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Thread: Flathead vs. OHV Advantage

  1. #1
    65cruiser
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    Flathead vs. OHV Advantage

    Something I've always wondered about but never saw discussed, was why the flathead engines disappeared and the OHV engines took over? What was(is) the advantage? Was is increased HP? Surely it wasn't less moving parts as it seems any OHV engine would have more moving parts than a flathead. I've never even had a flathead unless you count a lawn mower

    I know Studebaker's first V8 was of OHV design in 51, but can't remember when Ford followed (was it 52?), then Chevy in 55. Not sure either when Caddy had their first (where they the first?) or Olds either. But, whey did the sixes lag so far behind? I don't remember OHV sixes until around 61 or so?

    I know I could Google all this but this is one of those things I woke up thinking about[|)].

    Mark Anderson
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  2. #2
    Silver Hawk Member Guido's Avatar
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    It is interesting how technology works. While Studebaker did not move to an OHV design until 1961 (and that was merely a reworked flathead), you could get one in 1935 in the new Oliver 70 tractors (which I think had 7 main bearings). Seems like other companies with a South Bend connection were more in tune to where things were headed.

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  3. #3
    Silver Hawk Member N8N's Avatar
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    two big advantages to OHV; one is a better path for the fuel/air to come in and the exhaust to go out, with the valves directly above the combustion chamber. Also a flathead has a limited compression ratio, since there must be enough room in the head for the valves to open. You don't have that limitation with an OHV. Also as the entire combustion chamber of an OHV is directly above the piston, it's slightly more efficient and there's less surface area so more heat stays where it does some good.

    nate

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  4. #4
    President Member rockinhawk's Avatar
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    Did Chevy ever have a flathead? also I remember my brothers having straight 8's. Buick was ohv, but Pontiac of the same vintage was flathead. Seems like I read where Chevy had a OHV V8 back in the teens,but no one would buy it because they said with the pistons leaning over, it would wear a hole in the block


    Neil Thornton
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  5. #5
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    Cadillac and Oldsmoble both came out with OHV V8 in 1949. Pontiac and Chevy both came out in 1955 with the OHV V8. Prior to the 1949 both Cadillac and Oldsmobile had flatheads. Cadillac a V9 and Oldsmobile a straight 8 and a straight 6. Pontiac had a straight 8 flathead and Chevy had an OHV straight 6. Ford came out in 1954 with an OHV V8. They also had an OHV straight 6.

  6. #6
    Golden Hawk Member Dick Steinkamp's Avatar
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    quote:Originally posted by rockinhawk
    Seems like I read where Chevy had a OHV V8 back in the teens
    Yep...1917...

    http://tinyurl.com/688ksc

    Here's a pic of one at a past local cruise in...





  7. #7
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    This is a Chevrolet OHV 4 cylinder at the Richmond AACA show. It has exposed rockers (no valve cover). There is a small oil can on the firewall that the driver has to stop occasionally and oil the rockers.



    Chevrolet came out with an OHV 6 in 1929, referred to as the "Stovebolt", which prompted Henry Ford to come out with the Flathead V8.

    The OHV 6 Cyl. Ford engine came out in 1952 and would outrun the Flathead V8.


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  8. #8
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    Cadillac had overhead valve V8, V12 and V16 engines starting in 1930 until the mid thirties, then reverted to flathead engines. Marmon had an overhead valve aluminum V16 in 1932. Both the Caddy ohv engines and the Marmon engine had zero lash hydraulic lifters. Buick only made one flathead engine and that was about 1910. Pontiac had a flathead V8 in 1931-32.

    Terry Godkin
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  9. #9
    Golden Hawk Member DEEPNHOCK's Avatar
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    Think manufacturing, tooling costs, and service warranty.
    If the valve train had problems with a flathead, the engine had to come out.
    If an OHV had an issue, the head could be swapped (Even in Pile O' Bones[:0]).....
    Jeff[8D]



    quote:Originally posted by 65cruiser

    Something I've always wondered about but never saw discussed, was why the flathead engines disappeared and the OHV engines took over? What was(is) the advantage? Was is increased HP? Surely it wasn't less moving parts as it seems any OHV engine would have more moving parts than a flathead. I've never even had a flathead unless you count a lawn mower
    <snip>
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  10. #10
    Golden Hawk Member
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    quote:
    Here's a pic of one at a past local cruise in...
    Now there's a small block Chevy that you can't get parts for at Wal-Mart! [)]

    Matthew Burnette
    Hazlehurst, GA



  11. #11
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    Bottom line is flatheads were cheaper to manufacture - less tooling, and machining and fewer parts. Early ones didn't even have removable cylinder heads. The first Studes with removable heads appeared in 1918. As Nate says, they were less effecient because the combustion chamber had to extend over the valves. Most were L head engines (Champion). The worst one for efficiency was the T head engine (Pierce Arrow 38, 48 and 66 horsepower). The Pierce Arrow engines had 4 valves per cylinder, in an effort to up the efficiency, so nothing new there. Chadwick was the first car to use a supercharger about 1910, the reason being the design of the induction system severly restricted the flathead engines horsepower output compared to other cars of the day.

    Terry Godkin
    Surrey. British Columbia

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