Cylinder Heads - Gone Platinum
Dart's New-Style Pro 1 Head Delivers at the Dyno
From the February, 2009 issue of Chevy High Performance
By John Nelson
"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.
Our 383 test mule needed a...
Our 383 test mule needed a bit of attention before its latest round of dyno duty. Our first order of business was to install one of Moroso's new 3⁄4-inch inlet, high-volume oil pump/pick-up combos. The pick-up location was spot on.
We then bolted on the appropriate...
We then bolted on the appropriate 7-quart pan--with trap door and kickout--for our late-model, one-piece main block.
Our head gasket du jour was...
Our head gasket du jour was Fel-Pro's PN 1003, which has a 0.041-inch compressed height, same as our original set.
During this stroker's last...
During this stroker's last dyno dance, a rocker arm came loose and we bent a pushrod. Accordingly, we installed a set of Comp Cams one-piece Magnum pushrods for this test session.
Fel-Pro also kept us well...
Fel-Pro also kept us well supplied with intake gaskets. Dart specifies PN 1206, which has a 1.34x2.21-inch oarifice, for all three of the heads we tested.
Our two sets of aluminum heads...
Our two sets of aluminum heads required a long-reach, gasketed spark plug. A set of Denso Iridiums, PN IQ24, fit the bill.
PLATINUM One result of Dart's...
PLATINUMOne result of Dart's wet flow bench investigations was a major combustion chamber redesign for the Pro 1 Platinum-series heads. The spark plug is now located as high as possible within the chamber, promoting more-efficient combustion. "The flame only has to travel one way," says Dart's Tony McAfee, "rather than both up and down." The long side of the chamber (arrow) has also been redesigned to further unshroud the intake valve...
PRO 1 ..."The way the combustion...
PRO 1..."The way the combustion chamber is shaped can improve air/fuel distribution around the valve," according to McAfee. The Platinum heads also come with back-cut valves, which helps low-lift flow and fuel shear on the valve.
Visually, the biggest difference...
Visually, the biggest difference between the old Pro 1 heads and the new Platinum version (front) is the absence of an exhaust crossover passage. "It was meant to help warm up the carburetor in cold weather," says McAfee. "We've found that it's not really used anymore, so we eliminated it during the redesign." (arrows pointing to both)
PLATINUM lthough the differences...
PLATINUMlthough the differences between the new and old ports are subtle, the wet flow process did lead to several changes. Entering the port, the pushrod wall is now "more of a radius," according to McAfee, rather than a flat spot. "Before, the mixture just slammed into the wall," he elaborates.The short turn radius has also been massaged. "We found there were gains to be made in the short turn approach, the way it drops off, and the actual height of the area," says McAfee.
PLATINUM An alternate view...
PLATINUMAn alternate view reveals another major difference between old and new, specifically the revised valveguide area. The vanes found in the new casting (arrow) help guide the air/fuel mixture into the chamber. If you think you see evidence of CNC work in the throat and bowl area, you'd be right...
PRO 1 ..."Even though these...
PRO 1..."Even though these are as-cast heads, each essentially gets a CNC bowl blend," explains McAfee. Although production tolerances are minimal, this treatment negates any variation--and provides performance benefits.
On the exhaust side, the visual...
On the exhaust side, the visual differences between the previous Pro 1 and the new Platinum iteration (front) are more obvious. The radically redesigned exhaust flange area is easier to cast than that on the old head, but this isn't an issue of mere expediency. "This new head can be ported to the point that it's like a race head," McAfee observes. "So we didn't want to limit people's choice of headers." Also note the difference in spark-plug location (arrow) compared to the older head.
PLATINUM Though the differences...
PLATINUMThough the differences between the old and new exhaust ports aren't as striking as those on the inlet side...
PRO 1 ...the new shaping around...
PRO 1...the new shaping around the valveguide is evident, as is the CNC work in the bowl.
PLATINUM Dart paid a great...
PLATINUMDart paid a great deal of attention to the valve-seat area when creating the Pro 1 Platinum head. "A three-angle valve job used to be common," McAfee explains, "but now production heads have a five-angle valve job." One benefit is that the venturi is moved farther away from the valve....
PRO 1 ...More importantly,...
PRO 1...More importantly, each angle is a shear point, which helps to reintegrate liquid fuel into the airstream. "The valve seat is the last chance the fuel has to be picked up and thrown back into the airstream," McAfee explains.
Dart's wet flow process uses...
Dart's wet flow process uses a solvent with the same specific gravity as gasoline. Under a black light and viewed through this plastic cylinder, the flow behavior of the air/fuel mixture becomes strikingly apparent.
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.
|GOING WITH THE FLOW |
|Dry Flow (@ 28 inches of water) |
|Pro 1 215||Pro 1 215 Platinum |
|Lift (inch)||Intake (cfm)||Exhaust (cfm)||Intake (cfm)||Exhaust (cfm) |
|0.200||128.0 ||114.8||144.1||107.0 |
|0.400||230.5||165.8||228.2 ||166.4 |
|0.700||260.9||191.3||268.2 ||199.9 |
|Wet Flow (@ 55 inches of water) |
|Pro 1 215||Pro 1 215 Platinum |
|Lift (inch)||Intake (cfm)||Fuel (lb/hr)||Intake (cfm)||Fuel (lb/hr) |
|383 STROKER SPECS |
|Displacement||384.6 ci |
|Bore x Stroke||4.040 x 3.750 inches |
|Rotating assembly||Speed-O-Motive cast crank and forged rods |
|Pistons||Mahle forged |
|Heads||Dart 215cc, 72cc chamber |
|Intake manifold||Dart single-plane |
|Carburetor||Holley 750-cfm Street HP |
|Distributor||Pertronix Flame-Thrower |
|Camshaft||Comp Cams hydraulic roller |
|Valve lift||0.520/0.540 inch, intake/exhaust |
|w/1.6 rockers||0.555/0.578 inch, intake/exhaust |
|Duration at 0.050||236/248 degrees, intake/exhaust |
|Intake centerline||108 degrees |
|Lobe separation||113 degrees |
|DYNO DETAILS |
|Headers||13/4-inch Hedman long-tubes with 18-inch extensions |
|Fuel||91-octane unleaded |
|Jetting||75 primaries, 80 secondaries |
|Timing||37 degrees |
|Iron Eagle Platinum |
|Max torque||464.2 lb-ft @ 4,600 rpm |
|Max power||463.9 hp @ 5,900 rpm |
|Average torque||425.4 lb-ft |
|Average power||335.8 hp |
|Pro 1 |
|Max torque||473.1 lb-ft @ 4,700 rpm |
|Max power||479.7 hp @ 5,700 rpm |
|Average torque||432.3 lb-ft |
|Average power||342.2 hp |
|Pro 1 Platinum |
|Max torque||483.8 lb-ft @ 5,000 rpm |
|Max power||503.2 hp @ 6,000 rpm |
|Average torque||441.5 lb-ft |
|Average power||351.0 hp |