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

[Thorshammer]

Tim is right.

Late injected fuel injection has the least possible reversion, and this is one of the reasons they are so tunable. And with that said, the timing event of the injection is preset and does not change with RPM and that can still produce some reversion, but with modern engines we don't see it, because it is completely contained within the inlet tract/manifold. However, you will still see reversion with a velocity stack manifold and injection at certain RPMS, although it will be reduced. And the reason that is: many FI systems do not change the degree at which the injector fires throughout the range, although some do. So (especially with race systems) you get a slight trade off when you decide on a degree of crank rotation to fire the injectors, when this timing happens it will not be perfect for all rpms, many FI tuners actually tune to inject the fuel very late in the cycle so that as lower rpms there is little or no reversion, this is common on 911 air cooled engines to also cool the inlet valves. But at very high rpms, you will normally see the engine lean out when this is set to late. In many engines FI is still a trade off of fuel distribution and powerr delivery, but then again, is it a race motor, or a street motor. If it is a street motor, you can do this because the time at high rpms is not as much as in a race motor. Then again, some FI systems will change the fuel injection timing based on rpm, and it is not fixed. which solves the problem except on valve overlap and off the gas, this changes everything. (IMG:http://www.914world.com/bbs2/html/emoticons/aktion035.gif)
If I had my druthers, I'd have injection.
Erik Madsen