Is this necessary on the Offenhauser as a result of #'s 2& 5 running a bit lean. I thought it was cylinders 1 and 6 that were often rich...

See picture #5,

https://www.ebay.com/itm/317847802916?_ ... R4TzstSLZw

Absolutely not needed. Probably won't really hurt anything either. Yes, 1 and 6 might run slightly richer, but it is very slight. Unless your carb is really messed up or trying to run right on the edge of lean or detonation, the cylinder-cylinder distribution is very good on all common Slant 6 manifolds.

That said, with a 2bbl mounted with barrels side-side like that, I usually run about 2-3 (holley) jet sizes bigger on the inner barrel and can see a small difference in the plugs if I bother to check.

Lou

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Home of Slant6-powered fun machines since 1988

The old Mopar Performance racing manual used to recommend a fuel dam like that behid the secondary throttle bores on a normally oriented four barrel intake to combat the tendency of the middle cylinders to run richer than the outer.

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Casually looking for a Clifford hyperpak intake for cheap.