Yeah my guys with starting issues r on an aem and e85.
And that's another thing they say is holding me back but I think the stock ecu is as good with tephra mod.

 

stock ecu isn't holding anything back once you're using speed density.

 

This statement is one I've heard lots of times - though usually from people who I am less inclined to pay attention to than I am you.... so have just ignored it. What I do know is that the difference is the fuel/air ratio for stoich on E85 is like 49% higher than for petrol, which would mean to me (and so far my experience with tuning as well matches this) that to hit the same target lambdas on E85 the fuel system would need to flow 49% more fuel than when running petrol. By my rough calculations I'd expect about 61% more to be moved to provide the equivalent lambda on E98 versus petrol.

Is there something I am missing here? I have assumed when people say 30% instead of 49% that it isn't just that they are running way leaner mixtures on E85 - but I can't get my head around it otherwise.

Cheers

 

Ima try e85 maybe this spring and if not then ima sell my turbo and pick up a 6766 and hope the power goes up that way.

 

Somehow your values got reversed. Stoich for E100 (for reference) is 9:1 which is 61.2% of gasoline's stoich value. The 30% value is for E85, E100 ends up being closer to 40% but you can run it leaner safely and still manage the 30% rule. For instance my car at full power on the last turbo setup made peak power at 39.5psi and a 12.8 AFR.

Aaron

 

I don't think I did? If anything to me it looks like you got it backwards, as what you described means you use ~30% *less* fuel to convert from E85 to petrol.... but this thread is talking about going the other way.

I deliberately did my calculations for Fuel/Air ratio as I wanted to compare masses of fuel required for a given volume of air so I could determine how much more needs to be added for ethanol blends to scale for the new stoich value.

ie:

1
----- = 6.8% petrol
14.7


1
---- = 11.1% ethanol
9.0


1
---- = 10.1% E85
9.86


So to determine how much more (or less) E85 needs to be used to mix with an equivalent mass of air versus petrol:

10.1 FARst for E85 / 6.8 FARst for Gas = 1.49x more fuel for E85

Or

11.1 FARst for Ethanol / 6.8 FARst for Gas = 1.63x more fuel for Ethanol

Or just for fun....

11.1 / 10.1 = 1.1x more fuel converting from E85 to "straight" ethanol

All fairly rough calculations to save throwing more numbers around than I needed to explain it, but that's the general way I work this kind of thing out and I built my first flex fuel trim table using my hairbrained maths and started the car in question and poured from 0% to 80% ethanol without needing to adjust anything to maintain my intended target lambda with closed loop off I must have got something right - unless the wideband and ECU were playing tricks to make me look silly

This is why it vexes me when I see people consistently say ~30% more fuel for ethanol is required, as I at least *definitely* need ~49% more fuel to maintain an equivalent lambda reading.

Sorry to be pedantic, but given people may select fuel systems (ie, myself, OP, other randoms who find this thread) based off these things it's something that would be ideal to get right

 

Having run E85-E100 for the last 5 years I have plenty of real world experience for what it takes to make it work. I know how it maths out when you tune them, what fuel concentration will do what, etc. Believe it or not, I have practice with E85-E100 and selecting appropriate fuel systems

 

Clearly, you have tuned >800whp EVOs - was not implying otherwise, just trying to discuss it seeing as it is on topic and this is an open forum so the picture is clearer... how about a nice short quotable question you can say yes or no to

What you are saying is that you may need ~49% more fuel to maintain the same lambda on E85, but you can get away with running it leaner on boost which allows you to get away with only 30-40% larger fuel systems?

Clarifying that would be hugely appreciated as it is something which has irked me for some time. Thanks

 

And for whatever reason my tuner tells me to stick with 110 over e85!
Sayin there ain't that much power gain in the switch.
From what ur sayin with 40% more fuel sounds like I'd make a lot more power?

 

it uses 30-40% more fuel WOT. and yes you will irace2much.

 

Lith, I think its how you are doing the math. When you do the division with the actual Stoich value it works out.

E100 - 9/14.7= 61.2% - 40% change difference
E85 - 9.8/14.7= 66.66% - 33.3% change difference

When I switch from gasoline to E85 I take the global value (injector scaling) and multiply it by 0.7 and the car is almost always exactly on the trims, cruise is correct, and WOT is correct.

Irace2much- He is dead wrong. Go run 50psi on 110 with 10.5:1 compression and 18* of timing and let me know how that works out.

 

^^ not too good! Lol e85 takes 30% more fuel than gas. Fact! No room for argument......

 

Thanks, TScompusa :-)

Ahh I think I see what is happening here (assuming above you mean you actually DIVIDE by .7, or even better - .67). If so, that totally matches my maths - just looking at it the other way around, and where the source of confusion would be. Getting 66.66% doesn't mean you add 33.3% to your petrol map, it means your final E85 map is missing 33% of it's total. Sounds like the same thing, but think of it in terms Bill Gates losing 33% of his money versus yourself becoming 33% richer.... I'd say you'd rather get the 33% that Bill Gates lost than add your own 33%

Divide 1 by 0.67 with your calculator to see what scale you apply to go from a 9.8 stoich to a 14.7 stoich

 

I multiply by 0.7 ... the asterisk function is multiply in ECUflash. Its how the number goes though in the software, a lower number is richer for a given injector. I think we are agreeing in radically different ways.

1000cc on gas scaling would be 700 (1000 x 0.7) for E85, but to lean it out for Gasoline it would be 700 x 1.425 which is closer to how you calculated.

Per the fuel system though I can still think of several examples where my math is still 30% difference (albeit 30% IDC). Some depends on pump size (flow) and fuel pressure + boost (total required) though as well. What I can do with 1450s on E85 (unless otherwise noted) let's say is a good example-

1450s + single 255 (2.0L) = 520whp at 30psi maxed out 105-110%
1450s + twin 255 (2.4) = 762 at 32psi maxed out 105-110%
1450s + twin 044s (2.4) = 748 at 41psi maxed out 105-110%
1450s + twin 255s + Q16 (gasoline) on a 2.0L = 780 at 44psi and 83% IDC

 

Yeah no doubt there will be other variables which will affect it but it sounds like we are on a similar page - just going about it in different ways

Would actually be really interesting to see tune a car tuned on Q16 then on E85 with no other differences (so it's the same amount of air going in) then compare power level etc. Another topic, though

No doubt E85 will end up needing around 30-35% more fuel than Q16 for similar lambda with all other things being equal given if I remember rightly stoich for Q16 is only around 13.3-13.4.

Cheers for sharing experience etc on this kind of thing, by the way. I've played with ethanol tuning in bits and pieces over the last 5 years but in no way as extreme or as much as you have so its really a good to be able to speak to people who have made cars make 800+whp reliably