RS5 and E85 official thread

A5/S5/RS5
#6

Ha! No worries at all. Want to go in eyes wide open.

Just a clarification on the A4 pump though. It’s literally the same pump as the RS5 pump, just has different seals/bearings for use with ethanol. Both flow the exact same amount of fuel and it’s a drop in replacement. So you’re not loosing any flow by switching to this LPFP.

Granted, with ethanol I’ll need more fuel altogether but it sounds like it’ll work fine with E40 and won’t get eaten up by ethanol which has no lubricity. I guess I could also just run a bit of “premix” in there like I did during my rotary days!

#7

Yes I suck at making the point. The point that I sucked at making was that. The A4 that has a pump that allows it to run E85 has enough head room to run a high powered high revving V8. If that’s the head room it takes to run a 4 cylinder. how much more head room would we need to add to the pump to give the V8 the same… Regardless E40 you won’t have any issues.

Sorry I sucked at making my point.

#8

Just to clarify, are we saying that TYPICALLY we’re OK to run E40 without modifications? Have the S4 guys seen any problems long term with E40? I’m sure the A4 flex pump would be a peace of mind thing, but I’m curious none-the-less.

#9

Maybe but with tuning. You can’t just run an E40 mix with no other tuning. The in-tank pump would be peace of mind. We can check in with the S4/S5 guys to see what, if any, long term problems they may be having as a result of using ethanol.

#10

So the S4 guys seem to be able to run E40 but need upgraded HPFP’s (Autotech) for E85. Some years are better than others, pre and post facelift.

I’d say it definitely needs testing to see if the high pressure pumps can handle the additional flow. I think we could get by with E40 but it’s just a guess at this point.

Dear JHM.,
Please make upgraded internals for our high pressure fuel pumps.
Sincerely,
RS5 people everywhere

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#11

You know, thinking about E40, I’d have to look up a converter but the octane would probably be about the same as 93 premium here in the states.

Doing a bit of research on the flex fuel pump and it actually may have more headroom than the OEM pump. Not confirmed yet.

#12

Well our standard fuel is E10. As most gas stations have 10 - 15% ethanol in them already at the 93 octane level.

Assuming your starting with 93 octane with a rating of E10 and then your adding another 30% ethanol to that base your going to be bumping the octane quite a bit.

#13

Ok so thinking about this like this and using the math from the race gas thread…

Now check my math just to make sure and I’m padding the stats a little bit there. Since our standard 93 octane is E 10 already. I’m going to just add the difference of E content left to make E40. Here is how my math works out.

So E10 = 93 octane
To keep the math simple lets use 10 gallons of gas

So take 7 gallons of 93
Then since we already have E10 we want to get to E 40 we can add 30% more E content or 3 gallons out of 10 gallons.

So 3 gallons of E95 now keep in mind this is E95 not E100 but the octane content of E85 = 108

Doing the octane math works out like this.

7 gallons of 93 octane 7 x 93 = total of 651
3 gallons of 108 octane 3 x 108 = total of 324
651 + 324 = 975 / 10 = 97 octane… And since we used E85 not E100 we’re I don’t think even at a true E40 mix

Now that is crude math but you can see basically adding 3 gallons of E85 to 7 gallons of 93 bumps the octane up quite a bit enough so that its going to give you all the benefits your looking for while staying in a really safe zone for everything

#14

Oooooor…use an online E85 calculator!
https://www.brewcityboost.com/about/ethanol-calculator/

Basically, using that calculator, it’s right around 95-96 octane, E40. Not really worth it IMO unless runningE40 nets a nice drop in EGT’s (exhaust gas temperature). Lower EGT’s, cooler engine, ability to run more timing.

#15

using the link you posted gave the same results as my math above. When started at the same point.

So my math is good at least…

But my math gives it a content of E33 = 97.5 octane

E33
E331282×552 44.9 KB

Here is almost E40 / Its E37 = 98.5 Octane

E37
E371263×560 45.3 KB

E40 is basically 100 octane.

E41
E411335×557 44.8 KB

So IMHO. E40 is basically 100 octane, Now keep in mind the mix ratio is based off mixing 93 octane and the fact that E85 is 108 octane not 100

#16

You know what…when I did it, I used the default 100 octane for E85 hence the lower numbers.

#17

I think it’s worth pointing out that on the other forum, there’s a Polish guy that states in Poland their standard is 95-98 octane (or at least that’s how I’m interpreting it). But when using Shell Racing fuel (100 octane), the ECU started giving him trouble with a EPC light.

I wonder if a simple tune would allow us to run E40 without much change in hardware. It’s be nice if this guy was tracking his results… wishful thinking.

#18

He may not have a tune that can take advantage of 100 octane. The Count and I were just discussing octane and ethanol. Short version, the more octane there is, the slower the flame front (it ignites more slowly). So instead of using all the energy contained within the initial ignition to push the piston down, you’re actually pushing it out the exhaust or creating the big bang at a point where the combustion cycle can’t use the energy released. I’m sure this probably sends the knock sensors into a tizzy. Probably throws off the a/f ratio too.

#19

Europe 95 - 98 = North America 90 = 93 So its not the same as in the states. It’s not our version of 95

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#20

Tested the ethanol at the local station and it came back E73 which isn’t bad for winter. Was hoping they never let it drop below E85. I may end up waiting for spring so I’m not constantly having to recalculate and measure the ethanol content.

#21

E73 isn’t bad at all most winder blends end up being E60. But if you do 7 gallons of 93 and add 4 gallons of E70 your still at 97 octane. So not too bad. Better than what your working with right now.

The fact that the e- content is lower might be a good place to start.

#22

E40 no problem at all in my experience. It goes faster. I have run the car with up to e85 even in winter. The fuel consumption goes up as it should. I havent pushed the car that hard with only e85 but yes in my experience with no tune there is probably little to be gained from it (for the reasons mentioned: octane more fuel needed to be pumped in). At somewhere between e40 and e50 you start getting check engine light at some point bank 2 oxygen sensor.

No issues at all though thus far.

#23

Hey TontoLoid, welcome and thanks for sharing your experiences, A few questions naturally as I embark on this myself once life goes back to being somewhat normal.

Have you done any logging to look at fuel trims by any chance? The BTU of E85 is less than that of gasoline so you should need quite a bit more to make the same power, hence your consumption rate going way up.

The check engine light is probably because the fuel system can’t push enough fuel within the parameters dictated by the ECU. May be out of range so to speak.

In winter, the actual ethanol content fluctuates and goes down. In some areas the content will drop down to E60. My “winter” blend registered at E72 and I’m waiting for the summer blend of E85 before experimenting as I don’t want to constantly sample and have to recalculate ratios to achieve E40.

On the fuel injector front, I know lots of the RS3 guys are now having injector issues due to using straight E85. I just replaced mine and I don’t want to do it again any time soon as it isn’t cheap! I’ll probably stick with E40 and a tune.

Do you by chance ever add any additives like Techron to the tank to help clean the ethanol residue? They generally mix the ethanol with 85 octane no detergent package gas (crappy gas in other words!). My plan was to use the flex fuel pump to mitigate some of this and adding Techron every other tank or so.

#24

Thanks! Happy to be here.

Havent analyzed things properly would certainly if i wasnt in one of the few countries not in lockdown.

Build up on the injectors was said years ago to be due to ethanol not being compatible with some additive in the gasoline to prevent it. Therefore the cleaner was added with the fuel. It is some kind of gunk being formed (not carbon). The cure was said to be a tank of regular gasoline every 5 full tanks or similarly often.

As for the ethanol content I have experienced no calibration issues. Who know maybe pushing the set button per the manual will speed up the calibration but I am fairly sure that by the time you have warmed up the car you’ll be golden.

As the exhaust oxygen sensors, due to e85 containing more oxygen, will continue pumping in gas you will never run lean. I have never ran rich either. If anything my fuel consumption has been slightly better without less power only thing I have experienced is more power. Especially in hot conditions with slightly dense air you should see an improvement vs gas. The typical scenario of failing injectors on cars like ours must be driving it hard perhaps or bad gas. Mine are perfectly fine after varying between various ratios of E, 95,98,100,102 octane. Havent been putting in premium gas that often although doing it now and then will help the cleaning.

#25

In response to the car being allergic to high octane :rofl: :see_no_evil: that must be crappy gasoline then the premium fuel additives/better performance due to higher octane starts cleaning thing;. build up comes off

The only serious accounts I have is a b8 s5 that is the v8, on a french e85 forum. Hes given multiple accounts of it all he has done is the adapter from the ECU controlling the pump/injectors. Over 100,000 miles no issues except early on the clogged injectors (replaced under warranty/goodwill). The wear as you’ll get maybe 10 % more power that will mean more wear. Need to halve the oil change intervals as there is some metal in engine oil incompatible with ethanol. I believe the tests in a paper I read regarding the gunk on the injectors were carried out in western europe where the fuel is mostly the same ie has the same additives. Depends a bit on which season.