Hey All, Odd question I was hoping to get clarity/guidance on from you all. Essentially I want to disable duel fuel, move all my secondary/alt tables to primary, and multiply my new VE table 1 by 1.63 in preparation for a fresh single fuel (E85) tune this weekend.

My 400hp EFR turbo car was originally tuned (2 years ago) as Dual fuel Enable- ON. Flex Blend, Using E10 and E85 as my two tables with a blend curve setup. I was told by the tuner i needed to keep the car in a sweet spot of above e64 but below 70 as to not over boost. Which has been annoying and never really made sense to me. But was told.. yada yada limitations of mega squirt and flex fuel.

Fast forward to today, and the car is setup with a ZF6 transmission, ign1a coils and I want the car to make power sooner and hold it for track only use of e85. Not chasing peak power anymore.

Current Tune info-
Dual table enabled for Fuel/spark alt overboost, alt boost, and alt accel enrich.Flex sensor settings of the below. Basically is multiplying VE table 3 by 63%..

 

You don't gain anything by disabling the dual fuel system as far as ignition and fuel is concerned. MS3 does a linear interpolation between 0 and 100% ethanol and uses between 0 and 163% multiplier depending on the ethanol content on top of interpolating between the tables, and it does the same for spark. It works quite well like that. If you already have a flex sensor, I suggest you use it.

If you must only have one fuel and ignition table, the correct way to go about it is to change the REQ_FUEL in the Engine and Sequential settings. Use the stoichiometric ratio of e85 to calculate a new REQ_FUEL, and move your VE3 to VE1 when you disable the dual fuel system. You should then retune VE1. Also make sure to go on General Settings and set the stoich ratio to 14.7 to keep your AFR Target table making sense. The issue is if you even go to e70, instead of e85 you'll be at the mercy of a good EGO correction to keep the engine happy.

My 4 cents is that you leave flex fuel on and have that tuned. You could have your tuner set it up boost control as closed-loop with one of two options
- A switch you can toggle between two boost control tables, one low boost or wastegate, the other full beans
- Only one boost table that is full beans, and have the switch disconnect the boost controller, which will give you only wastegate pressure.

I like the switch idea on MS3 because it lacks a lot of correction tables for warmup and heatsoak so you can only tune for a limited set of conditions. I'm personally not a fan of the boost target interpolation based on ethanol.

 

Hmm, i think I am tracking but not fully. I appreciate the dialogue. I don't need to have one fuel and ignition table, that was my initial thought to simplify this. But yes i will always be somewhere around e70ish.. or so (whatever summer pump e85 is reading at in my area).

Linear interpretation between 0 and 163%- the blend table isn't linear on my tune. Not tracking this.

Your paragraph 2 confuses me all around but not your fault. Essentially you are saying req fuel should be calculated with E85 (70) as the norm? But keep the tables as 14.7 as stoich.
4 cents- I only want full beans.. its a track only car. i don't need and switch or alternate boost tables.
With Flex fuel still on, this can be done with only 1 table still correct? just the multiplication of the table is adjusted based on E%? Is that worth it if always expecting to be above E65ish or whatever?

 

There are two different mechanisms at play with FlexFuel in MS3. The first is the linear interpolation between 100% and 163%, where 10% ethanol adds no extra fuel, and 100% ethanol adds 63% extra fuel. It starts at 10% because of your ethanol base line, and under this baseline (if you ever use non-ethanol gas) as small fuel removal is done. This is the setting in your first screenshot. This is what gets you in the ballpark for FlexFuel.

The second mechanism is the interpolation between VE1 and VE3, and this one is controlled by the blend table in your second screenshot. 0 in the blend table uses VE1, and 100 uses VE3. Numbers in between interpolate between them and this is what does the fine tuning for FlexFuel. This same blend table controls the interpolation of spark and boost in your case, and also controls other Dual Fuel interpolations if enabled (accel enrichment, cranking, etc). It's rare to get the same % of ethanol even from the same pump through out the year, and that's why I suggest you keep this system.

Yes, that's correct about the required fuel and stoich. When you change the stoich ratio in General Settings it changes what the AFR table means. The AFR table in the code is really a lambda table. Lambda 1 is Stoich for all fuels, but stoich AFR is not the same for all fuels. Lambda 1 of gasoline is 14.7 AFR, while Lambda 1 of E85 is 9.8 AFR. For 99% of us, keeping with the gasoline scale makes more sense when talking AFRs, and that's why I suggest you return that value to 14.7. There is a large thread around here about this. I'll have to dig it up if you want to understand it more in detail. But overall I strongly suggest you don't do this method and just keep using the FlexFuel system.

If your end goal is full beans all the time then turn off the alternate boost and overboost, and only use the high boost table. With the current setting anything under E80 starts removing beans. I still recommend a switch to have a wastegate setting though. Shitty E85 exists, or maybe you get crappy weather one day and want less beans. But what I'm getting to is that you don't need to remove all of the FlexFuel to have high boost all the time.

 

Ok, was but also wasn't aware of the two mechanisms but that makes sense. And yes understand 10% as bottom and 100% ethanol as the top. So you need both mechanisms to have a functioning flex system? First mechanism is how much each table is multiplied by, and the second mechanism chooses how to blend the two tables.

Can you have a system that only uses the first mechanism with one table? Flex fuel but only worrying about varying ethanol in the 60-80 range?

I fully understand stoich and how widebands really read stoich but display AFR thread. I deep dove into that a long time ago. Really dont want to go this direction and sticking to flex makes sense.

Ok yeah i think im tracking with your end goal interpretation. Turning off Alt boost and overboost is done in the flex settings menu correct? Your idea is to only blend VE tables but not boost tables. but add a switch to go wastegate if desired? Prob wont add the switch but i get that point.


If im reading all of this correctly, take my current flex fuel tune to the dyno session, turning off ALT boost/overboost and making my full beans boost table the only one. This still leaves me in the position with having to tune two VE tables, if i know im only going to run as much ethanol as physically possible does this still make sense?

 

In my book you need both for proper flex fuel with minimal EGO Corrections. And only for clarification, the first mechanism doesn't multiply the tables, it multiplies the base pulsewidth. Similar end result, but we're a bunch of nerds here.

Yes, you got it. You seem to already have a decent E10 spark and VE map, why not leave them be? If anything it will let you run a decently safe spark map if you drop Ethanol a lot one day. You could disable the second VE map and only run the linear mulitplier. This is how MS2 flex works. If you know you'll always be around E70-85 it will work fairly well with EGO corrections, but in my experience won't be ideal if you go too far from the original fuel. As to where to enable/disable all of this, it should be in the Dual Fuel menu, in the dropdown where you found the blend curve (sorry, not at my laptop).

 

@redursidae recently explained this same thing to me, so cool to see it in writing here to help me absorb.

After seeing this for myself I agree with him. Really the main or "coarse" correction is in mechanism 1 (as described above), with fine tuning happening with mechanism two. Together you can get a pretty damn close map before EGO kicks in in both WOT and part throttle/cruise (where mechanism 2 really shines).

You could probably get away with only mechanism 1 and identical fuel maps for VE1 and VE2 though, it's just better to use both.

 

Hm not really tracking the last line.

If one wanted to have flex fuel but only work for different value of ethanol percentage does it make sense for VE table 1 to be E10? or E60? And VE3 be as close to E85 as possible?