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flathead relief?

Discussion in 'The Hokey Ass Message Board' started by jetmek, Apr 30, 2008.

  1. jetmek
    Joined: Jan 12, 2006
    Posts: 1,847

    jetmek
    Member

    anybody here familiar with a "stepped" relief mentioned in mike davidson's book? in theory it sounds like a good idea to retain material around the exhaust valve. any one have an opinion on it or actually gone that way?
     
  2. Flat Ernie
    Joined: Jun 5, 2002
    Posts: 8,410

    Flat Ernie
    Tech Editor

    Joe Abbin has flowed them - no appreciable difference. Something to remember about the Harley K-motors is the valve inclination is much different and the port configuration is radically different than Henry's bent 8.

    A standard .100" relief that follows the contour of the combustion chamber in the head - not the gasket - is good for 7-15% increased flow regardless of head used.
     
  3. jetmek
    Joined: Jan 12, 2006
    Posts: 1,847

    jetmek
    Member

    thanks ernie...i guess the idea was to retain some material to keep compression up while improving intake flow...
     
  4. A Chopped Coupe
    Joined: Mar 2, 2004
    Posts: 1,133

    A Chopped Coupe
    Member

    The one thing I found out after starting this flathead quest, is that talking to 10 different people about building a bent8 will usually give you 7/8 different answers.
    I started my quest with the late Rod Furtado, talked to Barney Navarro, "Ole Ron", and others before I started my own direction. Rod Furtado had built a number of impressive flathead motors and I talked him into step relieving my 8BA block. He told me he had always wanted to..................so he did a ruff cut of .050 on the exhaust and .100 on the intake.
    I relieved the block to the combustion chamber only, not the gasket. I took the intake side to .125 and the exhaust to .075. I will mention here that I started wanting a tri-power motor that would develop 250HP.............but then changed my mind and put a Joe Abbin small 141 Weiand set up and am hoping for 300HP. I only say this because I will running the motor on the street (91 or less octane) with about 7.4 to 1 compression, and I wasn't worried about lossing any compression.
    Anyway, the motor is going together and it will be interesting to see what kind of numbers she will put out...................and how relieable it will be in a street driven Coupe.
    As Flat Ernie mentioned, I believe it will increase the intake side considerably and because of the type of head and placement of the spark plug along with larger intake valves should give
    me what I am aiming for..................we will see.
    One last comment, Rod very seldom let a bent8 block leave his shop without at least relieving the block like Ford did on some of its truck blocks............Rod believed this increased the area (cross section) where flatheads are prone to cracking due to high heat. If you look at a none relieved block the valve pocket and cylinder wall come together and form a point..................very little metal at that point.............and if the block gets hot enough this is where it will seperate...............relieving the block actually relieves stress at this point................
     

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  5. Ole don
    Joined: Dec 16, 2005
    Posts: 2,915

    Ole don
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    Very nice work. It should be a killer motor.
     
  6. banjorear
    Joined: Jul 30, 2004
    Posts: 3,772

    banjorear
    ALLIANCE MEMBER

    Very true. If Henry only went with 20 or less heads bolts, it would be a different ball game.
     
  7. banjorear
    Joined: Jul 30, 2004
    Posts: 3,772

    banjorear
    ALLIANCE MEMBER


    Agreed- AChoppedCoupe has done his homework. I'd wouldn't want to be a tuner car pulling up next him at a stop light.
     
  8. Flat Ernie
    Joined: Jun 5, 2002
    Posts: 8,410

    Flat Ernie
    Tech Editor

    On a "standard" 276" flatty (.125" over 4" crank), a .125" relief only loses 0.3 CR over non-relieved. Not a whole lot in the grand scheme of things & it's my personal opinion that the increased flow more than offsets the slightly lowered CR.
     
  9. A Chopped Coupe
    Joined: Mar 2, 2004
    Posts: 1,133

    A Chopped Coupe
    Member

    The most important thing in building a motor is picking everything from the carb to the oil pan....................and planing on making sure everything works together. Many years of drag racing taught me that without a lot of thought...............putting together a motor that is reliable and still makes great torque/HP is not easy................but when it all comes together it's like night and day. On the street it isn't any different...........and making an extra 5/10HP is something you can feel in the "seat-of-your-pants". I believe that relieving the block will give you at least this amount on a mild motor.............IMHO
    The heads I have were specificially designed for the valves, pistons, (and are made of 6061 alloy which will allow me to firmly attach them to the block via ARP studs and a torque setting of 65lb ft) and relief in the block. The cam (an Isky 400jr) is a starting point............and as "Ole Ron" told me...........if it doesn't work you can always put a different one in there, although it's a little more work than a SBC/SBF. So.............it boils down to what you want out of the motor you building and how you plan to drive it.
    Mine is a 289ci (4.125 stroke X 3.342 bore) and will never see the other side of 5krpm, but I have a 6/7psi pulley, 8/9psi pulley and another one with just a little more boost.....I will try them all..................part of the reason for going with HBeam rods and steel main caps with ARP studs along with lightning the crank and rotating assembly........................which is just part of blueprinting a motor.
    There are a lot of things I would like to try on my next motor(s), like using an external oil pump, redesigning the oil pan, and even trying a set of 180 headers.................working on flatheads is just a lot of fun!!!!!
     

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  10. Flat Ernie
    Joined: Jun 5, 2002
    Posts: 8,410

    Flat Ernie
    Tech Editor

    I assume you'll be running an MSD-BTM or something similar with that much boost...
     
  11. A Chopped Coupe
    Joined: Mar 2, 2004
    Posts: 1,133

    A Chopped Coupe
    Member

    Flat Ernie,

    I've got two ignition systems, one is a Mag and yes the other is an MSD 6BTM with boost retard.
    I think I'll start out with the mag because the MSD is big enough I will have to add another pulley for the serpintine belt to miss the cap.
    We will see.....................
     

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  12. Flat Ernie
    Joined: Jun 5, 2002
    Posts: 8,410

    Flat Ernie
    Tech Editor

    I hate to use "fake" stuff, but Speedway has that mag look-a-like that's really an electronic ignition - you could use that to trigger the MSD.

    For that matter, you can use an old Mallory to trigger the MSD box...should clear your belt.

    What heads are those? Look kind of like those "big boy" heads, but w/o the logo...

    Love the fomoco hoses! ;)
     
  13. A Chopped Coupe
    Joined: Mar 2, 2004
    Posts: 1,133

    A Chopped Coupe
    Member

    Flat Ernie,

    I hate the "fake" stuff also. Since Joe Hunt makes the Mag look alike I could have them make a "fake" mag (plus I've already made an extra pulley to re-route the belt away fromt he MSD cap), but I ran one on the street some,,,,,,,,,,,,,,well............a long time ago in a 56 Chevy. I really like the idea of being able to spin the motor (get everything out of the cylinder) then hit the mag switch and fire it up..........I think it helps on a cold motor.
    The heads are Norman Frick 2 piece type. Really nice, and made from 6061 alloy and I will be screwing them down with about 65lb ft (to the studs).
    Here are some pictures;
     

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  14. Flat Ernie
    Joined: Jun 5, 2002
    Posts: 8,410

    Flat Ernie
    Tech Editor

    You can do that with most any ignition if you wanted to wire it up that way...and it's probably not a bad idea on a hi-comp engine anyway. Don't know if it helps so much to get things out of the cylinder as it ensures all cylinders have a fresh air/fuel charge before lighting the mix! :D
    Thanks for the pics - interesting back cut behind the valve pockets.
     
  15. flatoz
    Joined: May 11, 2003
    Posts: 3,103

    flatoz
    Member

    interesting,

    I dont have a msd bmt, and have seen 12lbs boost into my motor and it hasnt rattled. it did the other day but I was getting into it a bit. However rat bastad has one ( btm) and he thinks its pretty good. I have a mag for my motor and am thinking about trying to run that on the street. have it ready to go, but am daily driving the car at the moment so dont want to play with it too much incase I do something I cant undo before the weekend it over.

    the mag will probably never be as good as the electronic for spark but the cool look and knowing you have a mag all but makes up for it.
     
  16. Flat Ernie
    Joined: Jun 5, 2002
    Posts: 8,410

    Flat Ernie
    Tech Editor

    I would highly recommend some sort of timing retard when running any boost over about 6-7psi...

    You may not be able to hear the rattling when you're on it - the damage can happen quickly.
     
  17. A Chopped Coupe
    Joined: Mar 2, 2004
    Posts: 1,133

    A Chopped Coupe
    Member

    I also recommend................very highly...............that you get some type of boost control or lower the boost under 7psi. Just because you can't hear it..........doesn't mean "its not happening".
    Had a 97 Mustang Cobra with KennyBell charger at 12psi.................put a foot to the floor once too often.............broke ring lands in number 4 and 6 cylinders (and never heard any pinging what-so-ever). The car ran fine for a while with the lands broken and just acted like it was down on power............was a very costly mistake!!!!!
     

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