Blueprint provided by DCI Motorsports
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.
GRILLING DCI
Will 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.
Why is the short turn in the intake port so much longer in the new head as compared to factory?
According to Don, the longer short turn reduces the sheering effect that occurs when the turn is too short, which causes the mixture to push across the valve into the opposite wall of the port thereby not using the whole valve area. The longer short turn provides better flame propagation by creating more of a cone or funnel effect around the valve.
What does raising the intake port entry do?
It creates a straighter port to get a straighter shot to the valve thereby making more power and it keeps the fuel suspended longer. Fuel tends to drop out of suspension when making sharp turns Don related.
What does radiusing the port corners do?
"It helps promote velocity," Don explained. He also related that the 310 cc port runner is conservative as many big-block heads for other brand engines have larger port volumes like 360 cc or more. But the port size here is smaller to maintain velocity and produce more midrange power. That's also why the ports appear tall and narrow.
What does raising the exhaust port do?
In this case, it provides the 80 percent of intake to exhaust flow that many racers are taught is the optimal balance. Don believes however, that more power is made when that ratio is closer to 70 percent, which is just where the stock height exhaust ports generally flow.
On the heads with the stock height exhaust ports, why are round and D-ports offered?
This is so racers stepping up from D-ports won't have to incur the cost of new headers as well.
Do the round exhaust ports flow significantly better than the D-configuration as is the case on stock heads?
Don says that they probably do but he hasn't tested them yet. Since the same casting is used for both, if a racer buys the D-port Tigers and decides that he wants round ports, all he need do is gasket match the exhaust ports to the round port headers.
Don Johnston would like to thank is wife Cindy and the guys at the shop for all of their help in developing these cylinder heads.
Head Flow Testing The head was tested on a SuperFlow 600 flow bench. All measurements are at 28 inches of water. Outside temperature was 70 degrees, the flow bench temperature 115 degrees and the relative humidity was 62 percent. The test fixture bore size was 4.25 inches. Valve Lift Intake CFM Exhaust CFM Int/Exh Flow Percentage .100 76.50 63.20 82.61 .200 144.55 111.80 77.37 .300 207.97 161.00 77.41 .400 267.00 196.40 73.55 .500 315.95 230.20 72.85 .600 358.20 252.20 70.40 .700 388.05 264.30 68.10 .800 411.93 269.20 65.35 .850 417.90 275.20 65.85 .900 422.37 276.50 65.46
BOUNTY HUNTER
Want to earn some dough with Tiger heads? Don Johnston has put up a challenge to any customer who buys his heads. The first, to put a door slammer in the 6-second zone with his heads installed albeit with nitrous a blower or turbos, will collect a check for $5,000. He would also like to see a normally aspirated 1,000hp engine sporting Tiger heads on the dyno. For this, there will be a money prize as well. How much has yet to be determined. Contact DCI for the official rules and restrictions regarding these two offers. --TD
About DCI Motorsports Inc.
DCI Motorsports, Inc. opened its doors in 1983 and actually began as a carb shop. The principles in the business at that time were Don Johnston, his wife and partner, Cindy, his uncle John Ferguson, and his wife Seena. Soon thereafter, building carbs graduated to building engines. A few years later, Don bought out his uncle and not long after the business became dedicated to high performance Pontiacs. This progression led to designing and manufacturing engine parts, including valve covers and sheetmetal intakes, and gaining valuable experience building turbocharged, supercharged and nitrous engines. Today, the 2,000 square foot shop caters to any Pontiac from restored 13-second stockers to 7-second chassis cars and has a faithful following in Ohio. The facility contains a SuperFlow 600 flow bench and will soon have a Stuska dyno for engine testing. As this article depicts, DCI is currently undertaking its most ambitious project, producing aluminum race heads for Pontiacs, which will be followed up with a matching intake manifold. Customer cars in the above photo include this 428-powered, five-speed manual '68 Firebird owned by Paul Knapp that was about to leave for Power Tour. The bracket racing '75 Firebird with a 406 that runs 11.18 at 122 mph is owned by Rodney Spicer. The '81 Grand Prix with a transplanted 400 Pontiac engine belongs to Roger Roman and Don's old GP racer is on the other side. The tube chassis Bird owned by Jim Scott packs a DCI-built 455 engine, and runs 8.74 at 154 mph. --TD
