"Racing improves the breed," the old adage goes. But is change always for the good? That's what we set out to discover in this month's dyno thrash. In one corner, we had Dart's veteran Pro 1 aluminum cylinder head; in the other, we lined up the revamped version, the Pro 1 Platinum. The Platinum heads are the result of technology that Dart has been employing in its NHRA Pro Stock efforts, specifically a process known as wet flow technology. In short, a wet flow bench measures the flow of fuel and air--as opposed to just air--through a cylinder head. As a bonus, our 383 test mule was already wearing a set of Iron Eagle Platinum heads, so we threw them into the mix as well.
Wet Flow Basics
As you may have divined, the wet flow process allows a cylinder-head designer to look at how the air/fuel mixture behaves when routed through a head and into the combustion chamber. "We're not just looking at dry flow, we're looking at wet flow," says Dart's R&D manager, Tony McAfee. Given that an internal-combustion engine needs both air and fuel to perform, it makes perfect sense. As we've explained elsewhere, much of this process' advantage comes from being able to see how the air/fuel mixture actually behaves within a cylinder head and shape the ports accordingly. There are, however, other advantages.
"One thing I look at," says McAfee, "is whether a port design will maintain a constant air/fuel ratio." Tests are made at a predetermined ratio, 13.7:1. But the wet flow bench also measures the actual air (in cfm) and fuel (in pph) being used. "The air/fuel ratio with the most fuel makes the most power," McAfee tells us. Remember that the idea is to obtain a homogenous mix of air and fuel. "The fuel must be kept in suspension as much as possible," McAfee elaborates. With a better mix, more fuel is actually delivered to the combustion chamber, creating the potential for more power.
One other difference between a traditional dry flow bench and Dart's wet flow process is that the tests are made at 55 inches of water, rather than the 28-inch level we're all familiar with. "It's actually closer to the high-rpm depression (low pressure point in the cylinder) at WOT," McAfee explains. "Fifty inches is closer to a serious bracket engine, and a Pro Stock or Winston Cup engine is well over that. We need three 50hp engines to get there."
By the Numbers
Bottom line? The wet flow process has yielded a better-flowing head that makes more power. Period. The dry-flow figures show improvements in airflow, but the wet flow results really tell the tale. Take a look at the numbers. Considering airflow only, the old Pro 1 actually outflows the newer Platinum version in some areas. Add fuel, however, and the Platinum head is the clear winner, as shown in the airflow figures and as demonstrated on the dyno. We made a whopping 23.5 more horsepower, along with 10.7 extra lb-ft of torque, and interestingly, each peak occurred 300 rpm later than with the older Pro 1s. Average numbers also improved, however, checking in with an additional 9 hp and 9 lb-ft across the board.
One thing we didn't expect was the huge power difference between the Iron Eagle Platinum and the Pro 1 Platinum heads, which were both designed using the wet flow process. Then again, the iron heads didn't feature the valve-seat insert or any of the CNC bowl work found in the Pro 1 Platinum--or the original Pro 1, for that matter. The Iron Eagles made good power on our 383 mule, and they pack a lot of bang for the buck. But the benefits of the bowl work found in the aluminum heads were clearly demonstrated. Combined with the rest of this thoroughly revamped head, the results are striking. "It's a package," sums up Dart's McAfee. "No one thing alone can do it." Check out the numbers to see how the new wet flow-designed Pro 1 Platinums raise the performance bar.
Q&A WITH TONY MCAFEE OF DART MACHINERY
CHP: How did this redesign start, Tony? Tony McAfee: It was time to upgrade the Iron Eagle and Pro 1 heads, so what we did was take the old design and played with the wet flow process we've been using on our Pro Stock heads, looking to make a better mousetrap.
CHP: What are the advantages of the wet flow process? TM: You're simulating a running engine more closely than on a dry flow bench. An engine doesn't run just on air. When you add fuel, the whole airstream becomes heavier; it does much more than dry air.
CHP: Like what?TM: When you see the fuel run, it runs in streams. You see the vortices in the combustion chamber. And no matter what, fuel attaches to the port walls... It's gonna happen.
CHP: And you can actually see this on the wet flow bench? TM: Yes. It can be seen in black light, through a half port made of clear plastic. You can see everything the mixture does, where it's at, how it moves. We've been able to see many things we couldn't imagine.
CHP: So what have you learned so far? TM: The combustion chamber should be thought of as an extension of the intake port, and the way it's shaped can improve air/fuel distribution around the valve. The plug is also moved toward the exhaust port; it's now in the same place as a Vortec head. Flame travel is one of the big positive sides to a Vortec head. Most people think it's airflow, but that's only half of it.
CHP: What other areas have you found to be important? TM: The cross section of the port, for one. We've also worked on the short turn and the diameter of the throat. They need to be a specific area based on valve size. Also the bowl and valve-seat area. We want it to gather loose fuel, rather than let it hit just the back of the valve. Once it leaves the valves, you have to make the mixture keep moving.
CHP: Once you've seen how the air/fuel mixture acts on the wet flow bench, how do you go about achieving the results you're looking for?TM: It's trial and error, using traditional methods: epoxy, grinding, and welding. We do anything we can do to make it flow better. I'm still trying to teach myself how to influence the mixture flow.
CHP: Really? TM: Wet flow technology is in its infancy. I don't know half of 1 percent of what we'll know in a few years.