This wasn't the engine we...
This wasn't the engine we dyno tested but one that was in Wilson's shop. We used a 0.035+ 455 with 6X cylinder heads and a solid roller cam for our test.
At first glance, it's easy to take a Pontiac intake manifold for granted. It appears to be nothing more than an intermediate component that's used to connect the carburetor to the cylinder heads. But under further examination, it's discovered that it plays a dominant role in determining the character of a Pontiac engine and how much power it produces. Not until the General Motors designs that incorporated variable runner geometry emerged in the '90s did a manifold contain any moving parts. It works through a collaboration of theories, internal and external to the engine. If calculated properly, the manifold helps produce power, while an improper design would hinder output.
Even though this primer includes an extensive review of Pontiac intake manifold basics, it's not just about that. HPP was recently introduced to a new carburetor spacer produced by Wilson Manifolds. Keith Wilson, the proprietor and brain trust behind the spacer, has made a career out of working with engine airflow.
At 17 years old, he was employed at a Florida company called Air Speed Engineering. There, he spent 10 years porting cylinder heads and intake manifolds. In 1985 he branched out on his own and formed Wilson Manifolds. Very quickly, he seized the opportunity to not only rework cast-aluminum intake manifolds, but also to explore his theories on cylinder filling with designs constructed of sheetmetal. This became the impetus for a new spacer theory that features a tapered bore and the promise of a large power gain with almost every intake manifold. HPP was curious to see how the Wilson tapered spacer would work on a traditional street/strip Pontiac engine.
Wilson produces a full line...
Wilson produces a full line of tapered spacers for both Holley 4150 and 4500 bolt patterns. A part number for the Q-jet is also offered.
Our original exposure to this spacer was during the dyno testing of a street/strip 455 built by Jim Taylor Engine Service. The buildup of this engine was featured in the April and May '09 issues. During the dyno testing session, HPP tried both a 1- and 2-inch Wilson tapered spacer on the almost 500hp engine. The spacers worked, but in that application the 2-inch design didn't produce the results of the shorter version. Thus, we were curious about the theory behind the Wilson design and wanted to attach a science as to why the 1-inch difference in height impacted our subject engine.
Any carburetor spacer works in conjunction with the intake manifold, so HPP felt it was important to begin with an abbreviated review of intake theory.
The Intake Manifold
Any reference in this primer to gasoline will be identified as fuel. Air in scientific terms is considered a gas. By definition, a gas is any substance that is in a rarefied state.
When the height of the spacer...
When the height of the spacer is changed, the taper needs to be engineered for that dimension to be effective.
The laws of physics have proven that a gas doesn't like to make turns and will experience flow losses from friction when asked to travel in a nonlinear path. For this reason, the ideal intake path would have no bends and be a straight shot to the port of the head and intake valve. This isn't possible on a production-style Pontiac engine due to hood interference and the packaging of accessories such as the alternator, air conditioner, and power-steering pump.
Terms commonly used to describe intake manifolds have been misunderstood and need to be established.
Wet flow:
Describing an intake that has both fuel and air coursing through the runners. The best example being a traditional carburetor application.
Dry flow:
The runner carries only air with the fuel administered near the union of the cylinder head and manifold. Port fuel-injection systems are considered to be dry flow even though the injector is fitted to the end of the runner. Throttle-body injection systems are wet flow since the fuel is mixed with the air prior to entry into the manifold.
Plenum:
The McGraw-Hill Dictionary of Engineering describes it as, "A condition in which air pressure in an enclosed space is greater than that of the outside atmosphere."