And fueling should be spot on. Thoughts appreciated.. and checking my calculations appreciated too!

[rockle3]

I think that people arent that interested because it is more trouble than its worth. If you have E85 around why woudn't you just run straight E85 also with making a mixture you introduce the possibility of not making consistent mixtures. I understand that you're just doing this as a temporary thing and it should hold out but in the long run I just think its more headaches.

[Legend]

^^ Thanks for your thoughts. Yeah you are right... probably not for most people. But for me making a single map change once and using 2 pumps at the gas station instead of 1 isn't a big deal. A decent trade off for ~3-5% more power and the safety that ethanol provides. Free hp is hard to come by.

 

I'd fully recommend LGT guys go all-in on the E85 conversion. For me with my new ride, I'm already around 500rwhp (added supercharger, cams, full exhaust) and don't know if converting to E85 would put me at more power than is wise to run on the stock block. Additionally, the full conversion to E85 requires some expense, namely injectors and fuel pump(s). I might go there eventually, but would like the no-cost middle ground in the meantime.

[Legend]

Interesting parameter in my SCT software... "ethanol percentage" huh... will see if I can log this..

 

http://beeez.com/shelby/ethanol.jpg

[Th3Franz]

GM has an ethanol % sensor, although they are flex fuel. Wouldn't surprise me if Ford does as well, just for helping dial in fuel trims from the get-go.

[Legend]

Alright I found a local dyno tuner who really seems to understand what the hell I am talking about and is on board with my ideas.

 

I should decide on an ethanol percentage for my custom tune. I won't go E85 because my stock block is already pushed to the limit, running 12psi (note that I am at altitude where Patm=12.1 rather than 14.7, so my 12psi really "feels" more like 9-10psi to the engine). With the thread title I chose here my goal was simply to bring our standard pump 91octane up to 93octane. But as long as I am going to the trouble and paying the money I am thinking that I should decide on a little more ethanol. That is, why barely get to 93 octane and only get a little of the beneficial effects of E85? So I put together a little spreadsheet with different possible fuel blends:

 

http://www.beeez.com/shelby/FuelBlends.jpg

 

All data looks self-explanatory.. the Per16Gallons column is the amount of gallons of E85 I'd add to the tank at fill up (based upon an empty tank). Right now I am thinking that either E20 or E25 is the way to go. In addition, since I am at/near stock block max already and will retain existing fuel system, I won't tune aggressively up top past 4500-5000rpms so the whp plot won't climb much past 5000rpms.

[05COLEGGT]

Your calculations are mostly sound but your forgetting one VERY important fact, well two. lol. E85 percentage at the pump is not an exact Gas to Ethanol percentage. sometimes you'll get true E85, sometimes it will be E80, 75 or in the case of winter blends closer to E70. This is why true flex fuel cars have content analyzers that constantly measure the amount of Ethanol in the fuel blend and automagically adjust the tune to suit.

Now take an ECU that does not have a content analyzer built in but has to solely rely on fuel trims to sort everything out. What happens if say you tune on a blend that is actually closer to E70 and run on that for a while. Then unbeknownst to you you fill up with a blend that's closer to true E85? A true flex fuel vehicle will adjust the tune once it senses the content level and the driver will never know the difference. An ECU that's not designed for E85 will only be able to use the O2 sensors to adjust the tune over time. What happens when you leave the gas station and decide to romp on it? There's a good chance you'll run lean and detonate, that is unless you have a really fast knock sensing system that saves your bacon.

 

A GM system analyzes the fuel before it goes into the engine, your ECU analyzes things after its already been combusted. Which do you think is safer?

 

Now I'm not saying your gonna blow up your engine, but simple math isn't going to save it. You need to have safeguards built in and all the necessary gauges to monitor things. Maybe think about getting a Zeitronix Ethanol Analyzer with Gauge to keep a tab on your true content level instead of a pen and paper?

[CasopoliS]

I would fill up some 5 gallon jugs of E85 at the tank and take it home and measure it the old fashioned way. Then, once you know the E85 true%, plug it into your little Excel calculator and have it tell you how many gallons to put into you tank. Then you have the hassle of mixing it with the 91 octane at the right time, getting it to the dyno, etc etc.

 

So yea, maybe more hassle than it is worth. But who knows.

[Legend]

Great points, 05Coleggt! First, the spreadsheet is just an estimate that is providing me a framework of thought. I don't expect the values to be dead on but rather approximations. Fuel tuning will be done via tune to get the correct lambda and won't simply be programmed in without testing.

 

As for variations in E85 (down to winter E70, etc), my experience tells me the real differences aren't that great. I ran E85 for 4 years on the LGT and checked LV's year-round and did a lot of WB02 logging the first year or two. I was actually amazed what little differences I observed between summer and winter fuel trims and observed AFR's. I think the seasonal variations, in real life, aren't as great as advertised. I agree, however, they should not be ignored. I think in my spreadsheet I should "average" the E85 content and just call it 80% ethanol rather than 85. That way the fueling error is much smaller in the winter.

 

 

Let me work this through, assuming I choose E25 as the way to go. If I get tuned for E85 and it is truly 85% ethanol but then my pumps drop to 70% in the winter, I will get less ethanol... let's assume a fairly large drop to a resulting fuel that is E21. At least I'd be running a bit rich, not lean.

 

But that is not the end of the story! In the winter our 91octane becomes 10% ethanol. So, even though in the winter I might get a little less contribution of ethanol from E85, I get significantly more from the 91octane. I think we are talking fairly small fueling errors that look to be working in opposite ways that might not make a damn bit of difference in actual measured AFR's.

 

So glad you guys are helping pointing out problems, etc... Please keep them coming. I can still be persuaded not to do this but i like it more all the time.

[05COLEGGT]

Back when I had my Turbo'd Tiburon running Ethanol I constantly monitored my ECU's short term fuel trims as a kind of gauge what the content was. If I saw them get too far out of whack I'd know it was time to switch over to the winter or summer blend maps. My suggestion would be to forget about the halfass half this and half that or a 1/4 this and a 1/4 that method and just go 100% E85. May cost you some new injectors and possibly a larger pump, but the lower headache value would more than off set the cost.

[Th3Franz]

You can get a $15 ethanol content tester (titration) off ebay. My buddy runs E85 in his STI and it's a real simple check when you fill up. The blending differences vary by geographic location. Here in Wisconsin, we see DRASTIC blend changes between summer and winter.

[Legend]

I've talked to 4 reputable tuners now also. 3 Ford and 1 Subaru. They are split 2:2 on whether this is a good idea or not. The 2 that don't like it both say either run E85 or don't, but no blends. One is an etuner and I agree that it is a bad idea for etuning (without a WB02). Of the 2 that do like it, they aren't overly enthusiastic about it but agree it has benefits.

 

I'm still leaning towards doing it as follows:

 

1) Completely tune car on 91oct. This will be 1 of 2 maps on my programmer.

2) Go to gas station, put in 4.0 gallons of E85 and top off with 91oct. This first tank will be the exact 3:1 ratio of fuels 91:E85 (resulting in E21).

3) Retune fueling to reach correct stoich. Then, make slight tuning adjustments to take advantage of higher octane fueling and ethanol.

- Another more timing, as appropriate

- A bit leaner

4) Since I am not interested in peak power due to stock block already maxed out on 91oct and don't want to put a roll cage in for the strip, I will have no tuning adjustments made past 5000rpms.

 

That's it. In the future, when I fill up, I'll simply need to look at the gas gauge to determine how much E85 to put in prior to topping off with 91oct. If a half tank, I'd add 2 gallons E85. If a quarter tank, 3 gallons E85. If running on fumes, 3.9 gallons.

 

The fuel, if 85% ethanol in E85 will be 93.9 octane, and require 7% more WOT fuel.

The fuel, if 60% ethanol in E85 will be 93.1 octane, and require 5% more WOT fuel.

 

The difference in WOT fueling even if there becomes a wild swing in ethanol from E85 to E60 on the very next tank, is only a difference of 2%. In addition, when ethanol content goes does, it becomes a richer mixture, so safer if anything. I have no plans to test E85 content and realize that the fuel gauge might be slightly inaccurate. Neither error concerns me very much at all.

[Legend]

Here is what I would expect from this fuel and tuning... around 2-4% difference in wtq and 1-3% difference in whp with no appreciable difference in high-end power. Perhaps +20wtq and +10whp in the middle of the powerband. Doesn't sound like much but recall my other goal is safety, and despite the fact I introduce risk by blending fuels, relying on the fuel gauge, and accepting E85 differences, I still think running ~20% ethanol in the tank is better for the engine than running none.

 

(Plugged in numbers from previous owner's dyno sheet on 91oct, 1.13CF)

 

http://beeez.com/shelby/dynodiffe21.jpg

[CasopoliS]

umm.... I would stick with the 91 octane. I think you have enough power. Are you just bored, looking to tinker?

 

If your bored, take up another hobby! Your car is doing just fine

[05COLEGGT]

One question I have is how accurate is your fuel gauge? Even if it says close to empty how much reserve is sitting in your tank?

[Legend]

One question I have is how accurate is your fuel gauge? Even if it says close to empty how much reserve is sitting in your tank?

 

+1. I think THAT is the biggest concern. I keep hearing over and over again on this and the other forum that inconsistencies in E85 should be concerning me.. hell I wasn't concerned about that the last 4 years when I ran 100% E85 year round so I don't know why I would suddenly be concerned about running 1/5 as much E85 if I follow through with this plan.

 

But this is the real potential problem, I agree. Even if I fill up at exactly 1/4 tank every time and add 3.0 gallons E85 every time, how do I really know that there are 4.0 gallons remaining in the tank (indicating 1/4 tank)? The gas gauge goes above full and below empty, as it does in most cars.... so a single error of 0.1 or 0.2 gallons might not be a big deal, but over time those errors could add up. Hopefully they would cancel out (over 0.2 one time, under 0.2 the next time, etc.), but if all errors are in same direction fueling will become more and more off.

 

I've thought this through, however. My solution is to have a washout tank, once every 4-5 tanks. Flash to 91octane at the pump and run a whole tank through and start the E85 blend the next time when the 91oct is empty. This makes the whole scheme a little less attractive, however...

[05COLEGGT]

Bingo, bongo, boingo. When I first switched to E85 in my Hyundai I went through a lot of the same headaches your mentioning Just getting to the point of a having tank of 100% E85. Once I was there though it was easier to adjust for the E85 inconsistencies. I couldn't imagine having to always adjust for the E85/91oct inconsistencies. lol

[Rutchard]

All this blending seems to be making the situation more complicated than it needs to be. If you want safety, get a conservative 91oct tune. If you want power, run all e85. If you're already pushing the limits of the stock block and you want safety, why throw an unknown variable into the mix?

[Legend]

I think I am slowly getting talked out of this. I really hate our 91octane but maybe I'll just live with it.