P-4B 4 PMD

I need to find the stock intake manifold height on a '76 Trans Am 455 motor and the height of a Edelbrock P-4B intake. (Edelbrock doesn't archive specs on this old intake.)

Ray Woods
Dallas, Texas

Rocky Rotella responds: The P-4B may be the most challenging Edelbrock intake manifold to understand because so many variations were made over the years. The short answer to your question is that in my experience, the P-4B, regardless of variation, places the carburetor in the same relative position as the stock intake manifold from a front/rear bias perspective. The carburetor-flange height is, however, slightly lower at the rear when compared to stock, by about a half-inch or more.

To restore the factory carburetor height needed to position your Trans Am's Shaker in its original location, the best solution may be to fashion a wedge-shaped spacer to raise the rear portion. You'll find the exact dimensions will have to be tailored to your particular application. You can construct a spacer of soft wood, which can be permanently installed, or have a local machine shop transfer its dimensions to a common resin spacer readily available on the aftermarket. You may have to elongate the mounting-bolt holes to keep the fasteners from binding.

Let me take a moment to discuss the basics of the various P-4B manifolds that Edelbrock made over the years. You may find that the particular P-4B you have might not actually perform any better than the correct factory cast-iron intake manifold for your application, negating the effort required to install it and create a custom carburetor spacer.

The P-4B first appeared in Edelbrock's 1967 catalog as a high-performance replacement for Pontiac V-8 applications from '65 forward. The following year, an EP-4B for '64-and-earlier Pontiac V-8s was made available. It was virtually identical to the P-4B, but its exhaust crossover and cylinder-head-flange bolt-pattern were redesigned to accommodate earlier equipment.

The original P-4B contained a carburetor flange with two distinct bolt patterns—both accept Holley four-barrels only. It featured a large plenum with wider, more smoothly contoured runners. The fastener holes for the thermostat neck were cocked slightly to accommodate the width of the leading runners. The Edelbrock script logo and P-4B identifier were also located next to the thermostat housing.

While the original design performs better than a factory cast-iron intake on the flow bench and in high-horsepower applications on the dyno/race track, its larger runners can make it a bit more challenging to fit and tighten all of the retaining bolts. It can also make installing an HEI distributor tough as the rear runners can occupy the space required for the HEI's wide cap and retaining fastener lugs. The manifold also only accepts the single-bolt throttle- cable bracket used through '71 and limited choke-coil options.

In the early '70s, Edelbrock released a modified version of the original P-4B, specifically designed to accommodate the spread-bore Quadrajet carburetor. Named P4B-QJ, its plenum size and runner dimensions were identical the original P-4B, but its carburetor flange was shaped and drilled/tapped specifically for the Quadrajet only. It also accepted a stock Pontiac '71-'72 divorced-type choke coil, '72-'74 throttle bracket, and contains smaller, square-shaped exhaust-crossover holes matching the cylinder heads from '72 forward. It proved an excellent performer, but shared the same installation hurdles as the original.

At some point during the '70s Edelbrock revised the P-4B. This later design appears, fits, and functions very much like the modern Performer we know today, including its dual-bolt pattern on the carburetor flange for square- and spread-bore units. The divorced style choke eventually gave way to a flange that accepts the heat-tube style introduced for '73. Some others with various characteristics likely exist. Ironically, the P-4B was last cataloged by Edelbrock in 1982, and it appears to have been mildly redesigned further and cataloged in 1983 as the Performer.

My own testing shows that the Performer fits and functions similarly to a stock iron intake; based on its direct lineage, I'd expect the later P-4B to mimic that. The advantage that the later P-4B design (and modern Performer) offers over a stocker is a weight savings of 15 pounds or so, but any installation issues you might encounter trying to retain your Trans Am's original equipment can negate that, especially if you won't see any performance improvement. Now if your engine produces 450 hp or more and you have an original P-4B or P4B-QJ, you'll likely see some high-rpm performance advantages in addition to the weight savings, and that may definitely be worth your effort!

B-Body Breather

My '68 Catalina wagon has a 400 and I want to put headers on it. I can't find ones specifically for the Catalina. What will work?

Derik Luedt
Via Internet

Rocky Rotella responds: Derik, while I have no experience fitting tubular headers on a B-body like yours, I'm aware of a few options, but only if your 400 is equipped with D-port cylinder heads.

Doug's Headers (www.pertronix.com) has a set that reportedly fits late-'60s Catalinas quite well. Doug's D521 (with ceramic coating) is a four-tube design that features 1.75-inch-diameter primary tubes and 3-inch collectors; it retails for about $850 per set. The same header is also available uncoated for about $675 per set. If your Catalina is equipped with a column-mounted shifter, the tubes can interfere with the back-drive linkage, so be prepared to do some fabrication or modification during the install.

If you're simply looking for a performance boost and prefer an option that installs into your B-body chassis with little to no modification, consider a set of long-branch manifolds. Ram Air Restoration Enterprises (RARE) offers a high-quality reproduction (PN LB-1) that features 2.5-inch collectors intended to improve performance over the original design. They retail for less than $500 per pair (coating is $200 extra) and can be purchased directly from RARE, along with the appropriate oil-filter-housing adapter. Check out www.ramairrestoration.com for more information.

The original P-4B contained a carburetor flange with two distinct bolt patterns—both accept Holley four-barrels only. It featured a large plenum with wider, more smoothly contoured runners.

Email questions to christopher.phillip@sorc.com