Top speed of an L-head 134

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

  1. Mar 6, 2012
    JeepPower

    JeepPower Hopeless Gearhead

    Fort Mill, SC
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    amen!

    my '5 was my ride in highschool-- with no $$ for the O.D., the only tickets I got were for failed/no inspection! :D
     
  2. Mar 8, 2012
    DoubleBit

    DoubleBit Member

    East of Auburn, CA
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    This such a subjective question/subject... These jeeps are so old there aren't many stock ones left let alone stock and in solid mechanical condition... The world was a different place in the 1940s... Top speeds were certainly high for some cars on the freeways, but rural America was a big place back then and you could drive for hours at 35-40ish mph and it wasn't a problem... Try it today, you'll be moving over a lot to let the Subarus etcetera fly by at 70+ on gravel roads...
    Darn I started to rant, please forgive me...
    It's a matter a power vs gears vs gravity/drag, and what your sense of machanical mercy will allow... My old MB with a t90, 5.38 gears, and F-head tops out around 50-55 depending on head winds and such... BTW, the lower gears actually increased my abillity to pull top speed in high gear... With the ol' 4.88s, it was only possible with a tail wind or slight down grade...
    FWIW, have fun, run it clean as you can get it and do not expect speed out of it... Most of my friends refer to my old jeep as a Billy Goat which is fitting, it's tough, small, agile, not particularly pretty, and will go places that astound most folks... (notice fast, was not one of the attributes?)...
     
  3. Mar 8, 2012
    BlueComet

    BlueComet 1962 JEEP CJ-5

    Montrose, Colorado
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    I think this is an interesting discussion, as I have an old L-head in my CJ-5. It has always been underpowered, but I've tried to live with it. Often debated whether to do an engine swap, but the money side of anything but an F-head has always discouraged me.

    So, if an F-head were swapped in, do you think there would be a noticable difference? What kind of power do you think an F-head would generate with headers and a Weber carb? 90hp? Would it be smarter to try to hop up the L-head instead? I heard some ideas here that I've not heard before.

    I wouldn't need to go over about 55 or 60, but I'm more concerned about higher elevation driving here in Colorado. We have some great trails, but many are at 7000 or 8000 feet or even a little more. I've really struggled up some grades in low range.
     
    Last edited: Mar 8, 2012
  4. Mar 8, 2012
    JeffsJeep04

    JeffsJeep04 Member

    Menomonie, WI
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    I've only driven an L head about 20 feet to prove to a buddy that it wasn't stuck in 4wd, it just needed to be carefully drifted out. That being said, I feel no real lack of power with my F head...definitely wish I had a lower 1st gear so I didn't have to slip the clutch so much, but once she's rolling it's plenty strong.
     
  5. Mar 9, 2012
    jeep2003

    jeep2003 Active Member

    vestal ny
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    mine does 55 pretty easy power really isnt a problem just runs out of gearing and it gets pretty windy and scary but its on 35" tires
     
  6. Mar 10, 2012
    1960willyscj5

    1960willyscj5 Well-Known Member

    Mesa, Arizona
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    If you have a CJ5 with an L-Head (flathead) engine in it, somebody already swapped the engines. If the L-head is stock, then putting in an F-Head will give you 15 more horsepower. And it is a direct bolt in, because the F-head and L-head share the same block.
     
  7. Mar 11, 2012
    oldtime

    oldtime oldtime

    St. Charles,...
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    Absolutely not !
     
  8. Mar 13, 2012
    jwjeep60

    jwjeep60 in process

    Sedalia Mo.
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    a slight difference, i think along the head gasket area...
    as far as F-head in a factory L-head jeep, I think there is a hood clearance issue... i think ;)

    the F-head will bolt onto a L-block just as a vortec head will bolt onto a 327 block it can be done... but it is not exactly bolt on. and some work between body mounts and carb setups will cover those 15 draft horses.


    anyway a Cow = a Bull
    they both moo, and cook over a grill. don't milk the bull and you will be ok.
    otherwise, you will have some trouble making it work right.
     
    Last edited: Mar 13, 2012
  9. Mar 13, 2012
    nickmil

    nickmil Super Moderator Staff Member Sponsor

    Happy Valley, OR
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    And the fact the intake valves are in the head in an F head and they are in the block in an L head. Just a minor difference......


    Sent from my iPhone using Tapatalk
     
  10. Mar 13, 2012
    jpflat2a

    jpflat2a what's that noise?

    Riverside CA
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    If I were you I'd keep my eyes open for an F-Head; the YF can be adjusted for high altitude if you can locate the correct metering rod for the carb; that and advancing the timing about 5 degrees will help at high elevation.
    My F-Head ran fine at 10,000' elevation; it wasn't a rocket by any means but I always had plenty of power, more so in low range. My diffs are 5:38s so maybe that's the difference. Highway driving was easy at 55-60mph, grades slower but the OD made it doable. I drove the Jeep to Colorado from Calif with the F4 twice.
    Since you don't drive fast on a lot of those passes anyway, low range can be your friend for compression braking as well.
     
  11. Mar 13, 2012
    JeepPower

    JeepPower Hopeless Gearhead

    Fort Mill, SC
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    awesome. a man after my own heart--
     
  12. Mar 13, 2012
    oldtime

    oldtime oldtime

    St. Charles,...
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    Re: Yop speed of an L-head 134

    Back to the original question.....
    Back in the 1970's I restored a nearly stock standard CJ-2A for my daily driver. (Go-Devil)
    If you recall in the late 70's and early 80's the national speed limit was 55 MPH.
    I drove that Jeep from St Louis out to Death Valley where I lived for a spell.
    After driving the 2A through most of southern California I headed back about one year later.
    My average speed enroute was about 50 MPH without an O.D. unit.

    Wasn't too long after that when the speed limit went back up.
    I wanted and needed more power for my daily driver.
    So in 1984 I restored an optional stock CJ-3B. (Hurricane)
    The standard Hurricane only has 12 more HP than the Go-Devil , BUT...
    When your engine is that low on HP; 12 is a large percentage of increase.
    That said the O.D. is absolutely the single best addition to make a flatty roadworthy.

    The ONLY thing I miss about the CJ-2A is the somewhat lower hood.
    Otherwise the standard 3B wins hands down over the other flatties in virtually every respect.

    I currently drive a 1962 stock standard CJ-3B as my one and only daily driver.
    I feel that it has just enough HP to get by with for use on the interstate.
    Yes It's marginal. Refer to Jim Allen's Jeep torque formula.
    Thousands of miles of real world experience indicates that.....
    The Hurricane with 25% O.D. having 5.38 final drive on narrow 29.5" tires is good for speeds from 45 to 65 MPH maximum sustained speed.
     
  13. Mar 13, 2012
    jeep2003

    jeep2003 Active Member

    vestal ny
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    i heard a F head fits in a 2a especially with a solex
     
  14. Mar 13, 2012
    garage gnome

    garage gnome Rust polisher Sponsor

    Western MA
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    :shrug:

    I like my Lhead in my '53. It gets me where I'm going and is pretty good on gas.
     
  15. Mar 14, 2012
    1960willyscj5

    1960willyscj5 Well-Known Member

    Mesa, Arizona
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    F-Head will fit into a 2A if you cut a hole in the hood to clear the carb top. That includes the Solex cabs too. They are taller, I believe. Don't know first hand on the height, though. I am still running the original carb on mine. And put an air scoop around the aircleaner on top of the carb. Although I have seen the hood with just a big bubble in that spot, too.
     
  16. Mar 14, 2012
    nickmil

    nickmil Super Moderator Staff Member Sponsor

    Happy Valley, OR
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    My understanding is if you use the carb from a falcon with the 170 you can fit the Fhead in a 2a/3a without cutting the hood. I haven't done it myself but I've heard that from several different sources. I think it may have been discussed here so a search may show some info.


    Sent from my iPhone using Tapatalk
     
  17. Mar 14, 2012
    Bill F

    Bill F Finally running

    Hillsboro NH
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    My stock m38 will cruise at 50mph it however does seem to like 45 better. I have had it to 60mph for a short time but wouldnt do it often. The m38 is the heaviest flatfender jeep.
     
  18. Mar 17, 2012
    jwjeep60

    jwjeep60 in process

    Sedalia Mo.
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    I was running a holley 1940 from a ford on my F-head for a little while, it needed a tune and was a noticeably bigger carb with a loss in mpg and low end drivability but had some more spunk in 3rd. Should bolt on to a L-head.
    it uses a piston accelerator pump like the bog boys and has a horse shoe shaped fuel bowl which is a little odd and not so good on the trail.
    grab one if you can it is a really simple carb to adapt.
    I used a 2" spacer to put it at carter height and clear the rocker cover but with an alteration to the rocker cover it could bolt directly to the head.
    don't know if that is enough because it is still higher than the rocker cover. Don't mind the extra Intake and exhaust stuff.
    [​IMG]
    [​IMG]
    [​IMG]
    I've seen a F-head in a low hood but it had the side draft
     
    Last edited: Mar 18, 2012

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