A Manifold for Mr. William Tyler Jenkins… and others

We’re shared in previous MaxChevy columns that it was common practice during the '70s and '80s for specialty parts manufacturers (particularly those building race parts) to tailor products to the specific needs of notable racers.  Several benefits spun out of such efforts.  One was an opportunity to combine engineering and racer skills so that both factions learned from the experience and relationship.  It was not uncommon that new products for street use might contain features iterated from the race application.  It happened frequently at Edelbrock. 

Another potential benefit, from an advertising and marketing slant, was that the parts manufacturer could tout working with prominent racers.  It helped build credibility for the brand once such working relationships were made public.  But there were times when it wasn’t possible to divulge what was going on.  So before we spin off to talk about Mr. Jenkins, here’s one little project that’s OK to share, now that a number of years have passed.

It was a time when Chevrolet was actively working with a particular cylinder head company with whom Edelbrock had a fairly close relationship. They were also quite close with a couple of leading NASCA teams, to the extent that one of GM’s top cylinder head staffers was assigned to combine talents with Edelbrock and the cylinder head shop… for the purpose of benefitting one of the NASCAR teams, primarily to help make them more competitive with regard to engine performance.

Recognizing that an intake manifold, in terms of functionality, is an extension of cylinder head intake ports, integrating the two would be a logical objective.  It was also a time when both Chevrolet and certain head shops were discovering the benefits from raising intake ports in the small-block heads. 

So here’s what we did.  Using a Victor Jr. manifold as the guinea pig, we had the foundry provide us some solid port cores.  Starting at the manifold flange portion of each runner, we shaved off 3/8-inch of core material, blending this back to the floor of the plenum so that the manifold runner floors were effectively raised by the amount of material we removed from the cores.  Once the manifold was cast, we built up the runner roofs with aluminum welds, raising the roofs by an amount comparable to the height we’d raised the runner floors.  Following some judicious grinding, especially on the outside of the runners, and blending the material so that it wasn’t possible to detect the added material, the manifold was sand-blasted and finish-machined. 

While we had been prepping the intake, the cylinder head shop and Chevrolet engineer had been raising the intake ports in the heads to be used by the same amount as the manifold, re-working the short-side radius of each port to accommodate the raised runners.  Once all the hand work was completed, altered surfaces sand-blasted and machining done, from outside heads and manifold it was virtually impossible to identify the changes.  The net effect?  Roughly 30 horsepower over the unmodified parts, and the best of my knowledge, NASCAR never discovered the modifications, even after the engine was once in a winning car.

OK, that was pretty extreme.  But there was much more common and less extensive “tailoring” occurring with other racers’ engines.  And this brings us back to Mr. Jenkins.  Pro Stock was in its infancy and Bill was running a big-block.  Those knowledgable in the history of these engines will remember the intake ports were Siamese, resulting in what was then commonly referred to as one good port and one bad port based on differences in air flow, at least as cast if not after modification.   In the day, designing intake manifolds that would not create any restriction to cylinder head flow was the general goal.  But if you considered that four of a big-block’s inlet ports would flow more than the remaining four, would logic not tell you the manifold should be sized accordingly?  To that point, nobody had done that, at least to our knowledge at the time.