Pressure / flow /RPM

Discussion in 'PSI Superchargers Tech Questions' started by Bjs344, Mar 1, 2021.

  1. Bjs344

    Bjs344 Member

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    Scratching my head here. New 990 pump, some run time but doesnt actually have a full pass on it.

    Didn’t have any data on the first few attempts. Since I started measuring pressure, it won’t open the port check.

    system pressure at 8k should now be 230 but can’t get there to find out.

    goes 5400 in the brake. Making about 30 psi fuel pressure and 32 psi boost. So no port flow. Put a wideband on and it goes 5.7 on alky scale. Super lean.

    anybody can convert expected flow and pressure at 8000 rpm vs 5400? I’ll scout my old textbooks tonight but hoping somebody has it handy. Worst case I’ll take the pump off and get it closed again but still ave the 15.8 flow tag and maybe an hour or two or run time since.
     
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  2. kosky racing

    kosky racing Comp Eliminator

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    Signs of a bad pump- they fail at any time
     
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  3. Mike Kern

    Mike Kern Member

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    Make sure you don't have something dumb like the cover was removed and not clocked properly during install. I've seen it...it will run but not very well.
     
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  4. rhansenml

    rhansenml New Member

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    make sure shut off valve is shutting off return, it will run with the return open just no pressure
     
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  5. Bjs344

    Bjs344 Member

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    Thanks for the feedback. I checked the shutoff with shop air. Air goes where it’s supposed to. The notch on the pump is on the right if the pump was vertical and you’re looking at it from the front. It’s belt driven but flipped around like a cam drive. I had it backwards when I first put it on and it did nothing.

    I was going to put my old 990 on but I’m not sure I can clock it right (old style housing vs new billet rotateable one that’s on the car).

    I might try to run the pump up to alky digger on Friday.
     
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  6. Mike Canter

    Mike Canter Top Dragster
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    Why system pressure at 230 lbs at 8k? That is really high. I like to have 125-130 lbs at 8000. Are you measuring pressure at the pump? The normal port poppet crack pressure is around 18 lbs. there is a big difference to pressure measure at the pump to pressure measured after the BV.
     
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  7. Bjs344

    Bjs344 Member

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    Mike, I set it up around 140 at first. Fought ignition issues. Got them fixed and put a pressure transducer in the port distro block. Knocked the blower off at 200’ and only ever read boost pressure in the port distro.
    So I moved nozzles around to get a calculated 175, added a temporary mech gauge at the pump outlet and put a wideband on. 6.45 afr and still just boost in the port distro. Mech gauge showed about 40 or 50 on the pump outlet (really bouncy, almost like pump is cavitating).

    Moved nozzles again to get calculated 215. Stall check, 5.7 afr and it cracked the port check right as I let off the throttle. Port pressure rose to 49 psi momentarily. Didn’t get a good reading off the mechanical gauge.

    Was going to reduce nozzles again to get a calculated 235 max pressure but I’m leaning toward the pump is broke so will take it apart and inspect and then probably run to Nashville.
     
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  8. Mike Canter

    Mike Canter Top Dragster
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    My recommendation is to get the system flowed and be given a tuneup. The $800 spent on that is probably cheaper than paying to repair things and you will start having fun faster. In tuning Alky motors we normally compute the tuneup at 8000 or 9000 depending on where the shift is. Also look for a fuel pressure at the pump of around 125 lbs at 8000 rpm. The way I read what what you are doing is resulting in you chasing your tail. Set your idle return poppet at 9.5 lbs crack and your port at 18 lbs crack pressure and keep those constant. Trying to read AFR with a wide band is really hard because it reads all over the place in first gear. If you have 32 lbs of boost at 8000 rpm you need right at 12 gpm at 8000 rpm. Then tune by reading your plugs or by EGTs.
     
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  9. Bjs344

    Bjs344 Member

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    Mike, I’ve set up multiple systems. Never had a problem. This one threw me for a loop.

    Afr was dead steady on the converter.

    At this point I’m pretty sure it knocked the blower off because something happened to the pump. Just trying to make sure it’s not the tuneup but don’t see how it could be at this point.

    It will make 37 psi of boost at 8000 and if I put 12 gpm through it would not only shut off, it would probably hydraulic and kick the rods. Careful with those rules of thumb.
     
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  10. Mike Canter

    Mike Canter Top Dragster
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    How are you computing how many GPM you have? My figures are all backed up by flow meter data. What size motor is this?
     
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  11. Bjs344

    Bjs344 Member

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    Teeny tiny
     
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  12. lucky devil

    lucky devil Member

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    12 GMP is safe at 32PSI , this is a number I have used from data also ....going down to 9.30 would be really on it. again , this is from my own experience but I do agree with Mike in getting the whole thing flowed first.
     
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  13. Bjs344

    Bjs344 Member

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    Doesn’t work that way. You don’t even know the motor size, you can’t possibly guess at gpms.

    When somebody flows a complete system, how do they account for boost and its effect on total area. The main thing I’m interested in is what rpm do the ports start flowing and I don’t see how somebody can tell me that with certainty on a flow bench.
     
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  14. Mike Canter

    Mike Canter Top Dragster
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    The big thing on port flow is having them off at idle and on right at launch. You want the port check valve set at the lowest pressure that is above idle pressure. 18 lbs crack pressure is pretty well the safe standard for this unless you have a weird tuneup. It doesn’t make much difference if it is set at 16 lbs or 24 lbs because the pump pressure jumps up really fast when the engine rpm goes up. If you set the check valve too high you can get a slight hesitation on launch. You can check the opening by taking a port fuel line loose from the nozzle put it into a plastic jug and having somebody run the engine slowly from idle on up and see what rpm it starts to flow at. The higher you set the pressure of the check valve the lower the pressure is going into the nozzles. The set pressure of the check valve subtracts from the total fuel pressure going into the port nozzles.
     
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    Last edited: Mar 3, 2021
  15. Bjs344

    Bjs344 Member

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    I don’t know if this thing is weird because it’s so small or what. I’d never paid much attention to port opening point before I realized that’s why I knocked the blower off. Pump pressure has to exceed boost + port check before ports will flow. I wouldn’t think it would be exact due to a slight area difference on opposite sides of the port check poppet, but it looks pretty close. Port check cracks at 15 psi when I test it and about 45 psi on the car with ~31 psi of boost.

    Originally I had about 30 psi fuel pressure on the converter with 30 psi boost. So nowhere close to opening the port check at launch.

    I put my old spare pump on last night and just did one quick throttle whack. Looked about the same on the mechanical gauge. The car shuts off the damn laptop when I wack the throttle and I didn’t hit the button to record onboard.

    I’m going to reduce the port crack slightly (although I don’t have much room before they’re open at idle) and take just a little more blower nozzle away and then I think the ports will be solidly open on the converter.


    I also though about raising the pump sizer check to about 50 psi but then the ports will be flowing on the 2 step so will probably have to add a converter helper. At least That’s easier to deal with than another boomer
     
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  16. Mike Canter

    Mike Canter Top Dragster
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    Are you using Alky Pro or Jetsize software. Also you never did tell us what engine and it’s cubic inches
     
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  17. Bjs344

    Bjs344 Member

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    FIE

    326 Chevy
     
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  18. Mike Canter

    Mike Canter Top Dragster
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    So with 32 lbs of boost are you figuring around 7.5 gpm. If it is around that then you have way too much pump and may need to underdrive it.
     
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  19. Bjs344

    Bjs344 Member

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    Interesting that you say that about the pump. What is the benefit of a smaller or slower pump vs using a pump sizer loop? Too much turbulence in the tank? I’ve had combos with as much as .250 in a pump sizer and never noticed any problem. This one currently has a .135 and that will get smaller. This is all just a shake down tuneup; boost will go up (and nozzles changed, port activation rechecked, etc) as soon as I can satisfy myself I’m not going to bang the blower again.
     
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  20. Mike Canter

    Mike Canter Top Dragster
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    Well you have a pump that is designed to put out almost twice as much as you need. To try and dump the excess back to the tank will probably result in a pressure that is too high and hard to control. Also the fuel curve through the rpm range is not going to be close to correct. The pressure and flow when at idle when the pump sizer is closed is going to be one thing and then when it opens will be something totally different. There is no way flipping the throttle in the motor when the car is not WOT going down the track is going to give you any valid readings.
     
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