Mixing E85 and Pump Gas? Wait a few minutes! Literally.

[chadillac2000]

I've spent the past few years mixing E85 and 93 octane at the pump in both my 535i and 135i. As soon as I started doing this, I always wondered exactly how long to let things mix before getting deep into the throttle. I naturally sway towards the safe side, so I'd always wait 5-10 minutes before assuming the ratios were consistent in the tank.

After recently installing Fuel-It's upgraded fuel lines, ethanol sensor, and ethanol analyzer, I've been able to have a live view of how much ethanol is actually running into my engine. Now that I've filled up a few times with the new equipment, I've kept a close eye.

From almost completely empty (around 1/16th of a tank of E40 remaining -- confirmed using the ethanol analyzer), I added 7 gallons of 93 octane. For almost 2 full minutes (over a mile of driving), the sensor detected E40 before finally dropping and settling to somewhere around E13. Once I'd made it to my E85 station, I topped off the tank.

Again, it took almost 2 full minutes of light driving for the sensor to start detecting the increased ethanol content before settling again around E40.

So the moral of the story is, if you have previously been running a straight pump gas, and then add a few gallons of E85, 2 minutes of light driving, perhaps a little less if moderate driving, seems to be the point in which you're getting the updated ethanol ratios to your engine. I just wouldn't recommend going WOT straight out of the station relying on the fuels to already be mixed as soon as they hit your tank.

[dtla1]

That's why I go to a station that has Pump gas and Ethanol right next to each other.

[chadillac2000]

Originally Posted by dtla1

That's why I go to a station that has Pump gas and Ethanol right next to each other.

I do too.

This was for experimentation purpose to see how long it took before the previous ratios of ethanol in your tank turned into the ratios you just pumped in. Not as important if you're previous fill-up was with the same ethanol ratio, but if you're changing ratios, or going from straight pump to an E85/93 blend, just stating that it takes around 2 minutes or so for that to make its way to the sensor.

[houtan]

Thanks for the info

[Thewind727]

does anyone know a good calculator to use to figure out what the ratio is

[all4bspinnin]

Originally Posted by Thewind727

does anyone know a good calculator to use to figure out what the ratio is

Cobb had a decent ethanol mix chart. You may be able to find it on google or in the Cobb BMW tuning guide at the bottom.

The OP is exactly right. ALWAYS watch your timing corrections and STFTs. Go easy on the throttle after running a mixed blend at first. It takes many miles for it to blend completely.

It may seem overkill but I always fuel up at a pump with e85 and 93 next to each other and I always wait until the next day before driving aggressively.

[Thewind727]

Originally Posted by all4bspinnin

Cobb had a decent ethanol mix chart. You may be able to find it on google or in the Cobb BMW tuning guide at the bottom.

The OP is exactly right. ALWAYS watch your timing corrections and STFTs. Go easy on the throttle after running a mixed blend at first. It takes many miles for it to blend completely.

It may seem overkill but I always fuel up at a pump with e85 and 93 next to each other and I always wait until the next day before driving aggressively.

Thank you

[chadillac2000]

Originally Posted by all4bspinnin

The OP is exactly right. ALWAYS watch your timing corrections and STFTs. Go easy on the throttle after running a mixed blend at first. It takes many miles for it to blend completely.

It may seem overkill but I always fuel up at a pump with e85 and 93 next to each other and I always wait until the next day before driving aggressively.

I respect playing it safe, but definitely overkill. The whole point of this thread was to show people that it only takes 2 minutes or so at very light driving (shifting at around 3,000 rpm) before the correct ratio begins flowing into the engine.

[ShocknAwe]

This is thanks to fuel line length. Mixed stuff is in the lines already, when you fill up, it mixes the tank, takes a couple miles for the lines to draw fully from the tank to engine w/ new mix.

Also why you can drive on a totally empty tank for a while before misfires start.

[chadillac2000]

Originally Posted by ShocknAwe

This is thanks to fuel line length. Mixed stuff is in the lines already, when you fill up, it mixes the tank, takes a couple miles for the lines to draw fully from the tank to engine w/ new mix.

Also why you can drive on a totally empty tank for a while before misfires start.

Precisely. Fuel-It explains below.

Originally Posted by Steve @ BMS/Fuel-It!

Fuel is constantly circulating with the jet pumps, return, and transfer from the driver's side. It mixes very quickly. It's mostly the fuel in the lines that you have to consume prior to your sensor reading the new ethanol content. At idle you use very little fuel.

[Dylanize]

I <3 E85.

That's all I have to contribute to this thread. :P

[PhxN54]

Originally Posted by ShocknAwe

This is thanks to fuel line length. Mixed stuff is in the lines already, when you fill up, it mixes the tank, takes a couple miles for the lines to draw fully from the tank to engine w/ new mix.

Also why you can drive on a totally empty tank for a while before misfires start.

^ Bingo

Thanks for the ~2min info OP.

[all4bspinnin]

Originally Posted by chadillac2000

I respect playing it safe, but definitely overkill. The whole point of this thread was to show people that it only takes 2 minutes or so at very light driving (shifting at around 3,000 rpm) before the correct ratio begins flowing into the engine.

I wish that was the case in my observations. After driving several miles for roughly 10 minutes Ive seen slight timing corrections. The next day after using that exact same tank with the engine at same temp, no corrections. But what works for me, may not be the exact scenario with other cars. Those I've tuned have experienced this as well.

The key is to make sure your scalar table and blends are on point. As long as you're watching your timing corrections and know when the car is correcting, you know where to go from there.

[CRYA]

Noob question on E85. I just learned that I'm getting a new gas station in town that will carry e85. I've never played with the stuff before. I'm also about to get a new tune from MHD/Wedge. Aside from the tune, can I literally just mix in the e85 and the 91 oct at the pumps and go? No further mods *required?

[Thewind727]

Originally Posted by CRYA

Noob question on E85. I just learned that I'm getting a new gas station in town that will carry e85. I've never played with the stuff before. I'm also about to get a new tune from MHD/Wedge. Aside from the tune, can I literally just mix in the e85 and the 91 oct at the pumps and go? No further mods *required?

thats what i do, i run the e40 ots map with a 50/50 blend of 93 and e85, just keep an eye on your lpfp #s as long as they stay good and in an acceptable range you should be good.

[Rob_BMW_PNW]

Originally Posted by Thewind727

does anyone know a good calculator to use to figure out what the ratio is

https://www.intercepteft.com/calc.html

It is basic math though

[Rob_BMW_PNW]

Originally Posted by Thewind727

thats what i do, i run the e40 ots map with a 50/50 blend of 93 and e85, just keep an eye on your lpfp #s as long as they stay good and in an acceptable range you should be good.

2k+ psi at wot is the good number for HPFP right?

[Thewind727]

Originally Posted by Rob_BMW_PNW

2k+ psi at wot is the good number for HPFP right?

yes but the lpfp is where you can really see if its struggling anything below 50 when i've run the e40 map and i can really feel the power fade away.

[Thewind727]

Originally Posted by Rob_BMW_PNW

2k+ psi at wot is the good number for HPFP right?

http://datazap.me/u/thrwind727/log-1...a=4-6-16-17-23

this is a 4th gear dyno pull with about an e55 mix on the v7 e40 map my lpfp stays just barely above 50 toward redline and my hpfp only starts to dip pst 2100 after 6k rpms which is where i would normally shift so im ok with it tanking after that lol.
also both lpfp and hpfp only have about 3k on them, just had them replaced by bmw

this was a 420whp 475wtq run so i was very pleased