Blown Alcohol Air Fuel Ratios

Discussion in 'PSI Superchargers Tech Questions' started by Mike Canter, Mar 11, 2004.

  1. Mike Canter

    Mike Canter Top Dragster
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    I was wondering if anyone has done any real time measurements of Air Fuel Ratios for a blown alky motor. Does anyone know what the best AFR for power is? Gasoline is 12.8:1 so what is alcohol?

    Has anyone used a wide band O2 sensor (UEGO) on there blower motor?
     
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  2. Hemi Parts

    Hemi Parts Top Fuel

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    Generally accepted is that gasoline is a 14:1 fuel and alcohol is a 6:1 fuel.

    Bill
     
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  3. Mike Canter

    Mike Canter Top Dragster
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    Bill, that figure of 14:1 for gasoline is stoichiometric (which actually is 14.7:1) and is the point where 100% of the fuel is burned as is the 6.7:1 you mentioned for alcohol. Those figures are way too lean for a race car. A race car on gasoline is normally set up for 12.4 to a 12.8:1 for max power. What I was looking for is that max power ratio for alcohol. I have heard it is 4:1, then I have heard 4.5:1. I was trying to find out if anyone out there had ever really measured it like on an engine dyno run. Appreciate the input. Looks like you are the only one that is going to answer me.
     
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  4. Hemi Parts

    Hemi Parts Top Fuel

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    My guess is Fred Mandolini or Tom Conway would be best suited to answer those questions or perhaps Brad Anderson. If I was a betting man I would bet that Fred has actually done the most research of that particular type basede solely on what I have been told. I would contact each of them since none of really knows what they have done in the wee hours of the night.

    Bill
     
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  5. Mike Canter

    Mike Canter Top Dragster
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    Great sugesstion. I have talked to Tom Conway, Ken Lowe, Kinsler and Enderle already. Somebody out there has to have run a blown alky engine on a dyno with a wideband O2 sensor. How do I get hold of Fred Mandolini, you can email me at mike.c@mindspring.com. A good idea with Brad, I will call him also.

    I understand the VE going down when the roots blower rpm goes up and that you have to pull out fuel to keep the mixture (AFR) correct. My question is are tuners really trying to keep the AFR (guess) of 4.5:1 constant throughout the engine rpm range. We all look at EGTs and the plugs to see if it is correct but we are really checking the AFR and the plugs really only reflect the engine performance in the final part of the run.
     
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  6. Dave Flanders

    Dave Flanders New Member

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    I'd love to hear if you can find some solid info on this, I've been looking for a while now and haven't had much success. This is what I have learned -

    Check out www.HRE.com - they claim 4.5:1 for best torque down low and pull fuel out to 6:1 for best power on the top.

    A friend of mine runs a turbo alcohol 2.3 Ford and he runs 4.5:1 all the way through.

    Watch what wideband you're using for comparison, they don't all read the same.
     
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  7. Mike Canter

    Mike Canter Top Dragster
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    This is not a Honda type wideband sensor it is a totally calibrated unit that costs $1200. (don't tell my wife) I just had it back to the company that made it and they checked it from 3:1 to 18:1.
     
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  8. OzAlky

    OzAlky Member

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    I was told that the best O2 sensors that money can buy have a limited range, and it seems that a Blown Alky engine probably runs outside this range (too rich). I assume that some of the fuel that goes into these engines is not able to be combusted in the short amount of time it's there, as the droplet size is too large - so it ends up being used basically as coolant for pistons, chambers , valves, etc.
    I know of 2 guys who have run O2 sensors on Blown Alky engines - one of them claims he gets worthwhile data, the other guy took the sensors off because they fell off the scale under power every time.
    These were on Aussie Doorslammers which are probably run richer than FC's or Dragsters because they are harder to get down the track.
    If there is a sensor available that will read over a wider range, I'd be interested in trying it, but I've been told it's not possible.
    Where did the sensor come from Mike ?
     
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  9. koanui

    koanui New Member

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    Mike you can also try giving norm drazy from psi a call he might be able to answer your question. just be ready for the long version. [​IMG] [​IMG]
     
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  10. Dave Flanders

    Dave Flanders New Member

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    I'm wondering if that's the problem with using a wideband on a blown alcohol as opposed to a turbo motor. I would think raw fuel coming out the pipes would affect the readings, on a turbo there is more heat in the pipes to help burn the excess.

    I run a turbo alcohol motor and have noticed that even slight misfires (which put unburned fuel in the exh.) drop the EGT considerably, what would this do to a wideband reading?
     
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  11. OzAlky

    OzAlky Member

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    Yes Dave, you just have to watch the Alky cars clear the pipes and stage - there is raw fuel just spraying out the pipes.
    A long way from stoichometric I would say.
     
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  12. Mike Canter

    Mike Canter Top Dragster
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    I have a special shield on my O2 sensor to protect it from the large alcohol droplets while idling and staging. It doesn't hurt the sensor if the sesnor is turned on and heated up first.

    OzAlky, my system goes to 3:1 AFR it comes from EMCO and costs $1200. It is very accurate and can be easily calibrated at anytime while in the car. It uses the amount of O2 in the air as a calibration standard. If you want more data email me at mike.c@mindspring,com
     
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