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Dyno tests on my RAIV 400 motor stingy dyno though muffler my HO and a 800cfm 73 SD SR Q ket , a 3310 holley on a T1 and then a T2 all dynoed the same HP. Single planes lower TQ at bottom end. Q jet on the T1 at the track killed bottom end even with a 4000 stall and 4.56s. Gained a couple of MPH but lost so much 60 ft ran slower.

First E head 455. My cleaned up 72 HO SR intake, UD 259/262 solid roller through 3" exhaust-swap at track from a 73 SD QJet reworked by the Carb Shop Brad Urban swapped WITH an open adapter a Demon 850 DP(when they were first out and good) idled better out of the box and picked up 0.3 seconds! So much for an adapter killing things. Later swapped on a single plane T2 and the Demon idled even better and picked up enough to kill the torque convertor and trans(stock rebuilt 350). Not an at the track swap so can't tell you identical exact increase. But with a new looser TQ convertor asnd built TH 350 picked up 0.75 seconds! That was about a 550-575 HP motor.

I have some posts and pictures on my Repop RAIV intake and it took a second one to get OK ports but they still needed weld and a lot of grinding to even get close to a FelPro 1233 gasket! But it is pretty close now.

So all depends on what you are trying to do I do think a stock intake is getting to be the "restrictor" at about 500 HP. Why even back in the day of unported heads in SS they used a Nash or even the Torker 1!