Fuel pressure for hat and ports

Discussion in 'InsideTopAlcohol.com Tech Questions' started by MKR-588, Apr 14, 2019.

  1. MKR-588

    MKR-588 Member

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    Hi guys, just wondering how much difference you would expect on fuel pressure at the hat and at the ports? My customer has a sensor on the hat distribution block and another at the port distribution block. He also has a sensor on the outlet of the pump. At full throttle it shows around 125lbs pump pressure, around 78 at the ports and 112 at the hat with around 26 lbs boost and 7200 RPM. He has a "T" fitting after barrel valve were the lines go to each distribution block. Are these differences acceptable and why so much difference. Please explain or do we have sensor problems.
     
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  2. Mike Canter

    Mike Canter Top Dragster
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    That is pretty normal. The reason the port reads lower than the hat is that the port flow goes through a check valve. What ever the spring pressure is when the check valve is wide open subtracts from the flow pressure and also you have eight port nozzle jets that total area is probably more than the total area of the hat jets. Plus compared to what is coming right out of the pump will drop going through the barrel valve because of the main jet returning fuel to the tank
     
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  3. Bjs344

    Bjs344 Member

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    I would hook them all three to shop air (or at least two at a time into a tee, then swap out the combinations). I bet you find a mismatch between the pump sensor and the hat sensor unless you are currently running a blank in the main.
     
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  4. Mike Canter

    Mike Canter Top Dragster
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    But what he is seeing is normal
     
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  5. MKR-588

    MKR-588 Member

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    Thanks guys. I might just change over the pressure sensors on the distribution blocks just to see if they stay the same for curiosity. Currently run a .046 nozzle in #1 and a .033 in #8 with everything in between. Do you think we could even then up a bit closer if we were to increase the system pressure? If so , how much would you aim for . Application is circuit boat with 1471 std helix @ 28% and 2" setback.
     
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  6. Mike Canter

    Mike Canter Top Dragster
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    WIZBANG and bandit496 like this.
  7. MKR-588

    MKR-588 Member

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    Thanks Mike, looks like our pressure is close enough. Will start to close up our port nozzles as they are way safe at the moment according to plugs, yet EGT are around 1100-1220. Comparing the plugs and EGT readings, they dont seem to line up very well so I tend to go with plug readings more so.
     
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  8. Mike Canter

    Mike Canter Top Dragster
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    You should find out why your EGTs are that high before you lean it out. Could be the position of the EGTs are too close to the head or your Ignition timing is too retarded and moving the flame/heat out of the combustion chamber into the exhaust.

    What plugs are you using?
     
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  9. bill

    bill Member

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    when egts go bad do they not show a reading or do not show accuret reading I got some that are 200 diffrence
     
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  10. Mike Canter

    Mike Canter Top Dragster
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    They either flat line or real low and look like noise. Never seen one fail and read a high temp. It would be unusual for all of them to fail and all read a high temp.
     
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  11. MKR-588

    MKR-588 Member

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    Mike, plugs are NGK R5671A-10. After a couple of 450 meter straights it only burnt around 20% of the cad on the flat of the plug above the threads. Timing around 32° but cant say how accurate that would be as owner is running an offset which is belt driven { yuk ] and timing does retard as revs go up. I do set timing holding the revs up but cant say exactly what is is at 7500 RPM. Have told him we need to go to a crank trigger with the next motor we set up. It is very difficult to bump up the timing another degree or two because of this setup. Timing changes as the motor rolls at idle. I might see how far the probes are inside the pipes. Its a Motec data system. Do you know how deep they should be and distance from the cylinder face?
     
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  12. Mike Canter

    Mike Canter Top Dragster
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    I have always installed the probes 2 to 2.5” from the head. And closer than 1.5” will reduce the life of the probe. The tip of the probe should be as close to the center of the tube. Probes mounted on the top will read hotter than probes mounted through the bottom of the pipe. The normal safe max temp of an EGT on a alcohol motor is 1050* F but if running just an 1/8 mile then 1100* can be safe.
     
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  13. MKR-588

    MKR-588 Member

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    Well as mentioned Mike, plugs don't show excessive heat at all and our straights are usually around 550 - 650 metres. Our testing the other day was only on a 450 meter straight hence why I didn't chase the tune and left it until we tested on the longer track. I will get customer to check probe location / depth and see how it pans out. Timing may be a bit of an issue to get set reliable due to the belt driven offset. It really is a pain in the ass. Crank trigger is the go without doubt.
     
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