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Technical Question for the Flathead guys!

Discussion in 'Traditional Hot Rods' started by 19-c, Oct 11, 2018.

  1. 19-c
    Joined: Jun 15, 2009
    Posts: 963


    Question? What can one expect for horsepower increase when adding Heads and Dual carbs to a stock 8ba? I understand every situation is unique but no one has every been able to answer this question even in the broadest of terms. 5hp? 10hp? More?
    FlatheadRods likes this.
  2. Cool heads and a dual intake add at least 75 to 100 Visual Horsepower. as for actual, probably not as much as we would like it too.
  3. Petejoe
    Joined: Nov 27, 2002
    Posts: 9,656

    from Zoar, Ohio

    I’d guess 5-10 hp. Hardly noticeable.
    Agree on the cool factor.
    FlatheadRods, LOU WELLS and 3340 like this.
  4. 19-c
    Joined: Jun 15, 2009
    Posts: 963


    flatheads have never been praised for their $ to Hp ratio haha
    expavr likes this.
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  5. Kiwi 4d
    Joined: Sep 16, 2006
    Posts: 2,274

    Kiwi 4d

    LOU WELLS, 3340 and 48fordnut like this.
  6. alchemy
    Joined: Sep 27, 2002
    Posts: 12,934


    If you paint the block red it will also increase the HP.
  7. 19-c
    Joined: Jun 15, 2009
    Posts: 963


    I’ve seen it many times lol
  8. RMR&C
    Joined: Dec 26, 2009
    Posts: 2,890

    from NW Montana

    May decrease hp if you don't swap the distributor and/or know how to tune the carbs.
    deucemac, chiro, LOU WELLS and 3 others like this.
  9. 19-c
    Joined: Jun 15, 2009
    Posts: 963


    I had a 39 flathead with a Mallory electronic ignition and really liked it! I felt it really brought that motor around and was also very reliable.
  10. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 4,550

    Bandit Billy

    It worked for me! Orange slows motors down.
    To answer the OP's question, Aluminum heads can increase the compression, add cooling capability as aluminum displaces heat better than iron, which allows for more timing without more heat which is already an issue. Internally there are changes which are more costly but needed if you really want to warm one up. Sky's the limit I guess, my HP cost ended up at $46.75 per HP. Hardly a bargain. A SBC mildly warmed up is probably $17.14 per HP by comparison. Cool points though...that's a whole other enchilada.
    Jet96, LOU WELLS, 3340 and 1 other person like this.
  11. 19-c
    Joined: Jun 15, 2009
    Posts: 963


    Wow really some great info here great set up in your roadster Billy I also really liked the link that Kiwi posted from H&H some excellent data in it!
  12. sloppy jalopies
    Joined: Jun 29, 2015
    Posts: 2,525

    sloppy jalopies

    a '51 Merc motor had 112 horse... so adding 10 hp is almost a 10% increase...
    belt the extra pop will feel goooood !
  13. nutrocker
    Joined: Jan 12, 2007
    Posts: 298


    My flathead story.
    I started with a completely stock french motor. It had a 4” crank and stock cam which was .324” lift.
    I fitted stock Merc iron heads, Chevy points dizzy, a set of home made headers and a triple carb manifold with 3 x 1-3/4” SU carbs. First run on the dyno gave me 87hp. A bit of tuning of the carbs and timing and I came out with 113hp.
    A while later I fitted aluminium heads but never got any dyno numbers, but it didn’t feel any different.
    Later I converted the heads to twin plug and fitted a .395” lift cam. Bit of work on the dyno and I had 149hp. Blew up the motor. Rebuilt it with the same twin plug heads, .395” lift cam but added lots of porting, 3-3/8” pistons, 4-1/4” stroker crank, 1.6” valves etc. 198hp and 400 ft lbs of torque.
    So, for me the heads didn’t make much of a difference, but everything else did.
    bundybiker and Surfcityrocker like this.
  14. kbgreen
    Joined: Jan 12, 2014
    Posts: 308


    Doesn't that make it a Chevy flathead though?
  15. 19-c
    Joined: Jun 15, 2009
    Posts: 963


    Thanks KB some great inform to know! Carbs and timing are more of a factor than heads but even with that the change is minimal
  16. Pete1
    Joined: Aug 23, 2004
    Posts: 1,527

    from Wa.

    On one particular bone stock 239 with 40K miles, an Edelbrock Super manifold with 2 Stromberg 48's, Edelbrock 9 to 1 heads and headers, gained 23 hp. Started with 78. Year 1954.
  17. 36 Penny Coupe
    Joined: Jan 7, 2014
    Posts: 144

    36 Penny Coupe
    from VA

    Here is a real world answer to your question I recently completed and started driving my coupe around town. My car has a 1950 Ford Flathead in a 1936 Ford 5 window. Egge dome top pistons. New Stromberg 97 dual carbs and Edelbrock 74cc high lift heads. Adjustable lifters. Fenton headers with custom high flow dual exhaust. First of all I have no idea of the actual horsepower. I honestly don’t care. What I do know is that the car feels strong and gets up to speed quickly. I’m running a 3 speed top loader that shifts well. For me it has plenty of power and fun to drive. Definitely a way cool weekly driver to work. [​IMG][​IMG]

    Sent from my iPhone using H.A.M.B.
    Jet96, R A Wrench and Pinstriper40 like this.
  18. 19-c
    Joined: Jun 15, 2009
    Posts: 963


    I love hearing about everyone’s experiences and real life scenarios! Thanks for the input everyone. Keep chiming in with your stories! Thanks!
  19. Bursonaw
    Joined: Jun 19, 2011
    Posts: 68


    The book Flathead Facts has a lot of great information on this subject. The author takes a stock motor and runs it on a dynamometer to test the power increases with different flathead speed equipment.

    In short the book claims noticeable increases with heads and some intake manifolds over stock.


    Sent from my iPad using Tapatalk
  20. choffman41
    Joined: Oct 30, 2012
    Posts: 2,113


    In 1958 I was driving a '40 coupe to school with a bone stock flattie. I put aluminum heads and 3X2 97's on it. I don't know if it went slower, but I doubt it went faster.
    RMR&C likes this.
  21. Pinstriper40
    Joined: Sep 24, 2007
    Posts: 3,103


    My '40 sedan in my avatar has a Merc crank, is bored to 3 5/16", Eddie Meyer high rise 2x2, Mallory ignition, an Isky 77B cam, dual exhaust and Edelbrock heads. I would say it produces somewhere around 150-170 HP. Dual carbs, dual exhaust, ignition and .010 shaved off the stock head surface will bump you up to 135 HP pretty easily, depending on which intake you run. According to Joe Abbin's book, a Thickstun 2x2 isn't a good performer, and the easily found Offenhauser or Edelbrock Super Dual intakes are two of the better intakes to use.
  22. Drbrown
    Joined: Nov 6, 2013
    Posts: 17


    Go to the Ford Barn and consult "Ol'Ron" who's been racing all his life and wrote the book. News is out - headers don't increase HP unless your existing one's are clogged with carbon, and unless you leave the hood off for people to see some chrome, it won't go faster.
  23. chiro
    Joined: Jun 23, 2008
    Posts: 677


    My experience (which is limited since it's my first flat motor): Rebuilt 59AB of unknown provenance, but probably really low miles as no ridge in cylinders and honing marks still clearly visible in cylinder bores when I got it. Unknown cam but probably stock, .030 over bore (stamped on top of pistons). I put 9:1 edelbrock heads (swap meet find), Edmunds custom 2-pot manifold, Holley 94 carbs linked together-NOT progressive linkage on it. First fire up showed 150 psi in all cylinders. Took a LOT of fiddling to get it to run the way I wanted it to. Had to rebuild my carbs again (buy a cheap ultrasonic cleaner-they work amazingly well). Had to put smaller jets in (twice) and smaller power valves (3.5 now). Up till then it ran way too rich. Running 46 jets now (stock jets are 51, I believe). Bubba's point distributor, solid core wires, NGK B6L plugs set at .025. Mechanical stock fuel pump with pressure regulated to 2 lbs. Runs out very well now and is a shitload of fun. I am always the ONLY flat motor at any cruise night. Nobody goes, "Oooh!" at a small block Chevy.
    Last edited: Nov 25, 2018
    Jet96 likes this.

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