Top speed of an L-head 134

Discussion in 'Flat Fender Tech' started by Old Doug, Jan 24, 2012.

  1. Jan 24, 2012
    Old Doug

    Old Doug Member

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    I would like to know how fast can a bone stock 47 Cj2a go? I had nine up to 41 going down hill is this right?
     
    Last edited by a moderator: Jan 26, 2012
  2. Jan 26, 2012
    Gwillys

    Gwillys 1953 CJ3B

    Southington, Ct
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    Re: Yop speed of an L-head 134

    I guess it would depend on how worn the engine is. Mileage and ring condition plays a big part. Ive had my used f-head (similar) with unknown mileage up to 55 on flat ground and it has a cracked block, leaking coolant into the cylinders. The thing that really worried me was how loud the trans/transfer case wined.

    I wouldnt take yours on a highway without an overdrive. Even then dont expect to go much faster than 60.

    Curious to hear what others say.
     
  3. Jan 28, 2012
    sterlclan

    sterlclan Member Sponsor

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    Re: Yop speed of an L-head 134

    my buddy has a m38a1 with pinto power......top speed 56 mph limiting factor gears....
     
  4. Jan 28, 2012
    Alex V.

    Alex V. Member

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    Re: Yop speed of an L-head 134

    FWIW, one source I've seen said the redline is 3,200 RPM, but it's not a good idea to sustain more than 2,800 for long.
     
  5. Jan 28, 2012
    Patrick

    Patrick Super Moderator Staff Member Sponsor

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    Re: Yop speed of an L-head 134

    That wouldn't be accurate. The military tested them @4,000 sustained for some number of hours. First hand, my Brother used run his @4K all the time. There's no way you could pull hills if you didn't rev it that high.
     
  6. Jan 28, 2012
    Glenn

    Glenn Kinda grumpy old man Staff Member Sponsor

    Apopka, Fl
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    Re: Yop speed of an L-head 134

    I believe all flatfenders have a dash tag that states top speed in 3rd gear is 60 mph. Bottom line is that's how fast it should be able to go.
     
  7. Jan 28, 2012
    oldtime

    oldtime oldtime

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    Re: Yop speed of an L-head 134

    Various crankshaft velocities for the L-134 Go-Devil
    Speeds with 6.00 x 16" tires and 5.38 final drive ratio

    Maximum RPM = 4000 = 61 MPH
    Maximum Sustained RPM = 3200 = 49 MPH
    Medium Sustained RPM = 2600 = 40 MPH
    Maximum Torque RPM = 2000 = 31 MPH

    The maximum sustained crankshaft velocity is the fastest RPM providing reasonable service life.
    The medium sustained crankshaft velocity is the ideal velocity for hiway use.
    The maximum torque output RPM is the most efficient crankshaft velocity.
    Providing the best MPG economy excluding wind drag.
     
  8. Jan 28, 2012
    garage gnome

    garage gnome Rust polisher Sponsor

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    Re: Yop speed of an L-head 134

    I believe the dash tag speed data came from the MBs which had 4.88s or some axle ratio like that, IIRC.
     
  9. Jan 28, 2012
    Glenn

    Glenn Kinda grumpy old man Staff Member Sponsor

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    Re: Yop speed of an L-head 134

    I would have to assume they got the speed numbers matched with the 5.38 gears and size tires as oldtime stated. Isn't that how yours is setup?
     
  10. Jan 28, 2012
    garage gnome

    garage gnome Rust polisher Sponsor

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    Re: Yop speed of an L-head 134

    I did a little test one day and I couldn't reach the number listed on my dash tag. As far as I know, MB's have the same numbers listed on their tags. JMO

    On the CJ2A page, a member (jpet) conducted a similar test, but it was about OD vs. no OD. I think he got up to about the 50 MPH range without shifting into OD and 60ish with OD (F Bill?). Windshield down + OD was a whole other story. He got up to 70 with his 2A.
     
  11. Feb 8, 2012
    86cj7

    86cj7 New Member

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    Re: Yop speed of an L-head 134

    my 46 will top out at 35mph.
    the 34x9.5 swampers do not help but it looks cool
     
  12. Feb 15, 2012
    1960willyscj5

    1960willyscj5 Well-Known Member

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    Re: Yop speed of an L-head 134

    If you are running tires bigger than what came on it new, and you haven't had the speedometer reset, you may be going as much as 10 mph faster than indicated.

    Take your GPS along and see how the speeds match or don't match.
     
  13. Feb 17, 2012
    86cj7

    86cj7 New Member

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    Re: Yop speed of an L-head 134

    my speedo just kinda bounces a little bit. when i recorded my supersonic high speed run of 35mph my dad was behind me in his grandcherokee trying to keep up
     
  14. Feb 18, 2012
    windyhill

    windyhill Sponsor Sponsor

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    Re: Yop speed of an L-head 134

    bone stock 3A likes 50mph have gone 65 on the down hill. An overdrive doesn't really add any more speed just drops the rpms, the L head doesn't have enough poop to push it any faster then around 60 even with od.
     
  15. Feb 18, 2012
    1960willyscj5

    1960willyscj5 Well-Known Member

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    Re: Yop speed of an L-head 134

    The nice thing about the flat head engines is they can be hopped up to produce around 100 hp. The F-Head on the other hand, is stuck at at the most 75 horses.
     
  16. Feb 19, 2012
    silverbullet72tnt

    silverbullet72tnt Member

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    Re: Yop speed of an L-head 134

    Hopped up? with what parts and how? Very interested in a bit more snot out of the old flathead
     
  17. Feb 19, 2012
    nickmil

    nickmil Super Moderator Staff Member Sponsor

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    Can you explain how? And why can't the F head be hopped up too? The intake flows better.


    Sent from my iPhone using Tapatalk
     
  18. Feb 19, 2012
    Patrick

    Patrick Super Moderator Staff Member Sponsor

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    Re: Yop speed of an L-head 134

    That's the first I've heard that..
     
  19. Feb 19, 2012
    w3srl

    w3srl Curmudgeon-in-training Staff Member Sponsor

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    Re: Yop speed of an L-head 134

    I'd be interested in hearing about that.
     
  20. Feb 22, 2012
    1960willyscj5

    1960willyscj5 Well-Known Member

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    Re: Yop speed of an L-head 134

    You can shave the flat-head and raise the compression a bunch, which will increase the horsepower.
    Some other things.
    Used to be after market heads available with smaller quench areas from some one like Offenhauser for the Willys flat-head 4 in the Coupe that was the same as the flat-head in the Jeep. Some were supercharged.
    That kind of thing.
     

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