Holley 660 CS

[StanJ]

Originally Posted by 427 S/O

Looking for a couple of decent, original, no damage, rebuildable Holley 660 Center Squirters.

Thanks

Of course, there are a few very straightforward and valid reasons for why someone might want a pair of center-squirters, but those reasons are most definitely “packaging”-related rather than performance-related. These carburetors were designed specifically for drag racing competition in vehicles utilizing manual transmissions, and several aspects of their design seriously compromise their ability to perform well in other applications.

As originally manufactured by Holley, the #4224 660-cfm center-squirter carbs (and their lesser known #4543 850-cfm brethren) used the short “side-hung float” fuel bowls and a fixed orifice metering “plate” underneath the secondary bowl rather than a metering block with replaceable jets. These differences made the overall length of the carburetor somewhat shorter than most of Holley’s other competition four-barrel carbs, allowing a pair of them to be mounted conventionally (rather than having to be turned sideways with all the throttle linkage headaches that can incur) on most 2X4 manifolds of the day. With their intended application, the need for mechanical opening of the secondary venturis on these carbs was a given…but that is where the problems start. Without a true metering block on the secondary side, there was no practical way for Holley to utilize two accelerator pumps on each carburetor, and precise control over the secondary curb idle and transition fuel circuits (which would have helped reduce the need for a second accelerator pump) was impossible.

Holley’s solution to the problem was to use a single, large “50cc” accelerator pump mounted on the primary float bowl to provide fuel to all four venturis simultaneously through a common “center” squirter nozzle. Now, here’s the rub…to avoid dumping that fuel in on top of closed secondary throttle blades and having it drip into the manifold during part-throttle operation, these carbs were designed with near-simultaneous “1 to 1” secondary throttle actuation which often made the vehicles they were used on a handful to stage at the race track…much less drive in traffic on the street. Over the years, racers and carburetor tuners have tried various ways of incorporating progressive secondary throttle actuation with these carbs…and some of those band-aids (such as multi-rate discharge nozzles) do help. Ultimately though, you end up picking your poison – you either deal with a hair-trigger throttle, snotty part-throttle operation…or some combination of both.

The second part of my questioning “why” centers around the fact that there is absolutely nothing “magical” about the 660’s whatsoever; the venturi shape/size/geometry of these carbs is identical to that of the less expensive (and far more flexible, tuning-wise) #4777 650-cfm double pumper. In fact, both the #4224 and #4777 are cast with the same venturi shape as the lowly #1850 vacuum-secondary 600-cfm 4brl. They only “become” larger cfm carbs when fitted with their 1-11/16th throttle-bore baseplates, which Holley does after a simple (and often crudely machined) 45-degree chamfer to the bottom of the venturis. All three of the carbs mentioned use exactly the same booster (main circuit discharge nozzle) design.

If you’re re-creating an engine package that demands “historical” accuracy, or if you’re bent on using a pair of these carbs mounted conventionally on a dual-quad manifold that you don’t want to modify (after all, gaining the necessary additional .700” worth of room is precisely why – on the 8th day -- God created the T.I.G. ), then yeah…use the 660’s. But if none of the above apply, start with something else; you’ll be a lot happier with how it runs in the end.