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Join Date: Dec 2002
Location: Boulder Colorado
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opening up manifolds for weber 46s

I have some weber 40 manifolds (corroded barrels)) that I would like to use with my Weber 46s. Is there a typical strategy? Top of the manifolds need to match bottom of the carbs, and taper to match the opening in the heads? I am going to assume that I can use a gasket as a template for both sides of the manifold. Is the typical manifold for Weber 46s a 42mm-38mm sizing? Am I crazy to think that I could "mill" the tops and bottoms of the manifolds to the correct size and then use my die grinder to massage/blend the taper in the throats? How do the "big boys" perform this?

TIA Speedo
Old 01-29-2019, 07:00 AM
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Quote:
Originally Posted by speedo View Post
I have some weber 40 manifolds (corroded barrels)) that I would like to use with my Weber 46s. Is there a typical strategy? Top of the manifolds need to match bottom of the carbs, and taper to match the opening in the heads? I am going to assume that I can use a gasket as a template for both sides of the manifold. Is the typical manifold for Weber 46s a 42mm-38mm sizing? Am I crazy to think that I could "mill" the tops and bottoms of the manifolds to the correct size and then use my die grinder to massage/blend the taper in the throats? How do the "big boys" perform this?

TIA Speedo
Buying new PMO manifolds would be easier, but sure, it's what I did to match port my manifolds to my big port SC heads.
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Old 01-29-2019, 04:42 PM
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machining manifolds

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Originally Posted by Mark Henry View Post
Buying new PMO manifolds would be easier, but sure, it's what I did to match port my manifolds to my big port SC heads.
Thanks Mark, just not sure what you meant...you bought PMO manifolds to match your Webers to your big port SC heads, or you machined your manifolds to match your Webers to your big port SC heads?

I like the PMO manifolds wihout question and have them on several engines. And they come in different flavors (sizes of exits).
But to me, the earlier original manifolds look more "right" (a tall set of R manifold would really look "right"). And these 40mm manifolds need to be cleaned up anyway as they are a bit crusty. The way the barrels look currently...there would be more than the required amount of flow "turbulence"...just say'in.

Still am curious about the machining procedure...machine both ends on a mill, and then die grind to taper?
Old 01-29-2019, 05:38 PM
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I ported original manifolds, I also made machined aluminum and phenolic spacers.
I did most of the manifolds by hand with burrs and flap wheels on a die grinder.

I used an aluminum spacer because the CIS injector notch on the SC head port can cause sealing issues with the original manifolds The original manifolds head flange doesn't have a whole lot of meat on them.
The phenolic spacers to reduce carb heat.
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Old 01-29-2019, 06:35 PM
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Mark; how thick did you make the aluminum spacers ? I'd prefer to buy them, ID 34-38 mm if possible but so far no luck.
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Old 01-31-2019, 02:12 AM
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Originally Posted by trond View Post
Mark; how thick did you make the aluminum spacers ? I'd prefer to buy them, ID 34-38 mm if possible but so far no luck.
Honestly I can't remember, the motor is sitting right here and the spacers sits flush with the shroud, maybe 1/8" or 3mm.
I made them and the 1/4" phenolic spacers myself with a jig on the lathe.

In the pic below shows what I did, but the order is wrong, the aluminum spacer should be on the bottom.


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Last edited by Mark Henry; 01-31-2019 at 10:00 AM..
Old 01-31-2019, 09:53 AM
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