fuel flow maths

Discussion in 'PSI Superchargers Tech Questions' started by crashly, Sep 2, 2006.

  1. crashly

    crashly Member

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    hi,
    just trying to work out fuel flow in LB's per hr for a given horse power figure. The engine is sbc ,twin turbo , mechanical injection, methanol fuel.
    have been using the figures of 1 LB / hour = 1 hp.....
    also flowed the fuel system and the other method of .25gal / 100 hp / minute was used in calulations.
    we know what the cfm of air the turbos flow, which method is the best to work out fuel flow?
    thanks for looking.
     
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  2. Mike Canter

    Mike Canter Top Dragster
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    Here are some figures for methonal tha will help you...

    The BSFC of methanol is an average of 2.0. Which means you need to flow 2 lbs per hour for each one horsepower made.

    One gallon of methanol weighs 6.3 lbs so a BSFC of 2 equates to .0053 GPM.

    Divide .0053 into the amount of HP you are making and you will get the approximate GPM required.
     
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  3. Randy G.

    Randy G. Top Alcohol

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    "Divide .0053 into the amount of HP you are making and you will get the approximate GPM required."

    I think you mean multiply the amount of HP by .0053 for GPM.

    RG
     
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  4. Mike Canter

    Mike Canter Top Dragster
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    Duh....Thanks Randy I screwed that up.
     
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  5. Travis Q

    Travis Q New Member

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    Brake specific for turbo methanol is 2?!?! Holy smokes! That may be right for a blower motor, but a little fuel heavy for a turbo motor. I have never seen turbo methanol past 1.35, and I usually shoot for between 1.2 and 1.25. We only used 3600 lb/hr to make 2880 hp, the fuel pump is a Waterman 12.5 gallon. Am I missing something??
     
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  6. Bob Kraemer

    Bob Kraemer New Member

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    Mike,
    Been messing around with the numbers you provided and I can't figure out how you came up with .0053 GPM
     
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  7. Mike Canter

    Mike Canter Top Dragster
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    I hope this works out the second time (lol). Like I said BSFC is always computed in pounds per hour flow. So BSFC of 2 is 2 lbs per hour fuel required to make one horsepower. At 6.3 lbs per gallon that is the same as saying .3174 gallons per hour required to make one horsepower. Divide that by 60 to get GPM and that equates to one horsepower requiring .00529 Gallons per Minute. So if you make 2500 hp that means you need 13.2 GPM.

    Travis, is doesn't make any difference if it is a turbo or a rootes it still is a BSFC of 2 with alcohol. A lot depends on the volumetric efficiency of the motor but is will not vary that much. I can tell you this and that is there is no PSI or Rootes blower making 2880 HP and only using 9.52 GPM. Either you have someting wrong in your computation or you are making a lot less horsepower than what you think you are making. At 2880 HP you would be running at around 250 MPH in the 1/4 mile.

    Same goes for gasoline or gasoline with nitrous the BSFC is around .5. A good ProStock motor may get down to around .35 to .4.
     
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  8. Travis Q

    Travis Q New Member

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    I didn't do any math. Those numbers are from the dyno.

    I fully agree, there isn't a roots or screw blower motor making 2800+ with 9 gallons. But a turbo motor doesn't have to spin that blower, so it uses far, far less fuel to make the same HP. That's why the BSFC is so much less (lb/hr fuel used divided by power at the crank). We've dynoed 5 or 6 methanol turbo engines and tuned probably another 2 or 3 more on the track, and they always come in around 1.25 BSFC or so (the ones we measured fuel on the dyno, anyway), at an A/F ratio of around 4.2. NA methanol motors are around .95-1.1, depending, with a slightly leaner A/F than the turbo motors.
     
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  9. TOL

    TOL Active Member

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    Actually, there would be a big difference. BSFC is by definition, pounds of fuel per useful horsepower hour.

    If you had two hypothetical similar engines, one rootes and one turbo, both producing the same dyno power, the rootes will always have a higher BSFC due to the significant power lost in driving the rootes. Furthermore, most of Travis's stuff is EFI, largely delivered at the ports, which helps to further lower the BSFC number versus that of a wet MFI rootes.

    At equal power, and same air/fuel ratio in the combustion chamber, the rootes engine must process more pounds per minute of air and pounds (or gallons) per minute of fuel. Therefore the calculated BSFC number of the rootes engine will be larger (poorer).

    There are a few other factors which also lend to the low BSFC numbers of turbo motors, but the two mentioned above are the big ones, irrespective of intercooling.
     
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    Last edited: Sep 2, 2006
  10. crashly

    crashly Member

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    fuel maths

    ok, to cover some different opinions, i have dynoed this turbo engine , and now am trying to work out the maths to double check the figures that i came up with. Flowing the sytem , measuring the fuel, double checking against the KNOWN usages of fuel required per hp.
    ok...
    sbc, twin turbo, meth, mech injection....
    travis... you will know these engines....:p
    @ 4000 rpm eng makes 720 hp and 960ft/lbs
    @ 1.1lb of fuel /hr works out to : 720*1.1= 792
    to convert to gal/min ..... lb/hr / 5.9/ 60
    therefore 792 /5.9/60 = 2.237 gal/min @ 4000 @ 720 hp

    @ 6150 rpm eng makes 1014 hp and 900 ft/lbs
    @ 1.1 lb of fuel /hr works out to 1014*1.1 = 1115.4
    to convert to gal/min...... using lb/hr /5.9 / 60
    1115.4 /5.9 / 60= 3.150 gal/min @ 6150 @ 1014 hp

    Rpm is a non issue at this stage till fuel pump required ments of fuel is brought into equation.

    * IS THIS MATHS CORRECT?
    THANKS FOR LOOKING

    CRASHLY
     
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    Last edited: Sep 2, 2006
  11. crashly

    crashly Member

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    fuel maths

    travis, check ur email
     
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  12. TOL

    TOL Active Member

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    I don't get what you are after crashly. If you've dyno tested this motor, then what are you now trying to figure out? Did something go wrong on the dyno?
     
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    Last edited: Sep 3, 2006
  13. Mike Canter

    Mike Canter Top Dragster
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    TOL, I have thought about it and I stand corrected. You are right I forgot about the amount of horsepower consumed driving the belt superchargers that does not get out to the flywheel. I guess that does make the a difference with the turbos....sorry about that Travis.
     
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  14. crashly

    crashly Member

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    fuel maths

    dyno was real good to get a tune and know what the max hp i could gain...
    now, have to tune engine in converter car, have enough fuel to allow engine to pull up on converter( max torque) but not too much fuel in higher eng rpm.

    *dyno proceedure: start rpm 4000( no boost)- then load engine( full boost) - then allow rpm ramp up to max rpm.( with full boost)

    * in car: start rpm idle..... pull up with load to t/c stall.... then trans brake is released.... rpm ramps up etc....

    *difference: load on engine from idle to t/c stall.... do i have enough pump speed to supply enough flow???? to supply fuel requirements....

    thansk
    Crashly
     
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  15. Travis Q

    Travis Q New Member

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    Crashly - you have mail.

    Mike - no problem, glad to finally have an idea of how much fuel those blower motors actually use!! I knew it was a bunch, but.... wow. I had talked to a screw blower guy that was putting a bit over 15 gallons through the motor, but it really didn't dawn on me. Poor crankshaft!!!

    Travis
     
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