So my wife, the purist, wants duals with Smithy's on the '57 Poncho. This is a miracle in itself, since she always wants everything STOCK. Anyhoo, how the hell do you put duals on these bad boys, if they have the factory single exhaust? The driver's side manifold exits to the front of the car, with a funky crossover going under the engine, to merge with the right side head pipe. It looks like a helluva tight bend to run a pipe down and back, but doable. Is there any other manifold I can use that is a center, or rear dump? Also, anyone know a decent exhaust place in the Seattle area that doesn't want your firstborn for a set of duals? Thanks, Jake
Now you know why the '57 Pontiacs with factory duals had a two piece LH manifold; the piece you've already got, and a second casting that resembles a piece of elbow macaroni that directed the exhaust rearward to meet the front pipe. Center dump manifolds came into use in '59, but that's also when the ports were redesigned, so you'd have to look at one and see if it would seal on the '57 heads. Also, you may run into crossmember interference with the center outlet.
I have the problem running down the drivers side back and got this info from a web site on project40 I think it will work for me but also could be an ideal you could use. The guy used pvc pipe to mock-up the routing, so you can take the pvc up to a shop and they can dupicate your pipes and you install and save bucks. The muffler is a flowmaster series 50.
Thanks for the tips, guys. If anyone has one o' those factory cast elbows, I've got cash. Otherwise, the job looks way too complicated to spend on a four-door car. Guess I'll just wait 'til the SBC gets dropped in to run duals. KIDDING!
I had a header for a mid-60's GTO/Lemans application and it fit up to a '57 head fine. Any D-port manifold aught to fit on the 347 - This is the problem with '55-'57's - there is not a lot of clearance around the steering for a conventional dual setup. You need a manifold that dumps real close to the motor, but it can't be too close because the starter is on that side. It can be done, but it takes a real patient tubing bender to make something fit in there (I'd do it in stainless just so I never had to do it again). I've wondered if something similar to what the guys putting Chevy v8's into the 49-54 cars use will work - instead of the 267/305 manifold they use, a 301 manifold from the Pontiac versions of the same cars. Never saved the ones I had to see how they measure up. So far have yet to run into anyone who's tried. Seems like you'd need it from a 78-81 Gran Prix or Lemans.
Just pulled out the shop manuals and from the pictures it looks like the left manifold is similar enough to the right one to make using two right ones a possibility (with the heat riser butterfly removed and provided you can even find another one of those). You might have to change the angle slightly or or shorten up the dump a bit, but nothing a chop saw disc in a 4" angle grinder, preheating, and a little high nickel rod wouldn't cure.
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