Yes it does come out at a little bit of a rectangle & then go round, but if I'm thinking correct the reason for teat is velocity. The port come out like a trumpet as it opens up to the round port. I would think that would give it some pick up speed when it come out like that. I'm not an engineer but just looking at it I would think that was what the designers were trying to do. Plus if you look into the port it gives you a bunch of room to open it up for more flow. The reason I say this is if you look at the SD head it looks like the RAIV head but opened up more , & then if you look at the heads i have which are the Eldo. alum. head which were designed from both the RAIV heads & the SD heads. My Eldo. alum. heads can flow up to & more then 340 cfm with work & I would bet that the SD heads can be done to do the same. As can the RAIV heads be done almost as much as the others. You have to remember that GM even in 69-70 were still watching the designers close so they didn't go to big on the HP ratings of the engines. Maybe thats why the RAII heads were 1:55 & the RAIV were 1:65 rockers. They were just building up to a certain point for HP but didn't go all the way so they wouldn't get shut down. You never Know?????? But my Eldo. heads are a great set & just bolting them up to a 400 or 455 give you a great boost from the iron heads. Because of there design. I think so. Heres a big what if, what if the Pontiac guys had the alum heads from Eldo. back then. How fast would the 69-70 's been then. WOW !!!!
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