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Tech Articles

Category 2 Big Block: 220cc to 299cc Intake Ports


 

GM Iron 290 Oval Head


This is a representative closed-chamber oval-port head. Even with its 50cc larger port volume, the small valves hurt airflow. This head continues to flow well beyond 0.700-inches of lift, which leads us to believe that larger 2.19/1.88-inch valves would help especially on the bottom end and across the rest of the board.

GM 049 Iron Oval Port


This Open chamber oval-port head saw use in a number of 402ci to 454ci big blocks from ’73-’84. Of the three stock iron oval-port heads we tested this one was the strongest. Again, like other production heads, if horsepower is your goal, larger valves are the way with these heads.

GM 702 Iron Oval Port


This is an example of an early 396ci and 427ci closed-chamber head used only in ’65 and ’66. This head virtually clones the GM 290’s flow numbers. While the 049 head flows much better it would drop compression two full points. The best set up here is to either give up some power and use the GM 702 head as a matching part number restoration piece or go with the better GM 049 head and Open chamber pistons to match.

Brodix OEFI Aluminum Oval Port


With a maximum flow of over 270cfm right out of the box and a "small" 255cc port volume, this Open chamber head is an excellent choice for making outstanding torque and reasonable horsepower. We’ve seen these heads ported and on a Lingenfelter dyno make as much as 650 hp on a 502ci big block. This head can be a serious street contender.

World Products Merlin Iron


This head is just what GM should have built for its Chevy enthusiast. Its design is very similar to the production GM heads but has been outfitted with larger valves. The small port volume makes for great streetable torque while larger valves accommodate all the extra flow these ports can handle. These heads do not come with any handwork to the bowls, which would help tremendously.

Dart Oval Aluminum


This head flows much like a larger rectangular port head up to the 0.500-inch lift mark. From there the rectangular port pulls away only because of its larger design. The E/I ratio of 75% was the best in this class, which tells us that this head would be ideal for an automatic transmission equipped street terror.

Edelbrock Performer RPM Aluminum


The RPM head features a large-volume oval port with a unique rectangular oval-port entry, or "roval" for short. This head sacrifices low lift efficiency just a little for its high lift flow numbers up around 0.800-inches of lift. This head would best work on pump gas 396ci to 502ci motors.

GM Performance Parts Aluminum


This head offers the highest average intake port flow and the highest peak flow numbers. The exhaust was very impressive creating an E/I ratio of 72%. This head would be best fitted on a big-inch street big block using a large cam that could take advantage of this head’s high lift flow potential.








 

   
 
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