To echo Joe's comments above (if you are talking about replacing a single barrel carb with a two barrel carb and using the stock manifold and adapter):

We did a lot of testing years ago. We were not able to duplicate the performance of the original single barrel using ANY two barrel with the 2 -> 1 adapter.

We did no testing by milling out the manifold as Joe suggested, so have no comment there; but using the two barrel and adapter WITHOUT manifold modifications LOST performance (at least in ALL of our testing).

Jon.




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