[TransAm 474]

Originally Posted by Cliff R

The later carbs have a very fine metric thread pitch so it's apprx 2 to 1 compared to 10-32 threads. The holes under the idle mixture screw are also tiny, and unless his builder opened them up some six turns out isn't alarming.

I've done a LOT of testing with intakes, spacers, etc.

I would NOT use any type of "open" spacer or adapter on a dual plane intake. If you do take the time to "slot" the spacer or adapter and install a full divider. I make them here from a piece of 1/8" thick aluminum flat bar.

It's OK to allow one side to see the other slightly, and a "notch" between the secondaries is beneficial, but if you allow very much it can and will create all sorts of running issues including "goofy" idle quality. Even worse we've ran into secondary transition and tuning issues as well.

In contrast a single plane intake pretty much requires at least a fully open 1" spacer especially with a spread bore carb on it. Having the throttle plates too deep or uneven depth in the plenum areas can cost a LOT of power and vehicle performance. In ALL cases on engine of any power level we gained considerable power on the dyno adding a 1" open spacer nicely blended into the plenum area.

Spacers on dual plane intakes not so much and I don't consider them worth the time and/funds unless you have adepuate hood clearance.

I'll also add here that when you move the carb UP, and have to move the air cleaner lid down you MUST have a minimum of 3" clearance to the top of the carb where the air cleaner gasket sit. Any less has always lost power, and even cause transition issues going quckly to full throttle that would not tune out........

Again, Thank You Cliff for the wonderful knowledge. We will do some vacuum testing and things today and report back with results. I am also still awaiting a reply from Sean Murphy to see if he will tell me all of the specifics on the carb, like upper/lower air bleed size, Downchannel size, Idle Tube Size and hole size under the mixture screws. That new Intake is suppose to ship today, so we will get that installed soon as well, and do away with that Adapter.