I've been looking at going to EFI for a while. I was originally looking at the new Holley HSR systems with their new HP ecu. But since I am now getting closer to making the swap a reality, the recent rising in gas prices has got me leaning towards putting together a system that is flex fuel compatible. It would be really appealing to be able to run a 105 octane fuel from the pump for 60 cents less than premium and many dollars less than racing fuel. Now I know some will debate running E85, but this post is not an argument for or against. I've decided I want to make this happen and since I'm swapping in a LS1 tank and running new fuel lines, there will be no problem making it E85 compatible (stainless lines, teflon lined fuel lines, new fuel regulator, injectors) and using a Racetronix pump with the tank, I should be able to supply the extra 47% of fuel required to run E85 (only planning maybe 450hp at crank).

I really like all of the controllability options with the HP ecu, but it lacks flex fuel sensor compatibility. Now I know I could make 2 different tables and swap tables depending on what I wanted to run at the time, but I would really like to make this true flex fuel where I can run any mixture between E10 gas and E85. The only ECU's I have found that support the GM flex fuel sensor are FAST XFI, BigStuff3, Megasquirt, and ProEFI. Can anyone give me particular experience with any of these ECU's, specifically if you have used the flex fuel sensor with them?

I really like the FAST XFI, but from what I've read, it doesn't actually change the fuel tables based on the ethanol content. So if you programmed the ECU on gas, it just uses a mutiplication constant (based on the fuel constant calculated from the sensor input) to add excess fuel on top of the gas table to maintain an equivalent lambda. This means that you can only really have optimum power on one fuel with the other fuel being a compromise since the maximum power of gas may be at a richer lambda than required on E85 (read this in a few articles and I believe a table in the Megasquirt Megamanual lists these lambda values). It also means that the timing does not change between the gas and E85 tables meaning that not as much power can be made since on E85 the engine can be advanced a good bit more. What I'm looking for is an ECU that you can basically tweak the gasoline and E85 fuel and spark table parameters separately and then the ECU uses the input from the flex fuel sensor to basically interpolate between these two graphs. Does this exist in any ECU (even ones I haven't listed)? I believe the Megasquirt and BigStuff3 both do this, but I'm not sure.

Does anyone have any experience with this? Any input would be greatly appreciated.

I'm also looking for input on which manifold to use. Since I'm probably pieceing a system together, I'm up for opinions on manifold usage. I know this section isn't for manifold opinions, but I'm looking for opinions between the HSR and the Edelbrock intake. I'm really starting to lean toward liking the Edelbrock intake and the way it looks more so than the HSR, but I've only ever seen good dyno data to support the HSR. Anyone have good experience with the Edelbrock intake? This will be going on new 383 I'm building for my car, with the same top end as 350 thats listed in my sig.

 

hmm... i was actually considering patching in the ability to to at least read estimated alcohol content in the fuel via a sensor using a 7730/7727 with $A1...

then use that reading to determine the fuel's stoich AFR and potentially a static PE AFR(or a multiplier), but spark changes might be more difficult... or at least more time consuming.

i was thinking two sets of main spark tables, one for pure gasoline(or at least as close as possible), then one for pure alcohol(again, as close as possible), do 3D lookups for both, then use the alcohol sensor's data to interpolate the results.

but that seems like it would take a lot of CPU cycles... and then there's also the issue of having fuel that has a higher ethanol content without a lot of octane, like the E10 87 octane fuel that's so common.

just thoughts, anyways.

 

Has the cost of the sensors come down? I looked into doing this a few years back but the flex-fuel EOTH sensors were in the $600 range.

At the same time GM moved away from using the sensors and letting the ECM adjust via the fuel trims.

RBob.

 

What kind of mpg can you get out of E85? From what I hear, an E85 engine roughly consumes double the fuel. It would be like turning 200 miles per tank into 100 miles per tank.

 

it's not double, but it is increased fuel usage...

for comparison, check out http://www.fueleconomy.gov/feg/sbs.htm and find a vehicle you know does E85. i chose an 08 impala since they're everywhere and i know there are 3.5 and 3.9 motors that can run E85.

on E85, it's 13/20
gasoline: 18/28

for the 3.9

 

Saar, I had never though of using a stock ECU and reporgraming to interpret. I haven't done to much research on stock ECU's since I never wanted to have to burn proms, etc. What is that ECU for and is flashable? I also will admit I dont' know a whole lot about the programing within an ECU... I just know that the bin is different for each differnet model ECU and that it is the "map" the computer uses. But it would be cool if you could find a way to use a stock ECU, although I'm still leaning towards using an aftermarket anyway.

I'm not really concerned with worrying about runnign regular unleaded (although some might) since I'm planning on having 10.5:1 compression, so premium is a must anyway. What you are talking about pertaining to the fuel and spark tables is basically what I'm looking for though. I'm looking for the ability to have a gas spark/fuel table and E85 spark/fuel table and be able to interpolate between the two based on the input from the sensor. This would allow tuning separately for E85 and pure gas, being able to get the most out of either. I will agree that this seems like it would require a lot of processing power, especially if the refresh rate is high. I also don't know how much memory the stock ECU's have so would all the information be able to be fitted into a bin file that could be saved in memory?

As far as the GM flex fuel sensor goes, they are still about $600 new, but go for about $150 on ebay for used ones, so I felt this would be sufficient. I do know that if you buy the BigStuff3, you can buy a complete add on flex fuel kit with sensor for $1000.

I had read about ECU's that didn't use a sensor, but I thought it was older ones and not the new ones (I'm not sure so I'm asking). How does this work in the ECU to be able to do this without have ethanol content input?

As for fuel economy, I've read that its about a 25% to 30% reduction in fuel economy. But E85 has the potential to make more power, helps the engine to run cooler during the summer months, and is just different. From most I've read about performance applications, it is cheaper per mile to run E85 even with the reduction in fuel economy. Usually the tuning will come into effect with the fuel economy, though, since not having cats, or needing to meet emissions, I can run leaner during cruise on both fuels than oem cars do.

 

it's certainly possible on a 7727/7730, there's plenty of A/D ports left in any mask to read a single sensor. there's also plenty of space in the BIN to work in a patch, especially if you move to a 512 PROM, though at least in the A1 mask, there's plenty as-is. it may be possible to offload some processing power by running multiplier tables for spark control, basically take the gasoline tables and add spark based on the alcohol content... that would actually be a lot quicker and require less PROM space.

 

Spark added to the gas table based on sensor input would probably work just fine since that's really all you're trying to achieve. I don't know a whole lot ab any stock ecu so I can't give any input on the programming for that but it definately sounds like you're thinking in the same direction as what I'm wanting to achieve. The only thing that I like ab the aftermarket route, however, is that just ab all are sequential injection. This would definately help out with idle and cruise ranges on the gas side of things since the injectors would have to be ab 60# ones to be able to support my anticipated power goals on E85. At least then when I'm running on just gas there would be a lil more control over each individual injector and I could possibly size the injectors smaller than that since each would have longer to fire per combustion cycle.

This is some really good information you're providing though saar. Definately food for thought for some who may want a lower budget way of implementing this kind of setup or already have the tools necessary to tune proms. But does anyone else have any experience w the flex fuel sensor w any of the aftermarket ecus and/or know if any of them will accomplish what I've stated I'd like the system to do?