Let's face it, aside from the Wenzler Super Chiefs, there really are no other serious race heads for Pontiac engines. Sure the Edelbrocks are fine to a point when ported past the approximate 280 cfm that they flow out of the box, but guys who want to run in the 7-second naturally-aspirated door slammer club or possibly push toward 6s need a bit more. And even the Super Chiefs need serious porting to reach 400 cfm on the flow bench. Don Johnston, owner of DCI Motorsports in Mogadore, Ohio, has recognized the need for such a cylinder head and has been working on one for 7 years and is finally close to actually producing it. His new Tiger head at first blush seems to possess all that is required to make serious horsepower.
Though still in the prototype stage, the head that HPP photographed and the ports that were tested show great promise. DCI states 400-plus cfm out of the box on the intake side and 450-plus cfm with porting and the head delivered 400-plus cfm as you will soon see.
Current production plans include casting at Boose Aluminum in Reamstown, Pennsylvania, where each head will be X-rayed to eliminate potential fracture or porosity problems before they are sent to the customer. Accuform Manufacturing in Youngstown, Ohio, is slated to handle the machining of the heads and DCI will do the port cleanup, valve job, and assembly prior to sale.
The Tigers will be sold in two basic form-standard exhaust port height and raised exhaust ports. The first will retail for $5,550 and the later $5,850. What comes in the box will be a set of assembled heads including, guides, valves, valve springs, retainers and locks-ready to bolt on. And DCI is planning to have these heads available by the time you read this story and hopefully we can follow up with an engine build featuring them. But before you open the checkbook, let's discuss the philosophy and engineering that were applied to this effort and answer many of your questions before you ask them.
Don Johnston owner of DCI...
Don Johnston owner of DCI Motorsports proudly displays his new Tiger cylinder head on his SF-600 bench. Note the radiused air inlet used for flow testing and the trick Comp Cams flow bench valve opening fixture.
Production versions of the...
Production versions of the Tiger heads will be cast from T-356 aircraft-grade aluminum and heat-treated to a T-6 rating. These heads should weigh approximately 40-45 pounds bare, which compares to approximately 60 pounds for an iron head. Exhaust bolt holes will be Heli-coiled.
The Tiger head is compared...
The Tiger head is compared with a #48 D-port. Since this is a prototype, each intake port was worked differently. The port on the far left has been cleaned up to as-sold condition. This is the port that we flow tested. The center ports are as-cast and the end port on the right has been mildly ported to further explore the head's potential. Intake port volume is 310 cc as compared to the stock #48's 170 cc. Note the intake bolt holes on production heads will be repositioned to provide better gasket clamping force when used with spacers.
Grilling DCIWill Tiger heads bolt onto production blocks?The bolt pattern is stock for that purpose but the minimum required bore size due to the exhaust valve placement is 4.25 inches so the Indian Adventures block is recommended but you can use hard block in a factory block and bore to 4.25 inches. Another option is to reduce the exhaust valve size to 1.75 to allow for a smaller bore.
Which intakes can be used?An Edelbrock Victor or a Warrior can be used with spacers provided by DCI, which is working on its own intake as well. Don recommends, however, a sheetmetal tunnel-ram with Tiger heads.
How does the oil return from heads to the pan?Though not shown in the photos since the head is a prototype, oil returns will be machined into the head but the head will also be drilled for oil return lines at the back for quick return to the pan. Don recommends you use the return lines only and plug the others to reduce windage.
What about the water passages?Again, since the head is a prototype coolant passages are not present yet. Don says that he has designed the water passages to include center water ports to help reduce the heat buildup normally found in the center ports because they are so close together. This will greatly reduce head gasket failure.
How much can they be milled to reduce the chamber size?Since the deck is .750 inch thick, it can be flat milled .170 or angle milled .230.
What are the ribs for on the exhaust ports? Are they for cooling? Are they for strength?No, Don says they're just so you know which heads you are running when they are on the engine-shrewd marketing.
On the left is the inside...
On the left is the inside of the port as it will be prepared for each customer. Notice the work around the valve guide and into the throat. The intake port is raised 1-inch over the factory position and its opening measures 2.600 inches tall x1.300 inches wide as compared to a D-port at 2.050x1.100 or a Ram Air IV at 2.200x1.100.
Though tough to see here,...
Though tough to see here, the Tiger head (top) boasts the longest short turn of any Pontiac head at 1.500 inches (left) compared to the factory head at .500 inch.
Though tough to see here,...
Though tough to see here, the Tiger head (top) boasts the longest short turn of any Pontiac head at 1.500 inches (left) compared to the factory head at .500 inch.