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Hot Rods How Much Horsepower Does The Average Flathead Make

Discussion in 'The Hokey Ass Message Board' started by Speed Gems, Oct 19, 2019.

  1. Speed Gems
    Joined: Jul 17, 2012
    Posts: 2,480

    Speed Gems

    Last edited: Oct 19, 2019
    Boden likes this.
  2. Mr48chev
    Joined: Dec 28, 2007
    Posts: 26,096


    Those numbers are probably locked in the safes of those who have them. Most don't build flatheads for dyno numbers. If mine puts out 30 more hp than it was rated at stock when I get it done I'd be plum tickled. I've got more money tied up in it than any other engine I have ever owned no matter what's year dollars you compare.
    Even then that isn't a lot of actual cash but I have always had reasonably plain and simple engines before. In today's $$ the 327 in my 57 Chevy Panel would no doubt be the most expensive as it would run close to 4 K to duplicate it now.
  3. Tim
    Joined: Mar 2, 2001
    Posts: 10,435

    from Raytown Mo

    Generaly a “hot” Flathead is around 150 hp unless you have an obscene amount of time/money in it. Then your probably telling tall tales of 250 hp.

    With a blower I’ve seen them street able around 300hp I bet @Bandit Billy has numbers for his gem
    stillrunners and Speed Gems like this.
  4. Marty Strode
    Joined: Apr 28, 2011
    Posts: 4,272

    Marty Strode

    Tim is probably close at 150, this 292 incher made 225. Narvaro Hi-Dome heads, Isky 404A camshaft, Vertex Mag, lots of port work. Roadster Show 1.jpg
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  5. ramblin dan
    Joined: Apr 16, 2018
    Posts: 1,803

    ramblin dan

    My grandfather used to say a flathead was only good for making hot water.
  6. Baumi
    Joined: Jan 28, 2003
    Posts: 2,235


    Hahahaa, that´s a good one.
    Boden and lothiandon1940 like this.
  7. Marty Strode
    Joined: Apr 28, 2011
    Posts: 4,272

    Marty Strode

    I take it your Grandfather never heard of John Bradley.
    Boden likes this.
  8. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 4,844


    Which flathead family? Ford, Cadillac, Hudson, Lincoln, Briggs & Stratton, etc?
    Last edited: Oct 19, 2019
    williebill, Deuces and Boden like this.
  9. Boden
    Joined: Oct 10, 2018
    Posts: 567


    Merc crank,3/4 cam,64cc heads,bored a little .030-.060, 2 or 3 deuces stock valves. I would say around 155-180. Like my boss said. He built two motors exactly the same down to the thousandths of an inch and brands and everything. He said one made 10 more hp than the other. But I would say I’m in the ballpark. That’s around what my motor makes I think. Because that is my exact list of parts. Haha. Pretty much what everyone does for a street flathead.

    Sent from my iPhone using H.A.M.B.
  10. flatford39
    Joined: Dec 3, 2006
    Posts: 2,389


    Without walking to the shop and getting a Motors Manual I remember them being listed at 100HP from the factory. And that was the Merc motors. You may get that to 125 with some bolt on stuff but I doubt it. It takes a lot to get HP out of a Ford flathead.
  11. Boden
    Joined: Oct 10, 2018
    Posts: 567


    Nope. The merc motors from 49-51 was 110hp and the 52-53 merc motors were rated at 125hp due to carb and compression. Ford from 49-51 was 100hp and ford from 52-53 was 110hp. Due to van pelt sales and the manuals

    Sent from my iPhone using H.A.M.B.
    Speed Gems likes this.
  12. John Lawson's book on flathead building and respective dyno numbers using different parts combinations is real world info. Search on the Fordbarn for his address. His handle on there is JWL. He's in Fitzgerald, GA.
    Speed Gems and Texas Webb like this.
  13. Buy John Lawson's book,great information and facts..... real info.
    Speed Gems likes this.
  14. Deuces
    Joined: Nov 3, 2009
    Posts: 17,982

    from Michigan

    Nice motor, but not enough.....
  15. southcross2631
    Joined: Jan 20, 2013
    Posts: 3,207


    Barely enough to pull a sick whore off a piss pot. But they sound good doing it.
    My friend spent an obscene amount of money to make over 200 hp.
  16. flat 39
    Joined: Dec 31, 2007
    Posts: 216

    flat 39

    My 265 cu in has EAB heads, dual Holley 94's and a Schnider F260 cam. using one of the drag strip / horsepower calculaters it makes about 125 HP.
    stillrunners and Boden like this.
  17. Gman0046
    Joined: Jul 24, 2005
    Posts: 5,768


    Over the years I've had several Flathead powered cars none of which provided the performance I'm satisfied with.
    Desoto291Hemi likes this.
  18. rusty rocket
    Joined: Oct 30, 2011
    Posts: 3,615

    rusty rocket

    I'm thinking you don't build a flathead for the h.p. you build it for the nostalgia and the style of build you are doing.
    When I set out to build my 26 T modified I was bound determined that I was going to use a 2300 Ford 4 cylinder and a hood to cover it up. The flathead that's in the car sort of fell in my lap and it's looks determined the style of the build I went with(it was the best move of the whole build)and I get more comments on the motor than anything. I don't give a rats ass about H. P. Because the car is so small it feels like your going 100 when your going 50.
    Desoto291Hemi, ABONES and 56shoebox like this.
  19. Tim
    Joined: Mar 2, 2001
    Posts: 10,435

    from Raytown Mo

    I feel like in a light car with the right gears they are just fine. But if you want to stick an auto behind it with highway gears in it you may as well be trying to push it.

    T-5 and 4:11’s in a 2000 pound car and you’ll have plenty of fun
  20. Russco
    Joined: Nov 27, 2005
    Posts: 4,074

    from Central IL

    Since they are not high winding they are not going to ever make a lot of “HP” they do have a great torque curve. I would suspect very few of them out there make over 200. I built a pretty nice 286 a few years back with balanced aftermarket crank and rods, nice Ross pistons. An old 1007B grind from Pete1, EAB heads that had been worked over with fire slots ETC. a Mallory Dist that Jim Linder set up with a HEI inside. Set timing at 22* total. And a 2 pot Edmunds intake with nicely tuned 94’s. It ran great! It made great low and midrange power like crazy but I never dyno’ed it I’d bet it was about 180 or so at best.
    stillrunners likes this.
  21. drtrcrV-8
    Joined: Jan 6, 2013
    Posts: 1,222


    Not enough for some, & Not enough for others! As long as it gets down the road decently & looks good while doing so, who really cares???
  22. dan c
    Joined: Jan 30, 2012
    Posts: 1,950

    dan c

    don garlits said he switched to hemis when he saw an ad touting its 180 horsepower. that's the same as his modified flathead dragster engine!
    Tim likes this.
  23. ol-nobull
    Joined: Oct 16, 2013
    Posts: 1,333


    Hi. No need to dyno mine to verify mine but the factory specs on my Plymouth 218 CI six flathead show the brake HP to be 97 @ 3600 rpm and taxable HP at 29.35. Iam getting a bit more than that with it bored 0.030 over when overhauled. Must be enough as it gets down the Hwy quite well for me.
    stillrunners, Desoto291Hemi and Boden like this.
  24. anthony myrick
    Joined: Sep 4, 2009
    Posts: 5,042

    anthony myrick

    You can spend 10k to get the same hp of a stock 350
    But dang they look and sound good.
  25. Elcohaulic
    Joined: Dec 27, 2017
    Posts: 694


    200. I heard the first car to make it into the 10s was flat head powered..
  26. Shamus
    Joined: Jul 20, 2005
    Posts: 1,130

    from NC

    Not about horsepower - it's about "coolness"!!

  27. Boden
    Joined: Oct 10, 2018
    Posts: 567


    That’s not much bigger. If that’s all that’s done it’s maybe 5 more hp

    Sent from my iPhone using H.A.M.B.
  28. Pete1
    Joined: Aug 23, 2004
    Posts: 1,680

    from Wa.

    Street with GOOD DRIVABILITY, 175.
    All out race with blower and 100% nitro, 800.
    All out race with blower and gas, 500+.
    All out race naturally aspirated on alcohol, 400+.

    An interesting side note is, John Lawson in researching his book, "Flathead Facts", found that a STOCK 239 flathead would not make the rated 100 hp. on the dyno.
    dan c and stillrunners like this.
  29. Flathead Dave
    Joined: Mar 21, 2014
    Posts: 2,525

    Flathead Dave
    from So. Cal.

    I guess it depends on if you are running stock or built. My factory stock 1951 239, 8BA is supposed to put out 100hp. I'll never put it on a dyno si I guess I'll never really know for sure.
    As for the 60hp flathead ..probably around 60hp...etc.
    Desoto291Hemi likes this.
  30. old school rodder
    Joined: Dec 12, 2012
    Posts: 161

    old school rodder

    My flathead dyno'd at 173, 220 torque. Nothing exotic, 4-barrel Offy intake, 4"crank,3-5/16 bore, new Navarro heads. Very solid running motor. About to bolt on a Weiand 144, with another$3K investment, should get up around 250hp. The 173 is Rock solid verified. I'm thinking that's the reasonable limit on gas.

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