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Cylinder Head Testing - Wet Flow Power

Can wet flow testing show the way to improved power? It can-and Dart took the plunge big time

Dick decided that he didn't want to take just a simple step forward in an attempt to beat out the competition, but to take a quantum leap forward. With this in mind, Dick put in a call to Mondello and discussed the possibility of building a high-tech King Kong version of Joe's regular wet flow bench. A design was decided on, and a deal was struck. Six months later that bench was delivered and Tony McAfee, Dart's chief head development engineer, went to work.

For a back-to-back test like this to produce realistic and representative results, the engine used must already be at the pinnacle of development within the spec/price range it's intended to compete in. This is where Lloyd McCleary, the boss at T&L Engines came in handy. He knows engine combinations and he knows how to put that to good effect on what he concentrates on these days-affordable custom crate motors with a race-winning pedigree.

The test engine you see nearby is one of T&L's 383s just as Lloyd sells them out of the door-other than the fact we've changed the front cover to make cam changes faster. Note: Our test engine has Dart heads in the first place. Why? Because Lloyd's considerable previous dyno testing has shown that our baseline Dart heads already represented one of the best buys on the market in terms of horsepower per dollar.

And-courtesy of Maskin's foresight, Mondello's wet flow bench building, McAfee's patience toward developing the head and McCleary's engine building expertise-here are the definitive results of before and after wet flow testing.

(First let's take a quick look at the heads we're dealing with. In step #6 you can see an assembled 200cc port Pro 1 and the Platinum Pro 1 that replaces it. At first they barely look any different, but closer inspection shows otherwise.) Starting at the intake manifold face, the port entrance has been made to closer tolerances to bring about a better port match with a typical high performance intake. The other aspect that's relatively plain to see, and this applies in total to the new Platinum heads, is the smoother casting finish. But the trued up entrance to the intake port-though significant in terms of high valve lift flow when coupled to an intake manifold-are not where the real advantages of the Platinum Pro 1 heads lie. For this we have to delve much deeper.

Looking into the combustion chamber reveals most of the changes made to produce the Platinum Pro 1 head. First take a look at the original Pro 1 head then check out the differences depicted by the arrows in the adjacent photo. Going through these in order we first have the introduction of a long guide vane in front of the guide boss. This serves a number of purposes. First it provides better streamlining of the guide boss, which proves beneficial both in terms of a small increase in high-lift flow, plus a small increase in velocity throughout the lift range if the guide boss reduced port volume.

In addition to this, the pre-guide boss vane can be used to change the path of wet fuel flow within the port and the swirl characteristics. The trailing guide vane (arrow #2) also serves in much the same way. The area indicated by arrow #3 is scalloped out slightly deeper than is seen on the original Pro 1 head. This has the effect of turning the charge more as it enters the cylinder, thus generating a better swirl action. The small area indicated by arrow #4 looks seemingly unchanged, but as little as 0.020 of metal added to this point can benefit the swirl greatly, especially in the 0.400-inch lift range on up. It can also eliminate the intake valve airflow tip-over so often seen at about the 0.600-inch lift point on 23-degree SB Chevy heads. The area indicated by arrow #5 has been scalloped away more than the original Pro 1 head, and the bump to the right evident on the original has been eliminated. In addition to this, the plug has been repositioned.

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