Horse power drop using early A 273 manifolds

pishta said

It may not be the 273 rear firing manifolds killing it, but the F'd Y-pipe they used off of them, that kinked 90 was nasty! Then you had this..and that. Although it worked pretty good for a 273. Pics courtesy of @cosgig

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If that's a NOS or original HP head pipe, there were no mandrel bends back then. That design is very efficient. With that restriction it chokes the passenger side down through the pipe like the drivers side does through the manifold. LOL Even the HP 340 manifolds choke down around the steering column but not as much.