1956 4bbl carb 2nd-ary air valve

[WCraigH]

In the latest issue of "Hot Rod" magazine (April 2003) there's an article about the "new" Edelbrock AVS carb. As you may know, the Edelbrock "Performer" series of carbs is a repackaging of the venerable Carter AFB carb series, with a few improvements.

This is a good thing so that there's something besides a Holley carb to choose from if you're going aftermarket. I've seen a couple of Packard V-8s with Edelbrock/Carter carbs retrofitted, so it's a viable choice if the original Rochester 4GC or Carter WCFB are worn out.

Anyway, the article makes a big point about the AVS (Air Valve Secondary) enhancement compared to the standard AFB. The AVS design is very similar to the Rochester Quadrajet secondary air valve except the AVS uses high speed venturis ("booster clusters", for better atomization, says the article) rather than brass dump tubes. It also has an externally adjustable spring tension to control the rate of air valve opening (also like the QJet).

Interestingly, the 1956 Packard 4bbl carbs also had secondary air valves, although the service manual calls it an "auxiliary throttle valve assembly." The Rochester 4GC for 1956 and the Carter WCFB both had this feature. The purpose of the 2nd-ary air valves were (and still are) to prevent full throttle "bog" at launch given a heavy car (>4000lbs), street gearing (<3.54:1) and a tight torque converter (<1700rpm).

The article claims that the AVS was originally introduced on certain 1966 Chevys and most 1968+ Chryslers. It appears that the article's author was unaware of these earlier AVS-type carbs.

Does anyone know if the "AVS" design was used earlier than the 1956 Packard (I wouldn't be surprised)? Also, how adjustable is the "AVS" in these carbs and how well does it work compared to the non-AVS in the 1955 equivalent models?

One final comment: I'm continually amazed when reading "Hot Rod" and other mags of that ilk on how little things have changed since the 1950-60s EXCEPT for computerized-tuning of FI on late models!

[joe kastellic]

Hi, Craig, i was going through the forum, and this thread caught my eye , i ran a 68 super bee 440-375hp++++ and used the carter avs carb (stock) i remember there is adjustment for the air valve, i did get better throtle response by i thimk by loseing the spring. this was a tune tip by mopar at the time. this was 1968! i might have this info. some place joe

[WCraigH]

In my original post, I mentioned the Rochestor Quadrajet. During the late 1960s and 1970s, the QJet was spoken of derisively as "Quadra-Junk". Most were replaced with spread-bore Holleys (a piece of junk) or the Carter ThermoQuad (a really good carb).

Today (OK, the last decade), high perf enthusiasts have come to realize that the QJet is truly an outstanding carb; one just has to be somewhat selective on which model to use as some are overcome with techno-fixes to meet ever changing and more stringent emissions standards during the 1970s and early 1980s.

The QJet has two means to adjust the 2nd-ary air valve. One is a spring and one is a "vacuum break". They act sort of like the spring and shock combo on a suspension, i.e., the combination is critical.

A casual backyard hot rodder could easily adjust the tension (if they owned a small allen wrench) and usually the "best" adjustment was to loosen the spring somewhat, depending upon what other mods had been done to the car.

Modifying the "release rate" of the vacuum break was somewhat more difficult since it required enlarging the bleed hole (to speed up air valve opening) for quicker response. It was also possible to slow down the air valve opening by making the bleed hole smaller, but for hot rod purposes, this usually wasn't required.

A third adjustment could be made to the ultimate angle of the air valve at WOT, but this was only required in the case of early Firebirds which by GM mandate had to have 10HP less than exactly the same engine in GTOs. This was a LB/HP limit imposed by GM corporate. Pontiac reduced the HP by limiting either the air valve opening and/or the 2nd-ary throttle valve opening angles to less than optimum. Hot rodders also quickly figured out this mod.

Like I originally posted, technology in carbs has been essentially stagnant for many decades. But because of nostalgia (muscle cars), NASCAR and NHRA rules (refusing to evolve to EFI), carbs and their mods are alive and well. <img src="http://www.aaca.org/ubbthreads/images/graemlins/grin.gif" alt="" />

[joe kastellic]

I CANNOT AGREE WITH YOU MORE ABOUT QUARDREAJET CARB, I have used a modified Quaddrajet by the CARB. SHOP in Cailf. when i owned a W-30 ODLS. the vaccum signals that are produced by the Quadrajet work extremely well for the ODLS motor case closed!!! what do think about useing a modified Quaddrajet on a PACKARD V8 ??? maybe you should start a new theard on this subject thanks again for your great imput on this subject. joe

[WCraigH]

I would love to use a QJet on my Panther engine, but the problem is intake manifold. The 2nd-ary throttle bores are so large on a QJet that they extend out a good 1/2" beyond the cast material on the Packard 4bbl intake. Also, the primaries don't line up either. This mismatch wouldn't be solved with an adapter plate either (you wouldn't want to use one anyway).

From info on other threads, it seems like the 413-440 Chrysler intake [color:"red"] MIGHT fit the Packard V-8, at least with a simple pair of adapter plates. If so, then the Edelbrock #2191 aluminum intake would be a candidate for QJet on a Packard V-8. See this link for a picture of same:

Edelbrock 2191 Intake Manifold

Thanks for the idea! If I can locate somebody with a 413-440 intake laying around, I'll mock it up and see what's what.

Re: The Carb Shop: I've never used them myself (I do my own carb work), but I've heard lots of good things about them.