XFI Lambda and AFR for E-85

[NY Twin Turbo]

I always thought I was clear on this. But I feel I have to double up on the info.

When XFI gives you the current AF number as read from it's wide band, it only gives you AF as most people know it to be with gasoline. Correct? So it converts the Lambda number into an AF number for the average dumby who has no idea that a perfect burn is not always with gasoline and that means it's not always 14.7 to 1. In actuality, it doesn't make a calculation based on the physical amount of fuel being introduced into the calculated air mass. Right?

What I'm getting at is this...... If I put my fuel energy constant at .680, and leave my AF map alone, and add true and tested E-85 to an empty tank.........why can't I tune using the old AF numbers for rich/lean reference, since this is what I'm used to doing? Lambda is what the computer really sees anyway. Now all I should have to do is add 3 or 4 degrees of timing globally to the entire spark table. No?

If I used to run an 11.4 AF (also known as Lambda .78) at 20 psi and now I change the FEC to .680, I should still leave the AF at 11.4. This will still give me Lambda .78. Because if I change the AF to 7.6 I'll drown the motor and it won't be at Lambda .78. And this is the real number I'm looking for.

I understand there may be a bit more to the actual tuning. Maybe warm-up, cranking and starting, ect.... But, all things being equal (except for timing) nothing should change. I easily have the fuel system for it.

Of course I can just use the XFI in lambda mode, but since I'm more familiar with AF numbers why can't I just keep using it this way.

Am I way off here. Or is it nearly this simple.

 

[pacecarta]

target 7.6 at 240kpa / 7.2 @ 280kpa

 

[NY Twin Turbo]

target 7.6 at 240kpa / 7.2 @ 280kpa

Thanks Paul, but I think you missed my point. The real question is, if the target is 7.6 @ 240kpa with E-85 (which is the same as Lambda .78) why can't I leave the AF at 11.4 (which is also Lambda .78) as if I was using gasoline? What does it matter if the AF is changed on the map? Doesn't the XFI use the Lambda equivalent as being .78 anyway?

By changing the FEC number to .680, I'm already asking the computer to globally add about 35 percent more fueling to the entire tune. The computer only knows a richer or leaner burn based on how much oxygen is left over. 11.4 AFR could be used spraying grape juice into the motor as long as the equivalent number it's really using to make corrections is Lambda .78. No?

 

[pacecarta]

make sure lambda mode is not checked

 

[NY Twin Turbo]

make sure lambda mode is not checked

Why does this even matter? All that does is show it in the way it really always sees it anyway. The AF mode is just for most of us dummies who don't know what Lambda really means. So, no matter what mode your in, as long as the FEC is set properly (which adds the appropriate percentage of additional fuel based on fuel type) it's still going to achieve what ever Lambda is called for on the table.

So, am I crazy? Or are all the guys who talk about E-85 AF's wasting their time? All you need to do is change the FEC and your there.......aside from some small open loop start-up parameters, of course.

 

[pacecarta]

try it at 11.4 and let me know how that works out for you

 

[NY Twin Turbo]

try it at 11.4 and let me know how that works out for you

Thank's Paul, but I'm more interested in theory at this point. And I was hoping for a little more input before melting a very, very expensive motor. Especially from someone as vociferous as you normally are on other matters. But since you may be the only person who actually would remotely entertain this discussion....I guess I'll take what I can get.

I'm also interested in knowing what Lambda numbers people see XFI when they run their motors at AF's richer then 9 to 1 on E-85. Because if they are the same as with gasoline, then they must have had to severely tweeked their VE map to death.

 

[pacecarta]

e85 ve table doesnt look much different from any other
af table has to follow whats needed for e85 ethanol

 

[NY Twin Turbo]

e85 ve table doesnt look much different from any other
af table has to follow whats needed for e85 ethanol

Even if the FEC is changed?

 

[pacecarta]

ill show you the table but i wont post it

 

[NY Twin Turbo]

Then why have a FEC option box at all?

 

[NY Twin Turbo]

ill show you the table but i wont post it

My brain hurts........I'm going to sleep.

 

[pacecarta]

you have an FEC so you dont have to screw the ve table up

 

[northerngn]

fec box checked and my car loved 7.9:1 afr under high boost on E-85

 

[Eric Stage I]

When XFI gives you the current AF number as read from it's wide band, it only gives you AF as most people know it to be with gasoline. Correct?

No, not if you change the fuel energy constant. It will rescale the AF for whatever number you use for the constant. If you change your FEC to .68, your target AF map will automatically change to the rescaled numbers.

If you would rather think in terms of gas AFR, you could leave the FEC alone, and reduce the injector size parameter by about 30%. This is how we make a classic fast work with E85, which doesn't have the FEC setting.

Eric

 

[NY Twin Turbo]

No, not if you change the fuel energy constant. It will rescale the AF for whatever number you use for the constant. If you change your FEC to .68, your target AF map will automatically change to the rescaled numbers.

If you would rather think in terms of gas AFR, you could leave the FEC alone, and reduce the injector size parameter by about 30%. This is how we make a classic fast work with E85, which doesn't have the FEC setting.

Eric

Now that makes perfect sense to me! I never actualy changed the FEC number! Not even once to try it of-line on a saved tune! Now it is sooooo clear to me. Eric, you are the best! You just so simply solved my confusion.

OK. So the Lambda does stay the same. The AF will change it's self when you change fuels (FEC).

So, it theory, if your current AF and your VE map with gasoline is spot on, which also means your lambda is spot on, all you have to do is stick with the new E-85 AF table as provided by the XFI and you should be good to go? No?

In the real world we know some minor tweaking needs to happen. As always, this most certainly will be the case. But.......In theory.....

 

[bison]

No, not if you change the fuel energy constant. It will rescale the AF for whatever number you use for the constant. If you change your FEC to .68, your target AF map will automatically change to the rescaled numbers.

If you would rather think in terms of gas AFR, you could leave the FEC alone, and reduce the injector size parameter by about 30%. This is how we make a classic fast work with E85, which doesn't have the FEC setting.

Eric

The ve numbers can only be increased so much before they are at max. 120iirc. Running the correct FEC for the fuel being burned is the way to go for sure


Sent from my iPhone using Tapatalk

 

[Eric Stage I]

When you reduce the injector size by 30%, it increases fueling by 30%, so no need increase VE (beyond normal tuning).

I agree though, using the FEC is the more correct way since the AFR will display correctly.