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By dennis22 - 4 Years Ago
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Hi everyone,
I’ve been doing a bit of reading about different intake performance and have decided to modify my B intake to a dual plane.
My questions are-
1- should I open up the 4 holes radius larger to suit the spacer I have? (See below photo with marker)
2- should I machine the top surface flat or leave the factory depression?
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By Ted - 4 Years Ago
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For normal street driving, I’ll suggest that you go with a four hole carb spacer as low end torque is improved using those rather than an open style carburetor spacer. The best bang for the buck for intake modifications comes from making the carb openings in the manifold so it has two slots rather than four holes.
Of particular interest would be this article on carb spacer testing.
http://www.eatonbalancing.com/2012/09/29/carburetor-spacer-testing/
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By Joe-JDC - 4 Years Ago
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This modification also allows the use of a phenolic spacer to keep the carburetor cooler and helps prevent fuel percolation. Joe-JDC
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By dennis22 - 4 Years Ago
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Thanks Ted and Joe.
In this instance I’ll go for the 4 bbl spacer, but hypothetically if I were to go for the dual plane modification on the manifold, would I machine the surface flat an open the holes up slightly?
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By charliemccraney - 4 Years Ago
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The manifold is already dual plane. Modifying it as Ted shows makes it work better and accommodate larger, modern carbs while maintaining dual plane functionality.
You can machine it flat. Others have used epoxy to fill in the valley in order to make it flat. The holes should be opened up to match the carburetor, at the very least.
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By dennis22 - 4 Years Ago
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I realize it already a dual plane manifold.
Ok so I just want to clarify, please correct me if I’m wrong- machine the 2 slots in the manifold but use a 4 hole spacer to retain the low end torque, correct?
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By charliemccraney - 4 Years Ago
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The spacer should be 4 hole or divided (2 ovals) in order to maintain the dual plane functionality.
Here are some examples. The one in the middle is a hybrid of the two, two ovals on bottom, 4 hole on top.
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By dennis22 - 4 Years Ago
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Nice one, thanks. I have ordered a 2inch 4hole spacer and will get the manifold machined.
Thanks Everyone for the advice, much appreciated!
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By Talkwrench - 4 Years Ago
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I assume you have a manual trans? going too big on the spacer can bugger up the linkages. From memory I just put a 4 hole 1" spacer straight on [modified for PCV] mines an Auto.
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By 1946international - 4 Years Ago
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Great info here, I think I'll try milling out the two slots. Thanks for the info.
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By 1946international - 4 Years Ago
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do you all think I would get any performance improvement doing this when running a smaller CFM 1272 or 1273 carb?
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By Ted - 4 Years Ago
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1946international (6/25/2020)
Do you all think I would get any performance improvement doing this when running a smaller CFM 1272 or 1273 carb?
Yes.
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By dennis22 - 4 Years Ago
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Just an update and to close this one out.
I got my newly modified intake manifold from the machine shop.
I also picked up my heads (now with positive type seals) and flywheel.
As always, thanks to everyone for the advice, always appreciated.
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