Stock 2008 Corvette Flex Fuel Conversion

[iced98lx]

Hi all, 100% noob here so please do assume the worst . I've read up a bit here and there and have some understanding of the basics (Virtual VE excluded) on how the e38 ECU is handling the motor. I've just received Dedicated Motorsports Flex Fuel kit (Thanks Dave, super nice bit of kit!) and will be taking off on installing it over the weekend. In the mean time I'm piecing together what needs to be done tune wise to support flex fuel. I'm clearly not too concerned about 'maximizing' the timing gains since the car is 100% stock otherwise at this point. (Headers are in the garage waiting to go on next, august timeline for a heartbeat blower).

Being a noob I'm reading this guide: http://www.g8board.com/forums/115-in...uel-setup.html as it touches on the tables not filled in for the G8, and using it as a sort of reference for my C6. I've checked the basic boxes (see tune attached) but wondering if anyone had any suggestions vs the holden 6.0 tables for the Engine>Spark>Advance>Spark Correction>Flex Fuel Spark table? As I understand it the others listed (Engine>Fuel>Transient>Transient Fuel Mass Evaporation>Evaporation Factor Blend / Engine>Fuel>Transient>Transient Fuel Mass gain>Impact Factor Blend) are simply telling the computer how to land in between the Gas and Alcohol tables (both of which already had data in them) if it isn't either 0% or 100% and so the tables being from a 6.0 LS2 shouldn't matter there (Plus they're easy enough that I understand them).

I know the Flex Fuel Spark table is a bit of a secret sauce for those making big power on ethanol, but for a stock car I just want to make sure until I understand how to adjust it the best I can I'm not putting values in that are completely out of left field.

The other table that wasn't specified that I copied over from the 6.0 holden file was the Engine>Spark>Spark Correction>AFR Correction (Alcohol) table.

I noticed the "Alcohol Adder" table in the same area is blank in both.


Any pointing in the right direction is much appreciated, I will of course report back on how the sensor install goes and how it runs with various amounts of alcohol content...

TL/DR - Putting Flex Fuel sensor in stock 2008 here is what I touched vs stock, am I missing anything and do you have an opinion on the flex fuel timing table:

[BigMike42]

Here is mine, I didn't add any timing but I set up the multiplier so if I want to add some timing, it will work.

I just followed the g8 board recommendation and copied the 2012 holden files.

I zero'd out both gas and alc AFR adder tables for spark. Then I set my gas and alcohol PE ratio to the same thing and I set the Mult vs Composition table to all 0s up to 50, then all 1s from 50 to 100.

Then you can leverage the flex fuel spark table and add spark wherever you want and it will get multiplied by whatever you set in the mult vs comp table. Flex fuel spark is just an adder, not like the main spark table.


g8-idle-best.hpt

[BigMike42]

Shit I almost forgot...

In the beta and 3.0, I could not find the sensor diagnostic enable setting. I had to use the old 2.24 software to flash it in.

diag.png

[schpenxel]

If you're missing anything like that in V3 email support

[iced98lx]

Thanks Mike, I noticed the same thing RE: sensor diagnostic setting and will open a support ticket in case they're not aware.

I understand zero'ing the AFR Adder tables so nothing else is altering spark (right?) but for stock I don't see why I'd not leave them alone? I don't understand when the spark correction tables kick in (PE, right?) so I guess outside of trying to simplify I don't see a reason to zero them.

Setting the Mult vs Comp table under spark correction I missed, thank you I have set that table up.

Leaving the Flex Fuel Spark table at zero's I guess simply won't do any correction timing wise for what alcohol prefers, which likely won't "Hurt" anything but isn't "optimal" (this is where the secret sauce part comes in I guess). I'm going average the holden 6.0 and the silverado 6.2 stock tables as a starting point for this table I think...

[BigMike42]

Sorry, confused by your question, so I edited post.

Spark correction is PE and COT only. I would just leave them zero'd forever.

Use the flex fuel spark table for all your spark changes since it's constantly enabled and based on rpm and airmass only (no confusion)

Tune the car like it's on gas and then just slowly add spark using the one spark table. Without a dyno or a way to compare results, it's pointless to even start adding any though.

[BigMike42]

Also, if you're N/A you'll likely have the same WOT spark as 93 unless your compression is insanely high. MBT spark is most likely the same for both fuels, so don't ge nuts unless you're on the dyno and you can measure differences. The HP gains in N/A cars are from the cooling effect mostly. Boost cars pick up huge because they can safely move the spark up to a more optimal setting.

[iced98lx]

Sorry, confused by your question, so I edited post.

Spark correction is PE and COT only. I would just leave them zero'd forever.

Use the flex fuel spark table for all your spark changes since it's constantly enabled and based on rpm and airmass only (no confusion)

Tune the car like it's on gas and then just slowly add spark using the one spark table. Without a dyno or a way to compare results, it's pointless to even start adding any though.

Thanks Mike, This is basically how I understood it, and I understand "pointless to add" as "Maximum add before detonation" isn't "Maximum horsepower"

What is interesting to me is that in stock GM tunes they use the Flex Fuel Spark table with both positives and negatives, meaning, they're adding timing and removing it at various RPM vs airmass areas. I do not understand when one would pull advance (retard timing, correct?) with e85, and wonder what sort of drive-ability gains they may be getting. I am going to try to see if there is a trend across various stock flex fuel tables as to when they are advancing and retarding timing for alcohol.

[BigMike42]

I noticed today after filling up that the new ethanol percentage doesn't register until I actually drive for a bit. I think it's the delay and transition volume settings. I wonder if it's safe to lower these, but I'm not 100% sure.

[schpenxel]

You can log "fuel composition sensor" frequency also--I think that one will react faster but could be wrong. Whatever the frequency is, subtract 50 and that's the alcohol %.

Name may be a little different depending on ECM/OS

Where's the sensor at in the system and what are the delays setup to now?

[BigMike42]

I stuck my sensor on the fuel line by the manifold.

I just used the stock holden values, .18L and .25L. I think I'll cut em and half and see.

[schpenxel]

Yeah, might could watch fuel trims right after putting in some E85 to see how they react, might give you some insight on whether to move these up or down at least

[iced98lx]

Mike/Schpenxel - I too was eyeing up those values. Seems to me that that is the time/flow the ECU waits to move after the sensor detects a change, correct? We should be able to turn that way down for cars where the sensor is practically on the fuel rail like the DSX kit since it won't really need to have a huge delay / volume before that fuel it's measuring is in the motor... I agree that the 02's should help clue in if it's early/late.

[BigMike42]

Mike/Schpenxel - I too was eyeing up those values. Seems to me that that is the time/flow the ECU waits to move after the sensor detects a change, correct? We should be able to turn that way down for cars where the sensor is practically on the fuel rail like the DSX kit since it won't really need to have a huge delay / volume before that fuel it's measuring is in the motor... I agree that the 02's should help clue in if it's early/late.

Is it in reference to after the sensor detects the value? If so, we can basically just make them close to 0. All we'd have to account for is the amount of fuel in the fuel rail plus a little extra. Anyone know this value? I suppose it would be easy to calculate.

[schpenxel]

Yes, it's basically saying once there's a change in ethanol content at the sensor, how long does it take for the new ethanol % fuel to make it to the engine.

Makes more sense if the sensor is close to the tank and you have a good bit of fuel between it and the engine

For the sensor right at the rail you should be able to set those values quite low

[iced98lx]

they appear to be compounding values, if the tool tips are to be believed. I assume this is post-sensor only because how else would the ECU know about the change

Delay Volume- [ECM] 3147 - Composition Change Delay Volume: Volume of fuel required to be used by the engine before new composition reaches the engine.


I am assuming the "New Composition" is what the sensor is detecting?


Transition Volume - [ECM] 3148 - Composition Change Transition Volume: Volume of fuel used by the engine during a fuel composition transition, after the delay volume is used.

So it seems after the delay volume it attempts to "Blend" for this amount? I'm not sure what the implication is but I'd guess it's not obeying the basic Flex Fuel timing tables/rules until after this volume, or at least is slowly transitioning?

[schpenxel]

If you're starting at 0% ethanol and going to 50%

Say delay volume is 0.1L and transition volume is 0.2L

For 0 to 0.1L used ethanol % will stay at 0%. This is time it takes for beginning of new fuel to get to rail

For next 0 to 0.2L used it will transition from 0% to 50% "ethanol" content. This is time a mix of old fuel/new fuel is going through rail. Transitions to whatever flex fuel sensor value over 0.2L in this example.

You should be able to log these easy enough and see it in action

Regardless, with a sensor right at the rail they're going to both be close to 0

[iced98lx]

That is how I understood it after reading, thank you for confirming. Like you said, a tiny amount between the sensor and the injectors in my setup so I'll set that very low.

[sevinn]

For those values on mine, I calculated the volume of the fuel line, fuel filter and estimated the volume of the fuel rail and set that to the delay volume, then I used the same ratio as the stock file I was copying to determine the transition volume. My fuel trims are pretty good after large ethanol percent swing using this setup so I'm fairly confident that's the right way to go. I'm only ever nervous about going from a high ethanol percent to a low one, but I'm not adding a crazy amount of timing and haven't desensitized my knock sensors other than disabling burst knock anyway.

[iced98lx]

Sevinn- what volume did you come up with for the fuel rail if you don't mind me asking? That'd be about the volume I'm working with.