Anybody hand-port their NPI heads?

Discussion in '96-04 - 2V Specific' started by Burninrock24, Jun 5, 2013.

  1. 96blak54

    96blak54 Legend

    Messages:
    7,653
    Likes Received:
    990
    Joined:
    Feb 21, 2011
    Location:
    Ky
    Widening the exhaust floor all the way to the valve seat offers benefits and this is with just about any head. D shaped exhaust port has proven results with a broad spectrum of heads.
     
  2. Silver95bird

    Silver95bird Active Member

    Messages:
    484
    Likes Received:
    110
    Joined:
    Sep 5, 2016
    Putting a few things together here, I've been trying to understand why modulars like the cam timing on the exhaust. Let's play out a scenario here and tell me if I'm picturing this right.

    As the exhaust valve opens, it begins to pinch down around the valve guide and that limits the flow and velocity of anything behind it, all the way to the chamber. Maybe instead of removing 70% right at the opening, lets say maybe it only removes 50%. Now that bleed down time is technically shortened because the pressures are staying in the chamber longer. Also keep in mind, this makes the piston's upward motion do work pushing the air out that usually isn't necessary. Now add in the intake valve opening, with it's port restricted. Because the port is restricted behind the valve, the port hits it's maximum velocity way back there, and anything forward of the pinch has both it's velocity and it's pressure dropped before it enters the chamber. So the opening of the intake valve, with lower pressure air, meets the exhaust air that is higher than normal pressure due to it's restriction. Are we seeing reversion during overlap? With two pinched ports, I'd sure doubt at the very least that we're getting much scavenging that way.

    So, we start with a 5.4L exhaust port, which is miles better than a 4.6L port, and work the intake side as much as possible. On a SBF/SBC type head, you can get into trouble screwing with the short side radius. The 4.6L head is different. The injector's position above the port entrance forces the flow toward the floor, and it skims across the valve instead of flowing along the ceiling and making the radiused turn. Look at the intake cutaway 96blak54 posted. That picture may be the most important picture there will ever be in this thread. Look at the dispersion pattern on the port after the injector - its washed the oil off the port walls so you can see it. After that it disperses on all sides as well, which I think is a good indication of the high velocity through the restricted section. It's literally making use of every last bit of space, and it wants more.
    How narrow does that port get at different points through it?
    And how thin is the casting at the three thin spots?
    We want to maximize the port, but let's make sure we don't break through. How are you guys porting heads on an engine stand assembled, or even tougher on the vehicle, and getting all the shavings out? I'd be very concerned about missing a piece.

    It looks like after about halfway past the oil gallery it starts to open again, but the first half of that port really needs it enlarged.
     
  3. lwarrior1016

    lwarrior1016 Moderator Staff SN95 Supporter

    Messages:
    5,850
    Likes Received:
    960
    Joined:
    Sep 22, 2014
    Location:
    South Mississippi
    I did the heads on my npi 5.4l f250 while they were still in the truck. I had the cams removed so all the valve were shut. I covered the oil pan and taped off all the ports I wasnt working on. I focused on the front of the port to about half way down where the pinch is. I had a small rag shoved in around the valve while I was grinding. When I was finished I put the shop vac over the port and got out what I could then pulled the rag out with the vac still on the port. After that, I blew it out with air. Also, you can see straight down onto the valve all the way to the seat so its pretty easy to make sure you got everything. The day I put my truck back together I took it on a 1500 mile trip.
     
  4. 96blak54

    96blak54 Legend

    Messages:
    7,653
    Likes Received:
    990
    Joined:
    Feb 21, 2011
    Location:
    Ky
    Youre catching up! Keep going!

    Now about the exhaust port. The exhaust port flow capabilities after the pinch is cut out is sufficient enough. Its the valve hole size restricting camshaft profiles favoring late exhaust opening.
     
  5. Silver95bird

    Silver95bird Active Member

    Messages:
    484
    Likes Received:
    110
    Joined:
    Sep 5, 2016
  6. d.garza18

    d.garza18 Active Member

    Messages:
    459
    Likes Received:
    52
    Joined:
    Jun 23, 2017
    Location:
    TEXAS
    Very interested in this. Eager to try and do some porting while I have the engine out before I stab it. How would I go about this with no experience?
     
  7. ttocs

    ttocs Post Whore

    Messages:
    26,087
    Likes Received:
    2,893
    Joined:
    Oct 9, 2009
    Location:
    Evansville Indiana
    youtube.
     
    d.garza18 likes this.