Editing Pontiac V8 engine (section)
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===Port volume=== Then there's the port volumes. These heads have relatively small intake ports; the 6X-4 heads used on one 455 build were 158cc "stock" (these ports have also been measured at 153 cc), and they did not look to have been ported. After porting they measured 173cc. These stock sized ports would be like a ~ 125cc head on a 350 SBC. The comparison isn't as bad as it sounds because of the design of the Pontiac head/ports and the 30 degree intake valve angle, but the fact remains- they ARE small. Usually a stock or mildly reworked D-port Pontiac head doesn't need lift in excess of 0.480". That is a little past where maximum flow is reached but before any port stall occurs, given the rpm range of a 455. Combining that w/a duration @ 0.050" of around 234-236 degrees or so will be about right for a strong street engine that will run mid 12 second ETs at the drags and can be driven daily, anywhere, without issue, on 89 octane gas, and using a 2.73 to 3.31 gear ratio is all that's needed.
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