vacuum in the hat

Discussion in 'Manton Push Rods Top Alcohol Tech Questions' started by craig moss, Dec 28, 2008.

  1. craig moss

    craig moss Member

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    What are the odds that a bird on a 14-71 hh delta at 52 over and 78-7900 rpm would have a vacuum present in the hat? Just wondering and how much boost coul:confused:d it rob? thanks Craig
     
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  2. Creech

    Creech Member

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    High.... I don't know how much boost exactly but as far as horsepower ; hundreds.
     
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  3. SoDak

    SoDak Active Member

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    I've always wanted to data collect with a vac sensor in the hat also.

    Veney told me with a HH 14, switching from a plain jane birdcatcher to his injector expect about a 4 psi increase.
     
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  4. TWD

    TWD Blown alky

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    I've heard similar results (4 psi) when people switched to Veney injectors from a standard bird injector. It's probably the same for Gerardot and Big and Ugly injectors as long as the butterfly size is identical.
    Regarding vacuum I think you may be at 1 psi under atmospheric pressure, but I've never bothered testing it.
     
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  5. Fuel Cars

    Fuel Cars AA/AM

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    I could be all wet, nothing new, but, as long as the hat is connected to a blower that is turning in the correct direction, the hat, at some point, will see vacuum because of the pressure differential.

    Although you didn't specify where the vacuum is present, I would suspect at the throttle blades and the opening between the blower lobes, anywhere else and I would think it could be considered leakage.
     
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  6. SoDak

    SoDak Active Member

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    I think Craig Moss is assuming that if the hat is in a vacuum (under full throttle), then that means it is a restriction to the blower. I would assume the same thing.
     
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  7. Fuel Cars

    Fuel Cars AA/AM

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    The air entering the hat is slower than at the lobes under any speed so there will always be some vacuum, if there isn't, the blower's not turning.

    If Craig meant areas of dead-flow, that would be the hat internal shape and would require a different scoop like the Big Ugly.

    Btw, correctly shaped restrictions increase the pressure such as a carb.
     
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  8. SoDak

    SoDak Active Member

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    I understand what you're saying but my understanding is we're talking a psi reading in general in the hat, not localized areas.

    I would love to map an injection hat just like mapping a cylinder head port.
     
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  9. Mike Canter

    Mike Canter Top Dragster

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    It may take a little time but I am going to get hold of a friend of mine who is a aerodynamists and has designed injector hats. He knows all that kind of stuff. The problem is they are all shut down for the holidays right now. Stay tuned.
     
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  10. craig moss

    craig moss Member

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    vacuum in th hat

    I Did Get A Big &ugly Was Wondering If I Would Make Any Gains Due To Change In Air Flow To The Rotors The Butterflies Are 5-9/16 On The Bau Thanks Craig
     
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  11. 560Jim

    560Jim Member

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    Vacuum/pressure ? in hat

    We have just recently hooked up a RPM data logger and included a MAP sensor in the hat. This is a 8/71 standard helix/ teflon/nylatron with a BAU with the middle sized butterflies(cant remember the size). Just checked the traces and found 17-20 inchs vacuum at idle (surges slightly) and at the hit it went to zero (no suprises there). The zero quickly turns to a small pressure and at the big end (190`s) it had risen to 1.5 inchs pressure. I never had a chance to test the old enderle but it wouldnt surprise me if it never made it into the pressue zone. By the way, the blower turns max 11700 RPM and makes 23lbs when fresh.
    Cheers. Jim
     
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  12. Mike Canter

    Mike Canter Top Dragster

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    That is the way I think it will work. With butterflies closes at idle or barely cracked you will draw a vacuum. When going to the track then the air is being forced into the hat and positive pressure will start and the faster you go the more the positive pressure from the airflow into the hat.
     
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  13. Fuel Cars

    Fuel Cars AA/AM

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    Mike, do you think the air entering the hat is slower than the blower?

    Isn't the purpose of the blower is to increase boost by increasing the volume and air speed?

    At some point where the accelerated air is derived from the incoming air, there will be some vacuum. That point may move from the front of the hat to somewhere in the acceleration transition point?
     
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  14. Mike Canter

    Mike Canter Top Dragster

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    The purpose of the blower is to increase air volume to the motor. I think that air velocity is a by product of what is happening in the blower. The reason the injector hats are bell mouthed and facing forward up in the airstream is to take advantage of the ram air effect created by the forward movement of the car. The faster you go then the more air is rammed into the hat and this gives you a slight increase in boost. I do know from discussions with the aerodynamist friend that any bend or turn in the incoming airflow decreases the flow. If you have a 90* abrupt bend then you lose 50% of the airflow and the same goes in hoses. Also in a Rootes HH blower the air comes in at a steep angle from the front and enters the top of the blower at the back of the upper opening. So if you look into the opening of a well designed hat you should see the rotors in the back of the opening in the top of the blower. Take a look at the two hole hat that JFR racing uses and see how low it sits and how far forward the opening is. This is the angle at which the air enters the blower. The design is to reduce any changes in the direction of the airflow and aim it at the correct point of entry into the blower opening. The front part of that blower opening is not really used. This was taken advantage of in the Kobelco Superman by moving the rotors to the back of the longer blower case. This is also why those spacers put between the blower and the hat help because the move the hat opening forward. They straighten and smooth out the air flow from the hat opening to the back of the blower inlet. Same thing happens on the bottom of the blower. The outgoing air does not go straight down it goes forward at a very steep angle and this is why the pie opening helps and setting the blower back helps. I do believe that at wide open throttle IF the hat was too small for the size of the blower or the overdrive of the blower used is too much then you might see some vacuum way down inside the hat. I don't believe that there are any hats made that small. Why would somebody make a hat that small? I really think that most hats are designed well enough that positive pressure will be seen while the car is moving down the track.
     
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  15. SoDak

    SoDak Active Member

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    I agree with Mike fully.
    We've had interesting conversations about this stuff before, a search should reveal more info.
     
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  16. lucky2wd

    lucky2wd Member

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    What if you don't have air force into the front? Such as pulling, We have maybe 30 mph ground speed and that is maybe half the time. Would the old Enderle barndoor be any good? maybe moved a little forward too?
     
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  17. Mike Canter

    Mike Canter Top Dragster

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    Then you only have the boost the blower is making. No free air from fast ground speed. At 30 MPH is doesn't make much difference which direction it is pointing. The shape of the injector hat still comes into play on how straight and smooth that airflow is from the front of the hat to the back of the rotors.

    Just to add something here. Remember when that ProMod had that high thin four hole hat turned 90* so it was straight up like a shark's fin. Stop and think here when the air came past the butterflies and made an abrupt 90* turn down (lost airflow) then went down to the blower where it made another almost 90* to the back of the blower. (lost airflow again). Add those two losses together....wow. My friend, the aerodynamisist, is the engineer that designed the two hole hat for John Force Racing. We spent some time discussing that shark fin hat.
     
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  18. SoDak

    SoDak Active Member

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  19. Fuel Cars

    Fuel Cars AA/AM

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    Mike, has your aerodynamisist friend done any testing relating to the effect the boundary-layer has on the flow around the hat?
     
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  20. Mike Canter

    Mike Canter Top Dragster

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    Yes he has.
     
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