Flex fuel sensor on 94 LT1 EE possible?

[Fastmax32168]

I think my title probably explains my question pretty well. When I built my 94 LT1 based 383 I had easy access to race gas, and I built it with 12.5 to 1 compression. Now that access has dried up and I have to back the timing off substantially in order to run it on 93 octane, leaving lots of power on the table. I have tried a snow methanol injection system with limited success in controlling the detonation. I do have an E85 station only a few miles from me, so I am wondering if it is possible to set up an EE based system to understand a flex fuel sensor so that I could convert over to running E85? Thanks.

[steveo]

reading the sensor is an easy thing
the hard part is you would want two timing tables and two stoich constants and blend between them
would require some serious assembly code
we haven't even figured out EE with two timing tables yet as thats a huge table and there's no free space for another one

[steveo]

of course if you ran only e85 you don't need a flex fuel sensor...

[Fastmax32168]

Steveo, Only running E85 would be my plan, however from everything I have researched the level of ethanol in E85 is not consistent, you can have 80% in one batch the gas station gets, and 65% in the next batch. No problem if you have a sensor that can read it and make the adjustment, but a problem if I need to tune it every time I get another tank of gas....or alcohol...or whatever.

[Pulse_GTO]

Thought of changing to an LS1 computer?

[Fastmax32168]

I have not investigated what it would take to change to an LS style ECM. I just thought of the whole E85 solution recently, up until now I have been considering changing to a head with a larger chamber, but converting to E85 seemed quite a bit easier and cheaper if it would work, and I did not know what sort of capability EE had or didnt have until today.

[LeMarky Dissod]

Steveo, Only running E85 would be my plan, however from everything I have researched the level of ethanol in E85 is not consistent, you can have 80% in one batch the gas station gets, and 65% in the next batch.
No problem if you have a sensor that can read it and make the adjustment, but a problem if I need to tune it every time I get another tank of gas ... or alcohol ... or whatever.This, exactly.
Even if you get lucky and tune for E50 (the minimum), that just means you need another tune for E83, then maybe another tune for E72, and another for E61 ...
A 12200411 pcm (or its close relative) with far better flex fuel capability built in would be an easier solution, at least in terms of tuning.

[Tom H]

Looking through the 1997 LT1 code, it seems that there is a provision for low octane gas. Changes all sorts of tables centered around knock retard. I have yet to determine just how the code detects low octane. I wonder why the earlier LT1s didn't have this code (?) May have been a change when OBDII came in.

-Tom

[steveo]

I wonder why the earlier LT1s didn't have this code (?) May have been a change when OBDII came in.

EE does have low octane compensation tables and logic as well. it's probably the same code.


I have yet to determine just how the code detects low octane.

the logic is likely the same as most low octane compensation systems, if there are a lot of knock events within a certain timeframe, then it adds in more low octane compensation. the attack/decay is tunable.

that isn't really going to help this guys ethanol situation since spark is the not the biggest concern. if you don't have consistent ethanol levels, the difference between 50% and 85% ethanol is massive with regards to AFR.

[Tom H]

Thanks for explaining this a bit better.



the logic is likely the same as most low octane compensation systems, if there are a lot of knock events within a certain time frame, then it adds in more low octane compensation. the attack/decay is tunable.

In the end does software come up with a binary: good gas/bad gas or a number representing the gas quality?



that isn't really going to help this guys ethanol situation since spark is the not the biggest concern. if you don't have consistent ethanol levels, the difference between 50% and 85% ethanol is massive with regards to AFR.

I looked through the air/fuel ratio code and can see quite a few modifiers...
- Over temperature
- Power enrich
- Cat protection
- Cranking
- Open loop
and so on. Seems like the stock PCM probably isn't flexible enough to handle the situation. In the later code the OBDII command mode $AE will let you directly control the air/fuel ratio. I am sure the ALDL has a similar mode to temporarily adjust things. Perhaps he could do a test and find out if by adjusting the air/fuel the car could be driven with both gasses. Perhaps do this before spending on new heads. Also wonder if a thicker head gasket might drop the compression enough to be a help.

-Tom

[Fastmax32168]

Tom, Thanks for the thought, but the car can be driven just fine right now. It is just not operation at optimum, and it obviously wouldn't be with a "compromise tune" designed to allow it to just "operate" on various mixes. The car drives fine on 93
octane I Just need to take about 5 degrees of timing out of it, and that costs quite a bit of power. I am sure it is still over the 400 RWHP mark, so in a 3000 lb package, its not boring. Going to a thicker head gasket would change the quench area for the worst, I am doubtful it would be enough, or do any good. It could easily change the detonation issue for the worse.

[Tom H]

Going to a thicker head gasket would change the quench area for the worst, I am doubtful it would be enough, or do any good. It could easily change the detonation issue for the worse.


I can't see how a thicker head gasket would change the quench area... volume yes but area? I guess the thinner the quench the higher the velocity/better mixing/more power.
Not sure I know enough to post on this thread, so I will watch with interest.

-Tom

[steveo]

In the end does software come up with a binary: good gas/bad gas or a number representing the gas quality?

i guess you could view it as a number representing gas quality. it's just part of an overall closed loop spark control system. you can think of regular knock retard kinda like short term trim and octane comp as long term trim if you want

if you have poor quality fuel and your timing map is too aggressive for it, it'll go into a cycle of knock, decay, knock, decay....so you're still getting lots of knock events spread out over time. low octane compensation tries to lengthen that cycle so there's less actual knock (by removing more spark from more critical areas, and having a longer decay time)

[steveo]

The car drives fine on 93
octane I Just need to take about 5 degrees of timing out of it, and that costs quite a bit of power. I am sure it is still over the 400 RWHP mark, so in a 3000 lb package, its not boring. Going to a thicker head gasket would change the quench area for the worst, I am doubtful it would be enough, or do any good. It could easily change the detonation issue for the worse.

it actually sounds like a good tuning challenge to me. you might be surprised what you can achieve on 93 octane if you don't just approach the problem as just dropping 5 degrees of timing. there is a delicate balance between AFR and timing advance that you can play with to get a lot of power back, and spark is really complex, some running areas might not need much help at all. you might have a lot of fun with it.


I can't see how a thicker head gasket would change the quench area... volume yes but area?

you're confusing deck clearance with quench, that's all. lots of people mix those up because even a lot of machinists seem to use the wrong terms and it gets passed around.

[Tom H]

you're confusing deck clearance with quench, that's all. lots of people mix those up because even a lot of machinists seem to use the wrong terms and it gets passed around.

Could you expand your answer and clear this up for me?

Thanks,
-Tom

[In-Tech]

If I am incorrect of what steveo is talking about, please advise.

Basically quench is the distance from the flat parts of the head to the piston. Let's say your engine is assembled with the piston .010" down from the deck(deck clearance). If you use a standard .038" thick gasket, you will have .048" quench. Most hot rod people try for .035" - .040" quench. The desired quench can be done with deck machining or gasket thickness.

[Fastmax32168]

Tom, The quench area is the tight area between the flat portion of the piston and the flat portion of the combustion chamber. Its purpose is to squeeze all of the mixture into the combustion area, so you want it as tight as possible without making contact. If you put a thicker head gasket in, then that area becomes less efficient, holds more mixture, and becomes more prone to detonation.

[NomakeWan]

Steveo, Only running E85 would be my plan, however from everything I have researched the level of ethanol in E85 is not consistent, you can have 80% in one batch the gas station gets, and 65% in the next batch. No problem if you have a sensor that can read it and make the adjustment, but a problem if I need to tune it every time I get another tank of gas....or alcohol...or whatever.

Where are you located? This is true in places with no regulation defining “E85.” In places like California that get their E85 from Pearson Fuels, however, your ethanol content is guaranteed to be between 83% and 85% ethanol. 2% isn’t going to matter and is well within the correction range for closed loop operation.

Just putting that out there. While an ethanol content sensor and logic to support it would of course be the best, sourcing quality fuel and just using a static map will work too.