6/carbs: ? about tall 2ndary venturi's, rich, I miss you. Options

[brant]

carbs: ? about tall 2ndary venturi's
Hi all... thanks for the help in advance.

I want to try a set of the tall 2ndary's on my IDS-3C carbs.
I'm running the stock ones and want to try the tall ones, that I've heard called "906-style"

its a race car and withoug re-hashing all of my jetting and dyno history, my questions are:

1) pierce manifold says they have 2 different types in stock a 3.5 size and a 4.5 size. I believe this measurement is in reference to bore and not height. Pierce said that both sizes are the "tall" type. Which do I want? Motor is a 1967 2.0/S motor at altitude.
(the pierce catalogue references that the IDS carbs came with 4.5 short, but I'd like confirmation before I order)

2) Does anyone know if these tall secondaries interchange on the IDA carb versus the IDS carb. I would assume so, but I once bought some F33 emulsion tubes from Pierce that do fit the IDA, and found that they would not fit the IDS. I didn't know there was that much difference between the two carbs, which surprised me. But again, before I order do people know if the 906-type tall 2ndaries will fit an IDS-3C body?

again, thanks in advance everyone!
brant

[Jake Raby]

All my testing would not apply to the six... It has different head characteristics that really impact results.

On a /4 no matter displacement I have found shorter stacks(just enough to control reversion) are mucho better for top end power and efficiency, while tall stacks are much better for low end grunt... BUT even the exhaust system will impact this-

I have seen a 18HP variance just from swapping stacks on an 8,000 RPM capable engine.

But I'll stress that my theory has never been employed on the six-