Have you heard? The old rules about cylinder-head flow are changing. It's not strictly about airflow anymore. If you're serious about making horsepower or at least knowing what the big dogs are doing to spin that horsepower meter, the new mantra is: get wet.
Wet-flow technology is where it's happening in the cylinder-head world. If you think about it for more than a moment, the concept makes perfect sense. Intake ports flow fuel along with air regardless of whether the engine is carbureted or fuel injected. The sharp cylinder-head designers have started looking at creating intake ports and combustion chambers that mix fuel more efficiently with air, and the results appear to be impressive.
Dart Machinery is the first company we're aware of to apply this wet-flow technology to off-the-shelf cylinder heads, starting with its Platinum line of iron small-block Chevy cylinder heads. After witnessing Dart Machinery's custom-built wet-flow test bench in action, we couldn't get back here fast enough to write about it. This is the future of cylinder-head development, and Dart is leading the way.
What is Wet Flow?
The concept is simple. If we're really going to make more power, we need to know what happens to the fuel once it is introduced into the cylinder head and especially what happens as that air/fuel mixture blasts past the intake valve on its way to the cylinder. Well over 20 years ago, high-performance automotive scribe Jim McFarland's tech stories began discussing the concept of the "quality" of airflow into an engine, emphasizing the importance of properly conditioning the fuel as it entered the combustion space.
A few years ago, Joe Mondello and his partner, Lloyd Creek, developed the first commercially available wet-flow bench using an industrial solvent similar to gasoline in specific gravity that could be used to trace fuel movement as it traveled past the intake valve and into the cylinder. Mondello's wet-flow bench adapter is designed to be used with the SuperFlow 600 flow bench. The guys at Dart Machinery used many of the Mondello concepts but built their own massive flow bench specifically to move air at much higher Pro Stock-style flow rates. While the SuperFlow 600 bench can achieve flow up to roughly 600 cfm with large ports at 28 inches of water test depression, Dart's new bench is capable of a massive 55 inches of test depression with even the largest of Pro Stock heads flowing at valve lifts in excess of 1 inch. Owner Dick Maskin is still heavily involved with NHRA Pro Stock engine development, and while this bench was originally intended to help in Pro Stock cylinder-head R&D, the eventual goal was also to use it to improve the power potential of Dart's own line of small- and big-block street and race cylinder heads.
There is no high-performance cylinder-head crystal ball, but this black light dance of air
This is the bench that Dart built. The guys spent more than a year building and developing
Dart also uses its SuperFlow 600 and the latest 1020 dry benches to develop intake and exh
Any bench that can pull 55 inches of water test depression at 0.600-inch valve lift on eve
Dart designed its bench to simulate a Pro Stock-style air/fuel ratio of 13.7:1. According to Dart's cylinder-head specialist, Tony McAfee, once the bench was operating, Dart directed its efforts toward port changes that would increase fuel flow without sacrificing airflow. The other half of Dart's wet-flow R&D concentrated on port changes that would introduce the fuel into the cylinder in the most homogeneous fashion possible. In other words, McAfee and his team worked on moving as much fuel as possible (while maintaining a constant air/fuel ratio), yet working to mix the fuel with the air as evenly as possible. This is much easier to describe than it is to achieve.
Dart's first attempt at wet-flow development began with a redesign of the original Iron Eagle castings. "What's interesting is that often you won't see a big difference in airflow on a dry-flow bench between the Iron Eagles and the new Platinum heads," McAfee said. "The difference is all in the wet flow." Dart is now taking the next step of completely redesigning its line of Pro 1 small-block Chevy aluminum heads that will be sold under the Speed Flow Technology line. While much of what the Dart team has learned about wet flow with the Platinum line will be incorporated into these heads, there's bound to be some new stuff included as well, especially when it comes to combustion-chamber shape.
Our testing of both heads on a dry SuperFlow 600 bench proved out McAfee's statement, since the comparison of the intake airflow numbers between the older Iron Eagles and the wet-flow-developed Platinum series of iron Dart heads reveals virtually no change in the numbers.
New versus Old
The photos of the comparison of the Platinum heads to the Iron Eagles point to some interesting differences. With the intake valves removed, the vanes in the intake port are the most obvious. But more subtle changes include moving the spark plug in the Platinum head much closer to the center of the combustion chamber. Ideally, the spark plug in any engine should be placed in the geometric center of the cylinder. With Hemi engines, this is easy, but with Wedge-style engines, it's much more difficult. Placing the spark plugs closer to the center should have the effect of reducing the amount of ignition lead the engine requires.
Also notice how the combustion-chamber wall on the far side from the chamber has been laid back. This tends to coincide or line up with the long side of the port where a majority of the air and fuel move past the intake valve and into the cylinder. Angling the chamber wall away from the intake valve creates that heart-style chamber shape, but the reason is to allow the air and fuel to exit the intake valve with as little shrouding as possible.
Much of what constitutes wet-flow development is a mysterious blend of objective test numbers and a voodoo-like subjective interpretation of fuel patterns in the cylinder. It's like some kind of weird combination of internal combustion automotive research done with black lights and tarot cards. As you can see by the comparison of the photos of the Iron Eagle and Platinum intake ports, there are subtle differences in the flow patterns. Keep in mind that our photos are taken as extended time exposures of around eight seconds. This was the only way we were able to capture what is a very dynamic situation in very low light conditions.
Note how the Dart development team moved the spark plug in the Platinum chamber (below) mo
McAfee clued us in on what to look for on Dart's big wet-flow bench, and it didn't take long to see some significant differences in flow patterns between the older Iron Eagle heads and the new Platinum Speed Flow technology. The goal with any intake-port development, especially in regard to wet flow, is to design the port so the fuel is vaporized or mixed with the inlet air stream as uniformly as possible. This is difficult to accomplish because even the tiniest fuel droplet has significantly more mass than air, which means it is much easier for air to turn a corner or move around a valve seat than fuel.
The idea behind wet-flow development is to make it as easy as possible for the fuel to remain in suspension with the air. In a poorly designed head, the fuel will tend to collect as a series of small rivers of liquid that stream into the cylinder. Large droplets of fuel take longer to burn and burn incompletely as compared with very tiny spheres of fuel that burn very quickly and more completely. This means the smaller the droplets within the air stream, the less fuel is required to make the same power. It also means a leaner air/fuel ratio for the same (or more) power. This is why the Pro Stockers can make best power with an air/fuel ratio of roughly 13.5:1 instead of 12.5:1.
Since these smaller fuel particles will burn more quickly, a well-designed intake port and chamber will result in an engine that requires less timing to make the same power. Roughly 25 or 30 years ago, it was common for a small-block to require 38 to 40 degrees of total timing to make best power. The latest Gen III GM small-blocks now routinely make best power with less than 30 degrees of total timing. When it comes to ignition timing, less is better than more.
Looking at the photos of the Platinum compared with the Iron Eagle head, you should be able to see how the Platinum head introduces a much less defined and more evenly distributed air/fuel stream into the cylinder. The goal is to create an air inlet stream where the fuel is completely vaporized and integrated into the inlet air stream. When, or if that happens, you can expect power to take a significant leap forward.
In this dry-flow test performed on a SuperFlow 600 flow bench, you can see there is very little difference between the Iron Eagle and Platinum intake ports, each with 2.05-inch intake valves. Both heads were flowed at a 28-inch test depression on a 4.060-inch bore diameter.
|Valve Lift ||Iron ||Platinum ||Iron ||Platinum |
|Eagle ||Intake ||Eagle ||Exhaust |
| ||Intake ||Exhaust |
|0.100 ||65 ||64 ||59 ||57 |
|0.200 ||129 ||128 ||112 ||111 |
|0.300 ||182 ||180 ||139 ||140 |
|0.400 ||226 ||221 ||166 ||172 |
|0.500 ||258 ||253 ||178 ||189 |
|0.600 ||255 ||273 ||186 ||198 |
Wet-Flow Test Comparison
215 Iron Eagle 112.6 lbs/hr fuel flow rate215 Platinum 115.7 lbs/hr fuel flow rate
Difference: approximately 3 percent
This photo shows how the intake port vanes direct air and fuel toward the center of the bo
Since the chamber is very much an extension of the intake port, note how the heart shape i
This is a shot of the wet-flow characteristics of the Iron Eagle port. Note how there is a
This is a photo of the Dart Platinum head at the same valve opening and test depression. D
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