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Thread: SU Mod (lifted from the net)

  1. #1
    Nova Scotia,Canada,Earth Blue's Avatar
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    Default SU Mod (lifted from the net)

    source: http://www.mgexperience.net/archive/...ovments/207908

    "On HS2s and HS4s for racing we thru-bore them, meaning no bridge what so ever, on HS2 you will actually run out of room, meaning a hole in the bottom of the carb you have to epoxy up. However for street cars this would ruin driveabilty, but with race carb nothing but wide open throttle matters. On a street car I would not worry about bridge mods, if I made any mods to a stock carb for the street I would think about beveling the slide so the square leading and trailing edge is nicely radiused towards the opening front and rear. There are a good many books on SU carbs that was mentioned above, also consider getting on chassis dyno with a air/fuel ratio meter, you might be pleasantly surprised with the gains you can make with stock carbs with the proper needles and jet adjustments."
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


  2. #2
    Nova Scotia,Canada,Earth Blue's Avatar
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    Default SU Mods (Bell Mouths and rounded piston lip)

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    note the epoxied gentle ramp leading to the bridge that still keeps the "step" for turbulence.
    Last edited by Blue; 09-04-2011 at 10:32 PM.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


  3. #3
    Nova Scotia,Canada,Earth Blue's Avatar
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    Default SU Mods (Ring Toy Bell Mouth)

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    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


  4. #4
    Nova Scotia,Canada,Earth Blue's Avatar
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    Default SU Mod (Blow Through Turbo with Twin Fuel Bowls)

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    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


  5. #5
    Nova Scotia,Canada,Earth Blue's Avatar
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    Default SU Mods (Triple SU)

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    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


  6. #6
    Nova Scotia,Canada,Earth Blue's Avatar
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    Default SU Mods (Bored Out and Ramp Bridge)

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    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


  7. #7
    Nova Scotia,Canada,Earth Blue's Avatar
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    Default

    Source: Col. Joe Hauser http://www.datsun.org/fairlady/JoeCarbs.htm


    CARBURETORS

    Under SCCA rules for G Production, the Datsun 1600 was required to run a pair of Hitachi carbs. These were very similar to British SUs. In fact the needle valve from one would fit in the other. The SCCA rules allowed substantial modifications to the carbs as long as the bore was not enlarged at the butterfly valve. So over the years we made the following modifications:-

    Rounded the front of the piston

    Removed the step at the jet

    Angled the rear of the jet to help draw fuel mixture

    Increased the diameter of the bore to a point just in front of the throttle plate (3/32")

    Thinned the throttle shaft and butterflies

    Used very light springs on top of the pistons, or no springs at all

    Tuned the intakes with velocity stacks to suit the RPM range of the engine

    Set carb float levels slightly higher than stock so no starvation at high RPM. I used brass floats. The most important and difficult part was finding the right needle end jet combination.

    My final solution was boring the stock jet larger to .095 and finding a needle that would provide a good fuel air mixture over the rev range I was using. My final solution was to customize the needle on the dyno and at the track by chucking the needle in an electric drill and dressing it down to suit. Not very scientific but it worked.

    I also matched the carburetor ports to the intake manifold ports. After some trial and error I found that by leaving the carb ports slightly smaller than the intake manifold that it was as good or better than matching and took less work. (This is the reversion factor). The intake manifold was matched to the head in the same way.

    The intake manifold was enlarged to properly match the carburetor and the head ports. The hole in the balance tube was enlarged to 9/16". This smoothed the power out put and improved the idle.



    HEADERS

    The opposite of intake is exhaust, if you get it in efficiently you must get it out efficiently. There were no good headers available for the 1600 when I started racing so I was forced to make one. Out came all the books I could find on building a good header. So I made two headers, both 4 in to one. One was made from 1" exhaust tubing and one from 1 3/4" tubing. Both were made so that I could extend or shorten the tubes to find the best length of the pipes. Tubes were made as close as possible to the same length and after much dyno and track testing we found that the 1" tubing about 29" long, dumped into a 2" pipe, gave us the best all around power output. The 2" pipe was extended to the rear of the car with a megaphone on the end. However when SCCA decreed the 104db sound requirement the megaphone had to be removed. The power loss was minimal if any.

    I loved the sound of that megaphone.


    Col. Joe Hauser
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


  8. #8
    Registered User Bonzi Lon's Avatar
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    Default

    Always great information, Blue.

    I like my Roadster's megaphone.

    Bonzi Lon
    1973 HLS30-168500
    1968 SPL311-18100
    1969 HLS30-000110 SOLD Shipped to Dubai UAE
    CZCC#11300

    Ones and Zeros

    "We drive only blue cars." Dishwalla

  9. #9
    Nova Scotia,Canada,Earth Blue's Avatar
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    Default

    Source: Col. Joe Hauser http://www.datsun.org/fairlady/JoeCarbs.htm


    CARBURETORS

    Under SCCA rules for G Production, the Datsun 1600 was required to run a pair of Hitachi carbs. These were very similar to British SUs. In fact the needle valve from one would fit in the other. The SCCA rules allowed substantial modifications to the carbs as long as the bore was not enlarged at the butterfly valve. So over the years we made the following modifications:-

    Rounded the front of the piston

    Removed the step at the jet

    Angled the rear of the jet to help draw fuel mixture

    Increased the diameter of the bore to a point just in front of the throttle plate (3/32")

    Thinned the throttle shaft and butterflies

    Used very light springs on top of the pistons, or no springs at all

    Tuned the intakes with velocity stacks to suit the RPM range of the engine

    Set carb float levels slightly higher than stock so no starvation at high RPM. I used brass floats. The most important and difficult part was finding the right needle end jet combination.

    My final solution was boring the stock jet larger to .095 and finding a needle that would provide a good fuel air mixture over the rev range I was using. My final solution was to customize the needle on the dyno and at the track by chucking the needle in an electric drill and dressing it down to suit. Not very scientific but it worked.

    I also matched the carburetor ports to the intake manifold ports. After some trial and error I found that by leaving the carb ports slightly smaller than the intake manifold that it was as good or better than matching and took less work. (This is the reversion factor). The intake manifold was matched to the head in the same way.

    The intake manifold was enlarged to properly match the carburetor and the head ports. The hole in the balance tube was enlarged to 9/16". This smoothed the power out put and improved the idle.



    HEADERS

    The opposite of intake is exhaust, if you get it in efficiently you must get it out efficiently. There were no good headers available for the 1600 when I started racing so I was forced to make one. Out came all the books I could find on building a good header. So I made two headers, both 4 in to one. One was made from 1" exhaust tubing and one from 1 3/4" tubing. Both were made so that I could extend or shorten the tubes to find the best length of the pipes. Tubes were made as close as possible to the same length and after much dyno and track testing we found that the 1" tubing about 29" long, dumped into a 2" pipe, gave us the best all around power output. The 2" pipe was extended to the rear of the car with a megaphone on the end. However when SCCA decreed the 104db sound requirement the megaphone had to be removed. The power loss was minimal if any.

    I loved the sound of that megaphone.


    Col. Joe Hauser
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


  10. #10
    Crumudgeon
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    Default

    Again, all the SU mods listed above are for track use where you're at full throttle or nothing. On a 200hp track 240Z running SUs the throttle is a light switch: brake, turn in to the corner, slap the throttle to the floor. In some cases the mods above will not allow the car to idle and you will have to keep it running by blipping the throttle.

  11. #11
    Nova Scotia,Canada,Earth Blue's Avatar
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    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


  12. #12
    Nova Scotia,Canada,Earth Blue's Avatar
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    Default

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    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


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