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L83 5.3L Flex fuel conversion with Dyno sheets. Followed with tune and more dyno sheets.


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43 minutes ago, truckguy82 said:

I’ve never driven a car with e85, they dont offer it in my area.

 

but I would think the e85 changes ignition and fuel timing. I would think that would give you a boost in the low end too. Maybe it only changes the open loop tables? But that doesn’t make that much sense either.

 

hmm

 

Meh....not that I noticed. Maybe I would have it I was matting it at every stop sign and signal light. But I accelerate at the same pace regardless of the fuel. So I expect that IF there were some life altering feeling of power I'd have just pushed the pedal 2% less and gone about my merry .25 G pull up to speed. People forget than alky has allot less heat content than gasoline and because of that requires allot more of it;  but the number of oxygen atoms in the air is unaffected. A .25 g acceleration rate takes the same amount of power no matter what fuel is loaded. Force is dependent on mass once rate is established. You have to ask of the fuel, given the same mass, a greater rate of acceleration than the base fuel can supply to GET THE DIFFERENCE it may supply. I don't drive like that on city streets. Save that for the track and I haven't been there in years. That's just physics. I can do nothing about people perceptions. 

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1 hour ago, Alec Kerchner said:

Yeah, the grunt off the line and throttle response is like driving a different vehicle. It's amazing how different it is just by switching fuels. 

My 14 GMC had flex fuel. Did I notice the 25HP yes. The throttle response was better, less input needed. I also had a can tune. Usually I would check the box for the premium tune I didn’t. I did the usual increase shift points and RPM increase and 50 percent TM. What a difference. What I like the best was on trips back to reg gas. Do I burn rubber at every light? No. I like knowing that it’s there if I’m feeling the mood. It’s wasn’t all about  fuel mileage to me. 

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It's really quite simple - @Grumpy Bear doesn't get deep enough into the load range to notice the difference that the extra ignition advance adds. Here's a paste of a stock Flex Fuel timing table. This adds (or subtracts) based on another multiplier which references alcohol content. 

 

image.thumb.png.d318668eae40dfa7a202a7c10ca52a36.png

 

Something else worth mentioning is knock learn factor. Allow me to explain. If you've been running 87 then your ECM will have certainly "learned" to run less ignition timing because it detects knock at higher loads at various RPMs. Basically, if the ECM detects greater than 3* (on my L86) of knock then it will interpolate between the high and low octane spark table to find a value that doesn't knock. If you randomly fill up with premium then it will slowly realize that there isn't any knock present and start learning back to the high octane table. 

 

Why do I bring that up? If you run ethanol for several consecutive tanks you are allowing the ECM to bring back ALL the ignition timing that it's been removing (assuming 87 octane) PLUS it will be adding more timing in the higher load ranges. This extra timing should make a big difference in the way it feels in top gear lugging around. 

Edited by lucas287
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14 minutes ago, lucas287 said:

It's really quite simple - @Grumpy Bear doesn't get deep enough into the load range to notice the difference that the extra ignition advance adds. Here's a paste of a stock Flex Fuel timing table. This adds (or subtracts) based on another multiplier which references alcohol content. 

 

image.thumb.png.d318668eae40dfa7a202a7c10ca52a36.png

 

Something else worth mentioning is knock learn factor. Allow me to explain. If you've been running 87 then your ECM will have certainly "learned" to run less ignition timing because it detects knock at higher loads at various RPMs. Basically, if the ECM detects greater than 3* (on my L86) of knock then it will interpolate between the high and low octane spark table to find a value that doesn't knock. If you randomly fill up with premium then it will slowly realize that there isn't any knock present and start learning back to the high octane table. 

 

Why do I bring that up? If you run ethanol for several consecutive tanks you are allowing the ECM to bring back ALL the ignition timing that it's been removing (assuming 87 octane) PLUS it will be adding more timing in the higher load ranges. This extra timing should make a big difference in the way it feels in top gear lugging around. 

i’d assume the maps instantly change when the sensor detects e85.

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8 minutes ago, truckguy82 said:

i’d assume the maps instantly change when the sensor detects e85.

 

For all intents and purposes - yes. The alcohol sensor will immediately report composition changes exceeding 2% to the ECM. Then, there's a delay based on volume (.28 liters for my truck). Basically, it wants to use all the fuel from the sensor to the rail first BEFORE making changes. 

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7 minutes ago, lucas287 said:

 

For all intents and purposes - yes. The alcohol sensor will immediately report composition changes exceeding 2% to the ECM. Then, there's a delay based on volume (.28 liters for my truck). Basically, it wants to use all the fuel from the sensor to the rail first BEFORE making changes. 

Wouldn’t that negate your post about learning via knock sensor?

 

i mean it’s changing to a different map, I’d assume it’d have to relearn.

 

also I though the learning process was much much faster than a few tanks. i can’t verify this, just what I’ve heard

Edited by truckguy82
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10 minutes ago, truckguy82 said:

Wouldn’t that negate your post about learning via knock sensor?

 

i mean it’s changing to a different map, I’d assume it’d have to relearn.

 

also I though the learning process was much much faster than a few tanks. i can’t verify this, just what I’ve heard

 

Nope. The flex fuel table only adds (or subtracts) from the current "learned" amount of timing it's running. While I don't fully understand how "knock learn down" function works the values prepopulated in HPTuners looks like it would take a hot minute.  

Edited by lucas287
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Knock learn factor is simple. The KLF starts at 1 or 0 depending on the PCM used and year range and they go to 0 or 1.

 

Say it starts at 1 and goes down to 0. The 1 would be the high octane table current timing number, lets say 25 degrees. It detects some knock and slowly works it way toward 0 on the KLF and lets say it stops at .50. If the low octane timing table had 19 degrees in the same area of the timing curve it would pick 22 degrees of timing.

 

The knock learn factor doesn't even need to wait for a new fuel to work it's way back to "1" on the KLF, it just doesn't have to show knock for a long enough period of time to make it from .50 back to 1. You should be able to watch the KLF in the HP Tuners scanner to see it working. I partly think that once it knows it's been showing a decent amount of knock everytime the go pedal is pushed hard enough, the predictive knock function of the calibration called burst knock starts to play a larger roll in how much timing it quickly yanks away before any actual knock is detected. Then once a better fuel is ran for long enough it slowly weens that off because it's not showing as much or any knock anymore.

Edited by CamGTP
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