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Mechanical / Re: What is the difference between Round Port and D Port?
« Last post by nas t eh on Today at 12:02:41 AM »The list of Pontiac motors with round port heads is short,
1. 1968 400 RAII
2. 1969-70 400 RAIV
3. 1971-72 455 HO
4. 1973-74 455 SD
5. All the variants of the RAV
The round port heads of the first 4 on this list have larger (taller) intake and bigger better shaped exhaust ports with much higher flow characteristics. All also have the bigger 1.77” exhaust valves.
The V are different again with even bigger separate ports with the valves relocated in an IEIEIEIE arrangement instead of EIIEEIIE
If you are thinking of buying new aluminum heads even the D-ports flow very well out of the box and if bought set up from one of the big Pontiac shops can be CNC ported for only a little more to flow extremely well for street use. Round port aluminum heads have even more flow and more ported potential.
1. 1968 400 RAII
2. 1969-70 400 RAIV
3. 1971-72 455 HO
4. 1973-74 455 SD
5. All the variants of the RAV
The round port heads of the first 4 on this list have larger (taller) intake and bigger better shaped exhaust ports with much higher flow characteristics. All also have the bigger 1.77” exhaust valves.
The V are different again with even bigger separate ports with the valves relocated in an IEIEIEIE arrangement instead of EIIEEIIE
If you are thinking of buying new aluminum heads even the D-ports flow very well out of the box and if bought set up from one of the big Pontiac shops can be CNC ported for only a little more to flow extremely well for street use. Round port aluminum heads have even more flow and more ported potential.
