Fuel level input accuracy? - E85 mixing

[MrBatou]

Hey guys, I was just wondering if anyone had experience showing that the fuel level input is actually reading 12.4 gallons at 100% or is it maxing out at some value that's under 12.4 gallons? I came up with some math that shows how to actually hit 40% ethanol content using E85 (knowing that it can be anywhere between 51% and 83% ethanol). However, it seems that when I calculate how much fuel is in the tank before filling it up ([fuel level input]% x 12.4]), then add the amount that the gas pump puts in until auto-shutoff, the result is less than 12.4 gallons and my AP reads 100% on fuel level input. Maybe the ground is not level but I am showing over half a gallon less than the 12.4 max tank size after filling up.

 

[TyphoonFiST]

When i was E30 i would Hit the Gas/re-fuel light ...Then Go to get Gas of 3 gallons of E85 and the rest 93 Oct. Which was usually around 8-8.5 Gallons to get e30. Now i just have a Fuel-it system with the sensor and the App on my phone that has bluetooth to tell me what i'm sitting at for Ethanol content. e50-e60 is the reverse 8 gallons of e85 and about 2.5-3 gallons of 93 oct.

 

[MrBatou]

I have mix instructions from my tuner that I’m following so I should be covered on that front. I was just trying to figure out the accuracy of 100% fuel level input on the AP. It seems it is off by about half a gallon from what I can tell, assuming it is accurate at low levels. I’m sure the gas station pump is accurate also.

 

[kivnul]

About 1/2 a gallon under is about what I have noticed. You can either tweak your math to compensate, or just not fill that 1/2 gallon at the end so that your numbers are what you calculated.

 

[esp_martin]

Hey guys, I was just wondering if anyone had experience showing that the fuel level input is actually reading 12.4 gallons at 100% or is it maxing out at some value that's under 12.4 gallons? I came up with some math that shows how to actually hit 40% ethanol content using E85 (knowing that it can be anywhere between 51% and 83% ethanol). However, it seems that when I calculate how much fuel is in the tank before filling it up ([fuel level input]% x 12.4]), then add the amount that the gas pump puts in until auto-shutoff, the result is less than 12.4 gallons and my AP reads 100% on fuel level input. Maybe the ground is not level but I am showing over half a gallon less than the 12.4 max tank size after filling up.

i don't have a dizzy or Fuel-It ethanol gauge so when i go E30 I always overshoot to be safe. by a lot. similar to @TyphoonFiST i would wait for the low fuel light, put in 3+ up to 4 gallons of ethanol and fill the rest up with 93OCT. if i was low on fuel but not on empty? i still put 3 gallons of ethanol in the car and filled the rest with 93OCT. half tank left? 2 gallons. i know the car's tune has no problems in the E30-E50 range. but below E30 that knock limit might get hit at WOT. I'm not going to risk that just so i can get a few extra MPG from the tank.

i'm guessing your math equation always assumes the ethanol content is at 51%?

edit: the station i go to is the only ethanol fuel option within 30 miles so people test it and post it on google maps pretty often and it's always near 80%

 

[NATYPE]

i don't have a dizzy or Fuel-It ethanol gauge so when i go E30 I always overshoot to be safe. by a lot. similar to @TyphoonFiST i would wait for the low fuel light, put in 3+ up to 4 gallons of ethanol and fill the rest up with 93OCT. if i was low on fuel but not on empty? i still put 3 gallons of ethanol in the car and filled the rest with 93OCT. half tank left? 2 gallons. i know the car's tune has no problems in the E30-E50 range. but below E30 that knock limit might get hit at WOT. I'm not going to risk that just so i can get a few extra MPG from the tank.

I'm pretty much doing exactly this. Similar estimations, tolerances, guess work in the moment etc. It's been painless. I saw a tip on here somewhere to watch your fuel trims at WOT to get a sense for where your ethanol content is after the tank has been mixed etc. The Sheetz around here have never drifted off 75-83 percent and I'm overshooting as well. Likely somewhere around E40 all the time.

 

[kivnul]

Question then, If you are right at the fuel/air limit at WOT using known E30, is there a consiquence to having E40 in the tank?

 

[esp_martin]

Question then, If you are right at the fuel/air limit at WOT using known E30, is there a consiquence to having E40 in the tank?

for me, i'm only talking about the stock turbo on an e30 tune. as far as i know all e30 tunes on stock turbo aren't at the fuel/air limit, they're at the turbo limit. the tiny turbo and the knock are the ceiling. the engine isn't at the fuel/air limit. i don't even think it's close to the limit. i know dizzy has an e40 tune for the stock turbo if you install a 7PSI WGA. but i *think* that's more for helping the stock turbo breath past the 5500RPM limit then for putting out more HP (i think it still punches more torque though)/

for big turbo applications that run ethanol tunes without the uprated bosch injectors, i'm not sure though. because then you are hitting the ceiling of how much fuel the OEM injectors can put out.

 

[Erick_V]

The best way I've learned to randomly fill up on E is to follow the 1/4 markers on the fuel gauge which would have 4 lines (obviously). If the car is at half a tank (2/4 lines) I fillup with 2 gallons of E and the rest with 93. If my tank is on almost 0 miles to empty I have 4 marks so I would do 4 gallons of E and the rest 93. I have an ethanol content gauge and doing that usually lands me in the E30-E35 range.

Edit. I know tuners say when the fuel light comes on (50 miles to empty) put 3 gallons and the rest 93. If you want to do that go ahead but being that I'm anal and have an E gauge I adapted my fill-ups to that

 

[kivnul]

for me, i'm only talking about the stock turbo on an e30 tune. as far as i know all e30 tunes on stock turbo aren't at the fuel/air limit, they're at the turbo limit. the tiny turbo and the knock are the ceiling. the engine isn't at the fuel/air limit. i don't even think it's close to the limit. i know dizzy has an e40 tune for the stock turbo if you install a 7PSI WGA. but i *think* that's more for helping the stock turbo breath past the 5500RPM limit then for putting out more HP (i think it still punches more torque though)/

for big turbo applications that run ethanol tunes without the uprated bosch injectors, i'm not sure though. because then you are hitting the ceiling of how much fuel the OEM injectors can put out.

It was more of a generic question. I concur it is not a possiblity with the OEM turbo. I have an x47r and it is an issue for me when its around 45 degrees out.

 

[Zormecteon]

This is all under the assumption that adding gasoline and ethanol the total created is the total off the two different liquids. .. I'm not a chemist, but I believe that the total is LESS than the amount of each added because of the differing molecular structures...

I'm reminded of an old professor who fills a clear jar with marbles then asks if the jar is full. The students all say "yes". Then he adds pebbles and asks is the jar NOW full, and again gets the same reply. The he adds sand. Same deal. The students are now even more sure that it's full. Then he adds water. This time they are certain that it is indeed full to the brim... ....

Then he adds alcohol. ... ... There is indeed space between the molecules of water!

 

[esp_martin]

This is all under the assumption that adding gasoline and ethanol the total created is the total off the two different liquids. .. I'm not a chemist, but I believe that the total is LESS than the amount of each added because of the differing molecular structures...

I'm reminded of an old professor who fills a clear jar with marbles then asks if the jar is full. The students all say "yes". Then he adds pebbles and asks is the jar NOW full, and again gets the same reply. The he adds sand. Same deal. The students are now even more sure that it's full. Then he adds water. This time they are certain that it is indeed full to the brim... ....

Then he adds alcohol. ... ... There is indeed space between the molecules of water!

i think the better comparison is alcohol proof in bourbon. we're not concerned about the total volume so much as the ethanol content within.

i agree about still guessing though and we all just need to get one of those gauges, lol

 

[Raziel510]

I've had a innovative motorsports ethenol gauge for about 3 years already and like Erick_V said follow the 1/4 marks. If my refueling light is on I usually put around 3.5 ~ 4.0 of E85. It always fluctuates from E30 ~ E40 cars been running good with all the percentages.

 

[cidsamuth]

I think you guys are trying to hard all in the name of filling the tank to 100%. If you walk away from that idea, using E mixes is much easier.

Assume you can fit 1-2 gallons less than the gauge implies you could. So, as an example, if at 1/4 tank left, plan to put in only 7 gallons. That way, you know exactly how much fuel is going in.

Once you test for E content at the pump you’re using, do the math for 7 gallons and put only 7 total gallons in. You won’t get the tank full, but you will reasonably ensure you’re getting the E% you want.

And you guys who think “overshooting” the E% is the safe way to do it might not be as conservative as you think; more E means cooler temps but also means a leaner AFR.

 

[kivnul]

"..... And you guys who think “overshooting” the E% is the safe way to do it might not be as conservative as you think; more E means cooler temps but also means a leaner AFR.

I think this answers my above question. Since I am already at the limits of AFR, overshooting to something like E35 might be a bad thing.