Any reason we can't blend in some e85 for knock resistance?

[05yellowgt]

I was just thinking of this today, why the same lambda on the 02s can be used for fuel no matter the ethanol content.

The 02 sensor measures the air/fuel ratio AFTER it's burned in the combustion chamber, obviously. Yes, more of the fuel goes INTO the cylinder when you run more ethanol content, but the same amount comes out because all the extra (compared to pure gasoline) is burned in the combustion cycle. Is this correct or am I way off?

There is a greater total volume of air/fuel going in, and more coming out. The O2 sensor is just reading the amount of oxygen left in the burnt mixture.

 

[05yellowgt]

I could swear the mixing of e85 in with his 92 octane was to prevent the car from pulling timing when it gets hot/heat soaked. . . not to add more timing. . . he wants to see peak timing all the time, and the 2-3 gallons of e85 would let that happen correct?

It helps with one variable of power loss due to the summer heat, the buildup of heat in the combustion chamber that can lead to detonation. It helps prevent hot spots forming in the combustion chamber, or the spark plugs being unable to absorb enough heat and turning into glow plugs. It isn't going to overcome the ECU pulling timing from the coolant temperature getting to high, or the AIT sensor reading from causing the ECU to do the same thing (the AIT sensor is sampling the temp of the air prior to the port injector, therefore not seeing the cooling effect that the fuel has on the air charge).

 

[KrisR]

Just a quick update, got some smoke coming out of the tailpipes now and compression in #8 is down......





















Just kidding, everything's great. The last fill-up I tried 5 gallons of e85 in the tank this time (I had run two tanks of pure gas in it for a long road trip so there was basically zero e85 in it previously), so this time it was basically a 30% e85 / 70% gasoline mix, and I see no benefit as far as knock resistance with this mix versus the 20% mix. So this basically confirms what "cbrtx" said above, keep it at 20% or so and get the benefits with the least amount of fuel trim adjustment.

Fuel trims are about +10% with the 30% mix versus around +7-8% with the 20%, both of which are what I expected.

 

[MikeT]

Just a quick update, got some smoke coming out of the tailpipes now and compression in #8 is down......





















Just kidding, everything's great. The last fill-up I tried 5 gallons of e85 in the tank this time (I had run two tanks of pure gas in it for a long road trip so there was basically zero e85 in it previously), so this time it was basically a 30% e85 / 70% gasoline mix, and I see no benefit as far as knock resistance with this mix versus the 20% mix. So this basically confirms what "cbrtx" said above, keep it at 20% or so and get the benefits with the least amount of fuel trim adjustment.

Fuel trims are about +10% with the 30% mix versus around +7-8% with the 20%, both of which are what I expected.

LMMFAO

 

[KrisR]

Dyno from Dynojet mobile dyno at Car Craft Summer Nationals today. This is stock except for the Airaid intake / Bama 93R tune combo and JBA mufflers which probably don't really do anything. This is 3rd gear in my automatic car (I have seen 4th gear pulls make 5-10 more hp and tq but take a custom tune to hold the trans in 4th gear). This is a 20% E85 / 80% 91 gas mix. The air fuel plot looks a little leaner than ideal but I don't put much faith in tailpipe sniffers as they seem to vary, but typically the ones I've experienced read around .5 leaner than a typical in-car / screw in wideband sensor.

I was expecting around 355-360whp but was pleasantly surprised.

 

[MikeT]

are you keeping the mix at 80/20 on every fill up now?

 

[KrisR]

are you keeping the mix at 80/20 on every fill up now?

Somewhere around there usually. Wife and I went on a roadtrip last weekend and I filled up with 91 gas twice just for highway cruising. But typically I put in a similar mix.

 

[MikeT]

Just wondered if worry at all about that mix, say, if you were on strait 91, then did the mix on the next fill up, and immediately beat on the car, like, leaving the gas station? would you be worried, or does the car adjust immidiately

 

[KrisR]

Just wondered if worry at all about that mix, say, if you were on strait 91, then did the mix on the next fill up, and immediately beat on the car, like, leaving the gas station? would you be worried, or does the car adjust immidiately

Well it takes a few minutes for the change in fuel to go through the fuel system anyway, so it's not like you immediately have a big change in the ethanol percent. I probably wouldn't go out and do a Texas Mile-style pull right away. I usually do a couple short wot pulls to get the short term fuel trims to let the computer learn a little if need be and then according to my datalogs it's good to go.

 

[DTL]

Im curious if the fuel trim percentages would be more dramatic on a power-adder car? I'd always thought that doing this (mixing) would make the car run lean anyhow, due to the different stioch. between gasoling and E85, but now that testing seems to show this working, I'm thinking about it again!!

 

[KrisR]

Im curious if the fuel trim percentages would be more dramatic on a power-adder car? I'd always thought that doing this (mixing) would make the car run lean anyhow, due to the different stioch. between gasoling and E85, but now that testing seems to show this working, I'm thinking about it again!!

I don't know that the percentages would change much on a power adder car vs an N/A car. I, for one, would be super careful and very diligent on datalogging, at least after the initial fill-up with each tank. I would try a very small amount first (maybe 3 gallons in the tank, less than 20%). You should see fuel trims that are around +5% of what they normally are with your 'regular' fuel (if LTFT hasn't learned fully yet, add LTFT and STFT together and they should equal around +5% or 1.05). Many of my datalogs at WOT have around 1.03 STFT and 1.03 LTFT because I spend so little time at WOT that the long term hasn't fully learned the 6% or whatever yet so it's relying on short term for a small correction also.

Also make sure you have lots of 'headroom' with your fuel system as this will require more fuel obviously. If you are close to being out of pump/injector, do not do this. Obviously you can datalog fuel pump duty cycle....not sure on injector duty cycle or similar? I haven't played with that yet.

I would say that if it were my car and I knew I had enough fuel system headroom, I would play with it a little bit. I can't say a blanket statement like 'everyone should do this always' because I have not tested it THAT much and obviously I am naturally aspirated, so the tuning window is a little wider as far as safety goes. Theoretically though it should help blower cars most, especially positive displacement blowers that make a lot of heat. Or, if all you have is a 93 tune and you are stuck somewhere that has only 91 octane but also has an e85 pump, like many gas stations in my area.

Try it at your own risk. I'm not going to say, "yes, do it, it will be awesoooooome" because I would hate for something negative to happen to someone else's car. These are just my experiences, with my nearly stock car, so far.

 

[gizmo5]

Just pour in some vodka and call it a day! lol

Sent from your moms room...

 

[Seer]

Just pour in some vodka and call it a day! lol

Sent from your moms room...

sugar content in vodka... would not be a good idea.

 

[gizmo5]

sugar content in vodka... would not be a good idea.

I was joking.....

 

[Seer]

I was joking.....

I know...but some people are dumb, may actually follow your advice on that one LOL.

 

[tbrock]

Tried two gallons of E85 with 91 on my saleen sc'd car. Gas mileage fell by 4mpgs for the tank, but the car responded well. The car seemed to respond similarly to how it does when I throw some race gas in. I know it is purely anecdotal evidence. I'll do it again and run a datalog to get better data.

 

[s8v4o]

sugar content in vodka... would not be a good idea.

Vodka doesn't have sugar in it. The reason why vodka won't work is because they mix it with water to achieve 80-90 proof (40-45% alcohol). When the vodka comes out of the reflux still it is usually around 190 proof, or 95% alcohol by volume. That will work perfectly fine for a vehicle ready for ethanol.

 

[KrisR]

Tried two gallons of E85 with 91 on my saleen sc'd car. Gas mileage fell by 4mpgs for the tank, but the car responded well. The car seemed to respond similarly to how it does when I throw some race gas in. I know it is purely anecdotal evidence. I'll do it again and run a datalog to get better data.

If you aren't self-tuning, with a car like yours (pre 2011) I would be leery of doing this, because as you probably know the older S197s run in open loop at WOT, so no fuel corrections can be made via the 02 sensors at full throttle. In Closed loop (cruise/idle/light accel/etc) the fuel trims will take care of it. At WOT with 2 gallons of E85 you are running about 3-4% leaner, so if your old air/fuel ratio (with no E85) was 12.0:1, you will now be running at about 12.5:1 if you didn't do any fuel correction in the tune. Granted the extra octane/cooler burn will help stave off detonation but I would certainly keep a close eye on it. If the car was tuned extra-safe for pump gas anyway (say 11.0:1) the tune will still be in the safe range (mid-11s) with a 2-gallon mix.

 

[tbrock]

Thanks for the info as I am seeing 11.4-11.5 at WOT on both my street and race tune. So I had a little extra room to give it a try. My previous tune was at 11.8 which could have been trouble.