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      01-12-2013, 06:11 PM   #1
thenewrick
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When does the low fuel indicator light appear on 07 E93 335i?

Google search and forum search have failed me. The manual says the reserve tank is 2.1 gallons remaining but I'm not positive if that is when the indicator light comes on. Hopefully someone out there knows for sure!
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      01-12-2013, 06:18 PM   #2
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The light in my car at least (09 328) comes on with a range indication of something like 35 or 30mi, and it's definitely range-driven, not remaining capacity driven. For example, if I'm driving aggressively, the light may come on, but then turn off if I start driving more economically. I think the 2.1gal is an estimation based on typical range at that fuel level.

That said, when my range indicates zero miles, there's still something like a half gallon in the tank. That's based on a specified 16.1gal tank (in my car, anyway) and a fill up at absolutely zero miles range indicated a couple days ago - the car took 15.6 gallons. Granted, the pump was having trouble with early cutoff, but I moved to a different pump to finish the fill, and the car read full after, so I can only assume everything's accurate.
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      01-12-2013, 06:27 PM   #3
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Ah, interesting. I guess it would be something closer to 2.5 gallons remaining when the indicator will typically come on then perhaps.
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      01-12-2013, 06:47 PM   #4
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My low fuel light comes on at 42 to 52 miles
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      01-12-2013, 06:52 PM   #5
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That's right about 2.5 gallons at 19mpg city. Sounds like a pretty solid estimate. That would mean that when the light comes on there's about 13.5 gallons of space for blend. That'd be 4.7 gallons of E85 and 8.8 gallons of 93. To throw another wrench into the equation, I'm pretty sure my city has type 2 E85 for the next few months which is E77 essentially so I reckon about 5-5.5 gallons of E85 currently and the rest 93 would give me about as close to a true 35-65 ratio as I'll get without getting crazy about it.

To be on the safe side I think I'll try 4 gallons of e85 at indicator light and rest 93 and see if any problems arise. If not I'll try for a more true 5.5 gallons of e85 and rest 93 come dyno day.
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      01-12-2013, 07:01 PM   #6
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Quote:
Originally Posted by thenewrick View Post
That's right about 2.5 gallons at 19mpg city. Sounds like a pretty solid estimate. That would mean that when the light comes on there's about 13.5 gallons of space for blend. That'd be 4.7 gallons of E85 and 8.8 gallons of 93. To throw another wrench into the equation, I'm pretty sure my city has type 2 E85 for the next few months which is E77 essentially so I reckon about 5-5.5 gallons of E85 currently and the rest 93 would give me about as close to a true 35-65 ratio as I'll get without getting crazy about it.

To be on the safe side I think I'll try 4 gallons of e85 at indicator light and rest 93 and see if any problems arise. If not I'll try for a more true 5.5 gallons of e85 and rest 93 come dyno day.
You could also do some science, throw a gallon in a can in the trunk, and just run it to dead empty some day.

I'm curious, what are you doing making your own concentration ethanol blend? what do you hope to accomplish by increasing the ethanol concentration above the minimum 10% required most places anyway? Unless you live in brazil, ethanol is pretty empirically the enemy.
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      01-12-2013, 07:33 PM   #7
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Ethanol is used to increase effective octane rating. In turbo cars it's especially noticeable. You can run more boost and advance timings as well as produce less heat while increasing exhaust volume(faster turbo spool).
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      01-12-2013, 07:48 PM   #8
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Quote:
Originally Posted by O HELLA BMW View Post
My low fuel light comes on at 42 to 52 miles
46 seems to be the number for my car which is about 2 gallons so OP, you're correct. I break it down to the "ticks" on the gauge. ~1 tick = ~1 gallon.
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      01-12-2013, 08:19 PM   #9
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Ethanol is used to increase effective octane rating. In turbo cars it's especially noticeable. You can run more boost and advance timings as well as produce less heat while increasing exhaust volume(faster turbo spool).
I realize it increases knock resistance, which I hadn't thought of the implications of for a forced induction engine, that makes sense. But then at the same time, there's only so far you can advance timings and increase compression ratio. That said, I suppose if you've got control over boost pressure, that's fair, you can increase it by taking advantage of the higher KR, and that's not necessarily an engine-controlled parameter.

I guess, mostly, it seems to me that there has to be some pronounced crossover point where the increased knock resistance and following performance gain possibility gets mitigated by the fact that you're effectively removing a lot of energy density from the gas - forcing more air in is great, but if you get twice the charge with gas that's got half the energy in that charge, it's a wash.

I suppose I have no idea where that crossover is, though.

Increased exhaust volume for faster turbo spool makes sense, but do you really get substantially increased volume for less-energy-dense input?

I guess the point is, increased effective octane means you can induct more air and inject a bigger charge, but the composition of ethanol-laden gas would produce less energy and less exhaust for the same volume charge of pure high octane gasoline. So the only increases come from increased charge size, and that'll balance out with the energy decrease at some point.
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      01-12-2013, 08:35 PM   #10
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I'll be using the JB4 "Autotune Map" which can raise boost to as much as 16 psi.

From what I've seen 49% of pure E85 is the safety threshold for the n54 cars. A 35-65 ratio is considered the average safe ratio.

I'm not sure technically how effective it is in one area or another but it does tend to do 2 things consistently; increase power and decrease mpg.

I'm shooting for roughly a 20-80 ratio on first attempt just to see if any issues pop up. If everything goes well I'll try the 35-65 ratio and get a dyno run of that.
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      01-12-2013, 09:04 PM   #11
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Lots of people run e85 blends and get a good increase in power. It's common.
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      01-12-2013, 09:48 PM   #12
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Quote:
Originally Posted by thenewrick View Post
I'll be using the JB4 "Autotune Map" which can raise boost to as much as 16 psi.

From what I've seen 49% of pure E85 is the safety threshold for the n54 cars. A 35-65 ratio is considered the average safe ratio.

I'm not sure technically how effective it is in one area or another but it does tend to do 2 things consistently; increase power and decrease mpg.

I'm shooting for roughly a 20-80 ratio on first attempt just to see if any issues pop up. If everything goes well I'll try the 35-65 ratio and get a dyno run of that.
Yeah, consistent decrease in fuel economy is a given just based on energy density. That's interesting though, I'll be super interested to see your dyno run. Do you have a before for comparison/plan on doing one (with just straight 93)?
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      01-12-2013, 10:03 PM   #13
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I'm hoping to be able to do a stock run, an increased boost map run, and then an e85 run. We'll see how practical it is when the time comes.
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      01-12-2013, 10:05 PM   #14
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Assuming the same dyno session, you could show up on a near empty tank, add a gallon for the normal fuel runs, monitor consumption closely, then make the mix knowing what's now in the tank for 93.
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      01-12-2013, 10:25 PM   #15
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What I'll need to do is show up with a 65% full tank of 93, do my 2 93 runs, then add 4-5 gallons of e85 and go through the gears and do a few non dyno'd runs in 3rd gear to redline to get the auto tune map mostly figured out and then do a proper e85 run. I'm not sure if that'll be prudent though.
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