Can I retune on Pump Gas with E85 still in the tank?

[KadieTSi]

Just curious if I need to get all the gas out of my tank, I have about a 1/6 of a tank of E85 still in my tank right now.

I'm reverting back to my 20psi 91 Octane tune from my 26psi E85 tune for a 1200 mile trip I'm going to be undertaking in my car.

I hear a lot of people say that if I just don't beat on it, I can just fill it with 91 and just let it idle for a few minutes, and then start driving.

Or should I go ahead and drain the current gas?
What would you do?

 

[gofer]

It's no problem changing back to 91 octane with a bit of E85 still in the tank just have your laptop with dsmlink open and connected before you start her back up!

You can get all technical with the global settings and do some math to get everything squared up like it should be, there are three steps to getting your new global fuel settings just follow along below...

1. (% of E85 in the tank x 0.67) + (% of 91 in the tank x 1) = Gas Ratio
2. Injector size x Gas Ratio = Calculated Injector Flow Rate
3. 450 / Calculated Injector Flow Rate -1 = global settings for that tank of gas

Craig (calan) made a great spreadsheet for calculating different E85 blends that I have saved on my desktop to help calculate fuel settings alittle faster. Heres a link to download it and thank calan the next time you see him for making it because it really is awesome... E85 Blends Calculator.

Since you might be a bit confused at the above equation I'll give you an example below going off the info that you gave in your OP. You said 1/6 of the tank is E85 so thats roughly 17%, once your tank is topped off with 91octane you'll have 17% of E85 and 83% 91. Now lets do the math!

1. (0.17 x 0.67) + (0.83 x 1) = 0.94
2. 1600 x 0.94 = 1504
3. (450 / 1504) -1 = -70%

Now you take the -70% and that will be your new global settings in link, just on that tank though. Once you fill up again on 91oct do the math for JUST 91 octane on those 1600cc injectors which would be a -71%.

Really your just nickel and diming those fuel settings as there probably won't be too much of a difference between settings, I'd just set it at -71% like I was running 100% 91oct and forget about it that way you don't have to make more adjustments on the next fill up. On that initial fill up of 91oct I'd suggest doing a 15min log and re-adjust your MAFComp sliders to get your CombinedFT back where it needs to be since it will definitely be off a bit. Doing this you'll get better gas mileage and it will drive a bit better too.

Have a safe trip!

 

[KadieTSi]

It's no problem changing back to 91 octane with a bit of E85 still in the tank just have your laptop with dsmlink open and connected before you start her back up!

You can get all technical with the global settings and do some math to get everything squared up like it should be, there are three steps to getting your new global fuel settings just follow along below...

1. (% of E85 in the tank x 0.67) + (% of 91 in the tank x 1) = Gas Ratio
2. Injector size x Gas Ratio = Calculated Injector Flow Rate
3. 450 / Calculated Injector Flow Rate -1 = global settings for that tank of gas

Craig (calan) made a great spreadsheet for calculating different E85 blends that I have saved on my desktop to help calculate fuel settings alittle faster. Heres a link to download it and thank calan the next time you see him for making it because it really is awesome... E85 Blends Calculator.

Since you might be a bit confused at the above equation I'll give you an example below going off the info that you gave in your OP. You said 1/6 of the tank is E85 so thats roughly 17%, once your tank is topped off with 91octane you'll have 17% of E85 and 83% 91. Now lets do the math!

1. (0.17 x 0.67) + (0.83 x 1) = 0.94
2. 1600 x 0.94 = 1504
3. (450 / 1504) -1 = -70%

Now you take the -70% and that will be your new global settings in link, just on that tank though. Once you fill up again on 91oct do the math for JUST 91 octane on those 1600cc injectors which would be a -71%.

Really your just nickel and diming those fuel settings as there probably won't be too much of a difference between settings, I'd just set it at -71% like I was running 100% 91oct and forget about it that way you don't have to make more adjustments on the next fill up. On that initial fill up of 91oct I'd suggest doing a 15min log and re-adjust your MAFComp sliders to get your CombinedFT back where it needs to be since it will definitely be off a bit. Doing this you'll get better gas mileage and it will drive a bit better too.

Have a safe trip!

Great! Yeah that's the spreadsheet I used when I initially tuned it on E85, its been great! I never imagined I'd be able to self tune my car into the 11's, and it's still a really 'safe' tune, I could stand to add about another 4 degrees of timing based on others setups/advice but I'm a chicken

Anyways, I'll follow along what you said, thanks a ton!

Nothing has broke aside from my transfer case yet since my build, so hopefully I go problem free for this trip!

 

[gofer]

Your welcome and E85's amazing isn't it? Just don't go WOT on your E85 tune, if your a bit lead footed and can't stay out of boost I suggest running your stock DA maps and zero'ing your sliders just for the trip. Then once you get E85 in the tank again reload your old settings, they might not be too aggressive when your running E85 but 91oct hates timing advance and boost so you might be pushing it.

In my experience tuning my car on the dyno where you can see the power gains from advancing timing, turning up the boost, and leaning out the AFR's you'd be surprised at how little those 4* of timing advance gets you in hp/tq. For example on my car 20* of timing advance I was putting 441awhp down on the dyno but showing signs of detonation. But at 17* degrees I was putting down 437ahwp and NO detonation and whats 4 hp really going to get me other than a dead motor? Your tune might be perfect and the good news is you aren't running it too aggressive so you've got an 11sec car that will last!

 

[RollinBigPower]

This is an amazing table! Takes most of the guesswork out of tuning for E85. Absolutely great!

It's no problem changing back to 91 octane with a bit of E85 still in the tank just have your laptop with dsmlink open and connected before you start her back up!

You can get all technical with the global settings and do some math to get everything squared up like it should be, there are three steps to getting your new global fuel settings just follow along below...

1. (% of E85 in the tank x 0.67) + (% of 91 in the tank x 1) = Gas Ratio
2. Injector size x Gas Ratio = Calculated Injector Flow Rate
3. 450 / Calculated Injector Flow Rate -1 = global settings for that tank of gas

Craig (calan) made a great spreadsheet for calculating different E85 blends that I have saved on my desktop to help calculate fuel settings alittle faster. Heres a link to download it and thank calan the next time you see him for making it because it really is awesome... E85 Blends Calculator.

Since you might be a bit confused at the above equation I'll give you an example below going off the info that you gave in your OP. You said 1/6 of the tank is E85 so thats roughly 17%, once your tank is topped off with 91octane you'll have 17% of E85 and 83% 91. Now lets do the math!

1. (0.17 x 0.67) + (0.83 x 1) = 0.94
2. 1600 x 0.94 = 1504
3. (450 / 1504) -1 = -70%

Now you take the -70% and that will be your new global settings in link, just on that tank though. Once you fill up again on 91oct do the math for JUST 91 octane on those 1600cc injectors which would be a -71%.

Really your just nickel and diming those fuel settings as there probably won't be too much of a difference between settings, I'd just set it at -71% like I was running 100% 91oct and forget about it that way you don't have to make more adjustments on the next fill up. On that initial fill up of 91oct I'd suggest doing a 15min log and re-adjust your MAFComp sliders to get your CombinedFT back where it needs to be since it will definitely be off a bit. Doing this you'll get better gas mileage and it will drive a bit better too.

Have a safe trip!

 

[gofer]

Thanks RollingBig I'm glad someone else got use out of that post too!

I forgot to mention, at least in my cars case, it wasn't very "flexible" in terms of switching from E85 to 91oct even after I did the changes to my fuels global settings. I suggest kicking on the fuel pump in dsmlink after you fill up and let that E85 thats in the lines cycle through for a minute or two so you get some 91oct to the rail.