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

David Vizard Jun 20, 2007 0 Comment(s)
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Here's a finished example of a T&L-built Dart Platinum-headed crate motor. Less headers and those fancy March front-end accessories, but otherwise complete with carb and ignition, this 383 stroker made just over 500 hp and 500 lb-ft for a cost, including a dyno sheet, of less than $4,500.

Wet flow testing has moved in and out of the realms of mainstream power topics many times during the last 40 years. Like many aspects of race engine development that are a step aside of normally debated subjects, wet flow testing has both staunch supporters and detractors. That leaves a huge majority middle group who are just waiting to see the results support the rhetoric. If you're one of many waiting for the touted advantages of wet flow testing to actually show test results that equate to an undisputed power advantage, your patience has just been rewarded. But before we look at any test results, we need to look more deeply into what wet flow testing is, how it needs to be done to actually achieve positive results and, lastly, what qualifies me to write about the subject.

Back in the mid-'80s the late Ken Sperling, then boss of AFR, got on a roll with wet flow testing his then-new aluminum Chevy heads and the NASCAR heads he was doing. And the next thing you know, a mutual friend, Roger "Dr. Air" Helgesen turns up at my California shop with an armful of gear to do wet flow testing and, as usual, is hot to trot. This, along with some of Smokey Yunick's preaching, was, so to speak, my baptism into the world of how fuel/air mixes react in the induction tract of a single four-barrel carbureted high performance V-8 engine. Since the Ken Sperling wet flow era of the mid- and late-'80s, wet flow seemed dormant on the editorial front until about 2002. This is when Joe Mondello's innovative wet flow bench hit the headlines.

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Joe Mondello sets up his regular wet flow bench system at his cylinder head school in Tennessee. Basically the "wet part" seen on the left of this bench attaches to any regular flow bench. This makes it a relatively inexpensive upgrade for any existing bench.

Wet flow testing is far from complicated, but, like most things, if not done right it can be mostly meaningless. First and most obvious is that without some really good fire/explosion precautions, you cannot wet flow with gasoline. This means that whatever liquid replaces the fuel must have some or all of its primary characteristics modified so that in all relevant respects it reacts like gasoline other than the fact it won't burn. If water or alcohol/water mixes are used, the surface tension of the mixture needs to be similar to gasoline.

Also, the air-to-liquid ratio is important. The most meaningful results are when the air-to-test-liquid ratio is about 15 percent less (leaner) by volume than the air/fuel ratio the engine normally runs. The entire system being tested needs to be run at a temperature a little hotter than the mixture temperature normally seen in the intake tract of a high performance engine (about 60 degrees Fahrenheit). Running the test liquid at 90 or even 100 degrees F seems to offset the fact that the intake valve will be a lot cooler in the test bench mode than in a running engine.

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Dart's wet flow bench is, by any standards, a large piece of equipment. What we see here is the end where all the measurements take place. The screen reads out mixture ratio, as well as a host of other factors.

Components such as heads, intakes, and carbs can be analyzed separately. However, the final analysis is best done as a system, because there is a domino effect by each component as the charge progresses through the system. Any time a carb is involved, the booster action of the model needs to reasonably replicate the one in usage, as this can affect results. And one last point: To get really meaningful results, it's best to flow with a big pressure drop across the intake at low lift (up to 100 inches H2O) and low pressure at high valve lift (about 15-18 inches H2O).

Now, just so we are all clear on this: Wet flow testing does not necessarily deliver results in cfm. We are not measuring the flow but the state of the mixture and its ability to have minimum rivulets and maximum dispersion as it enters the cylinder. In short, it's all about the combustible quality of the mixture. Few people are likely to know this better than those whose efforts have aspired to the development and building of championship winning Pro Stock engines, and this is where Dart comes into the picture.

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This is the business end of the big Dart wet bench. Two huge air/fluid separators along with two big electric motors drive pumps that can simulate the airflow of even the biggest of blown engines.

If you ever meet Dart's boss, Dick Maskin, and penetrate his leather-like personality, it will become very clear right at the get-go that his whole goal in life is going faster than the next guy-at almost any cost or effort needed. As a Pro Stock champ, Dick understands the value of wet flow testing, but a Pro Stock engine with its two four-barrel carbs, a tunnel ram intake, and a highly developed head along with a 7000-10,000 rpm power band is an easier animal to deal with by far than a single four-barrel on either a single or two plane intake. Add to this the high performance engines that most of us deal with that have to operate satisfactorily or better, from idle to anywhere from 6,000 to 8,000 rpm, and a more complex situation by far emerges.




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