Tech info: Holley fast idle cam cages

[VintageMusclecar]

It seems there's quite a bit of confusion on the subject of what fast idle cam cages are correct on what carbs, so here's a quick run-down of the 4 most common types.

First, you have the style that was used on 1966 through 1969 carbs, and on the 1970 smallblock carbs. This is also the style that is used on all current Holley GM service replacement carbs. While it isn't "technically" correct for all GM applications (namely the `70 big blocks, which I'll get to in a moment), it can be made to function acceptably.

Next, you have the style that was used on the 1970 big block carbs installed on the lowrise intake. This is very similar in design to the `66-`69 style, but it features a slight dog-leg in the arm where the choke rod (from the choke stove on the intake) attaches. Unfortunately, these cages are extremely difficult to locate, and I'm told that Holley has no plans to reproduce them anytime soon.

Nest, you have the style that was used on 1971 and 1972 GM Holley carbs. This unit is not interchangeable with any other units, and is required on the `71-`72 carbs.

Lastly there is the Chrysler style cage, which is easy to mistake for the `70 big block GM style at a glance unless you're paying attention.

In the pics below;

"A" is the common `66-`69 style (and `70 smallblock) which is also the one used on the current release Holley service carbs

"B" is the correct "stepped" `70 big block only cam cage.

"C" is the `71-`72 style GM cage which is also stepped similarly to the `70 unit, but not interchangeable with it

"D" is a Chrysler stepped style cam cage and is not interchangeable with any of the GM style cages.



Hope this helps clear this up. If you have any questions, feel free to ask.

Eric