Jets in hat?

Discussion in 'PSI Superchargers Tech Questions' started by willys33, Jan 12, 2009.

  1. willys33

    willys33 new

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    Putting a new hat onto my high helix, retro roots blower and I noticed the jet size decreased front to back (car application, not boat). Read the different post here you talk about the blower moving the air forward. Would it make since to put the larger jets in the back, so the fuel is pushed forward, cooling the blower and mixing better?


    TX's

    Mack
     
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  2. Mike Canter

    Mike Canter Top Dragster
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    Mack, I remember that discussion. On a HH the air going into the top of the blower goes to the back of the rotors at a step angle. The air coming out of the bottom comes out of the pie shaped hole at a step angle forward. So if you have the hat off and you stand in front of the blower and put a long wooden dowel or yardstick so one end is all the way back on the outside of the rotors and you hold that yardstick at about a 45* then that is the angle the air is going in.

    I believe the logic for having the jets decrease in size as you go back on the top is because it has less job of lubrication and cooling in the top back because all the forward jets are also adding fuel that is moving towards the back.
     
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  3. willys33

    willys33 new

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    Hat Jets

    Thanks Mike.

    Do you use large jets on the lines going into the rear of the blower and a larger jet in the right side verses the left side?
     
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  4. Mike Canter

    Mike Canter Top Dragster
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    The jets normaly start large in the front of the hat and progress downwards in size all the way to the back of the blower. The jets from one side to the other are always paired with the same size. Since the air mixes pretty well before and as it is exiting the pie hole it doesn't really help in having different jets on one side than the other.

    The size of individual jets in the hat and top of the blower are not as critical as the total area of those jets in the tuneup. A lot of guys use what ever jets the have available as long as the total area is correct.

    Make sure that all the nozzles in the hat and the top of the blower have the single small air hole in the side. That is important and a must have.

    The amount of fuel going through the hat normally a percentage of the total fuel flow into the motor. You want as much fuel going into the hat 65-75% as you can get so you get lubrication and cooling of the blower. So as you go up in OD and you need more fuel you can make the hat and top blower nozzles bigger and keep the ports close to the same.

    Some examples of jet sizes normally used (these would be pairs) starting from front to the back are: for around 20% OD maybe 48, 46, 45, 44, 42. For middle 30% OD maybe around 57, 55, 54, 52, 50. More OD may require bigger jets.
     
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  5. LeWhite

    LeWhite BB/Alt

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    What are you suppose to do if you have two or three holes that constantly idle cold? I'v got a pie HH set back almost five inches with port check at 10 psi
     
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  6. Creech

    Creech Member

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    Like Mike said; the blower needs more fuel the faster you drive it. Not to the same extent on a screw but still.
    Fuel will heat up a cylinder at an idle, like puttin the choke on. i.e. the dribbler.
     
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  7. SoDak

    SoDak Active Member

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    On my stuff I have the back blower nozzles being the largest and only 2 nozzles in the hat. 2 in hat and 6 in blower. My thought process being that the fuel coming into the blower via the injection hat probably won't get to the top back of the blower.
    I've run for several years like this without seeing any signs of it being completely wrong nor to my advantage.

    Mike, your one comment sparked a question. On a roots blower deal, how would the engine performance change if you suddenly changed the aerated hat nozzle bodies to non-aerated?
     
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  8. Mike Canter

    Mike Canter Top Dragster
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    Good question. The aerated nozzles serve two purposes, they suck in air and mix with the fuel to help atomize the mixture when fuel pressures are low at idle and staging and also break siphon when you let up at the end. This is a pure guess here is that the mixture at idle and stage would go a little leaner because of better atomization but the overall wide open tuneup probably would not change much.
     
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  9. SoDak

    SoDak Active Member

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    Once I had large enough nozzle jets in the back of the blower where some of it came out the aeration hole.:eek:

    I'm thinking on a blower deal, especially frt discharge, the blower must be screwing up some of the suspended fuel, forcing at least some fuel to drop out of the air.
     
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  10. Creech

    Creech Member

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    Most pro mods have 2 or3 cylinders with dribblers in them. The hat nozzles distribute fuel at idle but the barrel valve meters it.(just a reminder)

    I cant seem to post pictures here or I'd put up a picture of a pro mod with an extra nozzle in 1,2 and 4 cylinders. This is usually done with 3to5 pound check nozzel bodies. with lines coming off the hat distribution.
    Say you have a .057 nozzle jet in #2 cylinder and its going dead @ idle the port check is probably @ 12psi when the cylinders dead and you open the flow to the .057 it cant take it and stays dead.
    a .057 is .002551 square area a .040 is .001257 in a low presure check open at an idle wakes up the cylinder then a .040 in the port nozzle= the .057 that was in it. The reson for the 3 pound check nozzle body is to keep vacuum in the manifold @ idle from sucking fuel from the hat.
    Maybe someone can explain this better than me but this is what the promods do.
     
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  11. LeWhite

    LeWhite BB/Alt

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    Are you saying that cyl #2 idles with its share of hat fuel at idle plus a 040 idle dribbler and a 040 run nozzle? Will that make #2 idle hotter?
     
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  12. Creech

    Creech Member

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    That's what I'm saying. #2 and/or whatever cylinders are to cold. It would be better to have Darren Mayer or someone who's done this more than I explain. I think of it as putting the choke on. Ive seen pro mod's with dribblers in #2 and#4 and others with them in #1 and#3 some with them in #1 #2 and #4 depends on on lot of variables I guess. blower,cam? how much fuel and wear in the hat? The reason for them is most definitely for the cold cylinders.
     
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  13. LeWhite

    LeWhite BB/Alt

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    Put more fuel in a cold cyl? counterintuitive!
     
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  14. Creech

    Creech Member

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    Have you ever tried it? Ive used dribbler systems. Call enderle or DMPE.

    Have you ever started a 20 degrees cold motor without a choke. Wont run. Choke it, starts and warms up faster. Why?
     
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  15. Mike Canter

    Mike Canter Top Dragster
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    I think you are getting off on a tangent with the choke system on a carb car comparison. The problem with a cold motor at 20* is that the fuel will not atomize so it stays liquid and will not get into the cylinders in a vapor form. With no vapors to ignite it is real lean and too lean to ignite and if one cylinder does ignite all the pooled liquid fuel up the intake runners also ignites and backfires back through the carb. By putting on the choke your are choking off the air flow hence the name choke. Choking down the air flow changes the cold AFR so the mixture will fire in the cold. I beleive that is opposite to what you are saying with the dribblers. I was under the impression that the dribblers are used at idle to put more fuel in the lean cylinders to cool them down. Dunno maybe I have always thought it backwards.
     
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  16. Creech

    Creech Member

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    Mike
    the chokes on my 44mm yamii mikunis dont have air valves they add a fuel circuit. if i choke 1 carb a little even with the with the motor warm that egt raises.
    the meter rods have to be in the right notch and the mixtures just right for the weather or this little 1976 440cc wont run. i still go backwards sometimes. sometimes twice! goes 90 in the 1/8 may not sound like much but its a lot more fun than ice fishin'!!

    Le
    which cylinders are dropping?
     
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  17. eli

    eli Banned

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    Mike the dribblers normally come in at 5,000 RPM more or less the way the poppet is set.
     
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  18. Creech

    Creech Member

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    Eli
    I think you mean the ports..driblers are idle(sometimes called primaries).
     
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    Last edited: Jan 19, 2009
  19. LeWhite

    LeWhite BB/Alt

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    Why have a dribbler that runs the same way the poppet runs? when you can just have a bigger port nozzle
     
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  20. Creech

    Creech Member

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    if you put in a dribbler without atleast a #3 check it will change the hat distribution and throw you a curve..different part of the intake go cold???
     
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