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The Skinner Union
Carburator....    De-mystified
Tuning vs
Adjusting SUs
Twin HS4's vs
single ZS CD150
The Fuel
Flow Path

   The Comparison.
      Running a single Stromberg 150  vs. twin SU HS4's

      This site is progressively being updated as the on-going tests are completed. The information being documented here will compare tuning and performance issues for running a twin SU's vs the stock single ZS150 carburetor.

   The test platform for this round is a 1975 Triumph Spitfire. Our test bed is Bone stock.




The Competitors  

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Zienith Stromberg 150CD

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DCOE 40 2

    The single DCOE 45 is mounted on a Pierce manifold via a 'soft-mount' gasket system. This isolates small dynamic vibrations that can effect emulsion tube and various chamber internal chamber 'fuel level'

The pair of DCOE 40's being used are mounted on twin 'parallel port' Cannon manifolds, via a soft-mount system. At this stage a throttle linkage still needs to be decided on. The manifolds have already been modified with crossover pipes

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    Well before I get into all the technical stuff, here's a few photos of the two setups and the test platform.

       This is just a visual comparison of the two carb schemes. The 45 has been on the car for the last 250 miles. The recent winter weather has slowed me down just a bit. But testing will get going again very soon.

dcoe45_x2_40s.jpg (35067 bytes)  

dcoe45_40s_top.jpg (18287 bytes)     Just a couple of comparison shots. I'm in the mild of figuring out linkages, spacing, filter size selection and piping routings.

    One thing I like already. The dual DCOE 40 setup from manifold to filter edge, is roughly 1.5" shorter. That means I can run longer am pipes than what I can use with the DCOE 45. The 45 as installed, is running 26mm ram pipes inside a 2" deep air filter. This setup give me only 1/4"-1/2" of clearance with the bonnet when opening and closing it.

    With the shorter manifold length, I'll be able to go up to say, a 3" deep filter. This will allow me to run up to 39mm long ram pipes.

    The present DCOE 45 air filter setup is a K&N free flow unit. At present, I'm looking at developing a single box K&N filter system that either: 1) wraps around both carbs (almost modeling the single carb design, or the logo plate MGB, Sprite and Midget units)  or 2) A Plenum at the carbs, with a tube for a cold air feed from a Single large K&N filter mounted in front of the radiator.
...we'll have to see how it goes...

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40s_crossover tubes.jpg (14382 bytes)    Cross over pipes

     This is the crossover porting built from copper piping and brass compression fittings. The entries into the manifold throats were ground flush to match the profiles of the inner walls. The 'T' between manifolds (with the large outside thread) has not been tightened yet. This is the valve cover connection, and will be tightened after the carbs are mounted to the head. This allows for carb to carb, center-to-center variations.
     You may ask why would you port the individual runners together? I believe for road use, a small amount of bleed over helps steady state cruising. Plus, to maintain proper crankcase pressure (vacuum) you still need crankcase to intake vacuum tap.       
      The last little section of piping (that connects directly to the valve cover), is designed to be 'crimped' to limit pressure pulses. Hence, the four throats would share a more common vacuum pulse interaction in comparison to that of any flowing into/out of, the crankcase. A standard in line PCV valve will also be installed and tested here, as well as simply testing a 'crimped' connection to regulate the crankcase pressure.top.gif (1043 bytes)


     Initial Jetting Information

These tables list my initial Jettings used for this first round of testing. Why I'm starting with these settings is whole 'nother story of it's own. I hope to add full road dyno info concerning the settings and testing results of whatever jetting configuration is found to work the best.

DCOE 45 13
Choke 34
Aux. Venturi 3.5
Main Jet 150
Emulsion Tube F2
Air Jet 175
Pump 45
Idler Jet 55F8
Ex.Valve 50

45 jetting

DCOE 45 152
Choke 34
Aux. Venturi 4.5
Main Jet 145
Emulsion Tube F16
Air Jet 155
Pump 45
Idler Jet 55F8
Ex.Valve 40

45 jetting

DCOE 40 18
Choke 30
Aux. Venturi 4.5
Main Jet 115
Emulsion Tube F16
Air Jet 170
Pump 50
Idler Jet 45F9
Ex.Valve 50

40 jetting

DCOE 40 2
Choke 30
Aux. Venturi 4.5
Main Jet 135
Emulsion Tube F15
Air Jet 170
Pump 45
Idler Jet 60F5
Ex.Valve 35

40 jetting

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last edited 2/1/2003

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