Results 1 to 6 of 6

Thread: First pass at e85 with the Atomic TBI

  1. #1
    Join Date
    Sep 2018
    Posts
    3

    Default First pass at e85 with the Atomic TBI

    Basic Engine Info:
    1995 Ford 302
    9.8:1
    Comp XE 266HR
    AFR 165 Heads
    Edelbrock Performer RPM Dual Plane w/ 1" Spacer
    MSD Pro Billet Small Cap distributor, 6AL2, MSD 8253 Coil
    Timing Control Active - still dialing in curve once I have more drive time on this set-up
    11 deg initial advance (cam has zero overlap at .050" so I may dial back some initial advance)
    Zero Vacuum Adv
    36 Total @ 2500rpm

    Strong stable idle @ 825rpm in gear
    Pulls 15-18" vacuum at idle
    IAC 0 at free idle, 16 in gear holding the brake. Seems like it is still learning my new set-up so this may get dialed in a bit more.

    Have not driven the car much since I converted to e85 so I will post back my final settings (waiting on a new Lokar throttle cable to arrive).

    I'm currently using the Mild Cam settings as a baseline. I anticipate this will change but for now the motor likes it at idle. I have a second wide band and it tracks closely with what the TBI ECU shows on the handheld (since the addition of the 1" spacer). I am using the pump gas calibration on the 02 sensors since I can use Lambda to convert/compare back to an e85 scale.

    Fuel delivery is Aeromotive A1000 in tank pump, -6an feed/return lines, and an Aeromotive return style regulator. I have fuel pressure set at 58psi for now. Will experiment with bumping that up once everything else is dialed in and happy.

    My initial target AFR settings (Note this is using what I believe to be a pump gas scale in the 02 sensors and these are not road or track tested):

    Idle = 12.8
    Cruise/part throttle = 12.3
    WOT = 11.8

    Overall I like the look and and function of the Atomic TBI. Everything seems to be very good quality. At some point I want to add a Race Pak dash to be able to data log. I tune my Duramax using EFILive but can also appreciate the simplicity this offers. My goal is to see how far (and fast) I can take this little motor with this set-up. Both on the street and racing in the local stock block NA class.

  2. #2

    Default

    Quote Originally Posted by JPowell29 View Post
    I'm currently using the Mild Cam settings as a baseline. I anticipate this will change but for now the motor likes it at idle. I have a second wide band and it tracks closely with what the TBI ECU shows on the handheld (since the addition of the 1" spacer). I am using the pump gas calibration on the 02 sensors since I can use Lambda to convert/compare back to an e85 scale.
    ...
    My initial target AFR settings (Note this is using what I believe to be a pump gas scale in the 02 sensors and these are not road or track tested):

    Idle = 12.8
    Cruise/part throttle = 12.3
    WOT = 11.8
    Are you saying that you have scaled the numbers for posting on the forum, or that's what you put into the unit?

    You shouldn't be scaling numbers - put the numbers into the unit as if you were running pure gasoline (i.e. stoich = 1lambda= ~14.7 displayed in the unit).

    The ECM has no awareness of what kind of fuel you're putting into it, and the O2 sensor is merely detecting whether or not you're at lambda. The scaled numbers in the unit are a convenience value. It's kind of unfortunate as it tricks many people into thinking there's more to the system than there really is. That's including myself, when I first started learning about ECM tuning - I made the mistake of commanding AFRs for E10 rather than pure gas. Particularly bad in a narrow band system as the car will never be able to hit stoich in closed loop.

    To be succinct and assuming these numbers are what you entered into the handheld: all of your numbers are very rich. I'd generally shoot for stoich(14.7) at idle and cruise, although with systems like these a slightly richer idle may be in order since it's a bit harder to meter fuel coming in from the throttle bodies at slow engine speeds.

    I believe I'm running ~14.5 idle, 14.7 or maybe 15.0 cruise (a little leaner for fuel economy, with pump shot and PV taking care of throttle transitions) and ~12.5 WOT. I have not dynoed the car so I went a little conservative on the WOT AFRs. I'm running somewhere around E10 fuel in California.

  3. #3
    Join Date
    Sep 2018
    Posts
    3

    Default

    Are the fuel maps in the ECU created based on a pump gas calibration? How would running AFR in the 14-15 range deliver enough e85?

  4. #4

    Default

    This is pretty tough for me to explain as, frankly, the concept of the "afr" unit is more than a bit convoluted in ECMs.

    There's some good reading here (https://www.hotrod.com/articles/wideband-oxygen-sensor/), particularly on "meter correction".

    MSD's ECM is going to be scaling numbers from lambda units to afr units. The issue is that lambda values from a lambda (oxygen) sensor are the same regardless of the fuel being used. They measure how much oxygen is in the exhaust. 1lambda = stoichiometric.

    If you were running pure gas, 1L=14.7afr. With E85, 1L=9.765afr. The trick, though, is if you were running a stoichiometric air-fuel ratio(regardless of pure gas, E10 or E85) your Atomic EFI (and most wideband displays) would read "14.7". Essentially, it is taking 1L and multiplying by 14.7 to display a value.

    The "commanded AFR" is the same thing, but in reverse. You command 12.8, it divides by 14.7 to get the lambda value it should expect to see at the oxygen sensor.

    So if you're with me this far, great! The easy thing is that stoich is 14.7 so for idle and cruise you can use that as a baseline. Max power for E85 is what you'll want for WOT, and there's a range there: 0.7143(richest) - 0.8673(leanest). You want to scale those numbers by 14.7(stoich for pure gas), not 9.765 (the stoich for E85).

    So to answer your question, yes, the base fuel maps for that ECU most likely assume pump gas. If I were tuning your car, I would want to start with a fair bit richer idle/cruise/WOT so that it's skewing richer to make up for that. Once it learns from the fact that the fuel isn't behaving the way it expects, then you can skew back to the values you want.

    I'm kind of wanting to make a YouTube video on this subject, because it's actually a very common confusion.

  5. #5
    Join Date
    Sep 2018
    Posts
    3

    Default

    The article was a great read as was your explanation. I love learning something new, thank you for the insights. Before jumping into the e85 switch I spent time reading through data from Mark Sullens (e85 carb builder and tuner). Having TBI, I felt using some known e85 benchmarks (from Mark and his customers) for carbs would be a good place to start. I agree the 12.8/12.3/11.8 are going to be rich. I would rather error on the rich end until I better understand how my car behaves on the Mild Cam profile/fuel tables. I should have the car back on the road this weekend and will post up my learning curve.

    John

  6. #6

    Default

    Thanks John. I think that's a good idea for first fire and a few test drives. Once the AFRs stabilize for idle and cruise I'd recommend going up around 14.7.

    You may want to look at the WOT numbers though - "11.8" ends up on the high side of mid-range for E85.

    It sounds like 10.5-12.8 would be the range you'd want to set to hit the right commanded lambdas for WOT. (numbers like 10.5 give me the heebie-jeebies though, that's approaching bore wash territory with pure gas!)

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •