1951 Pontiac STRAIGHT 8 Split Exhaust Manifold??

I want to run true duals into side pipes on my Pontiac and I need some guidance.

I couldn't find a thread on splitting a stock pontiac manifold, only buicks and chevy 6's.

Does anybody have any pointers, pictures, descriptions, advice, no-no's, references, and what-not about this venture?

Ive been told you cant weld cast iron?

Any help would be greatly appreciated.

Thanks guys

-Aaron

 

A few years ago I made duel headers and 4 barrel intake for a straight eight Pontiac. It sure ran good.

 

The exhaust manifold casting is actually split front and rear internally, with both halves dumping into the same outlet/heat riser setup. You can take advantage of the fact that the internals are split and just come out the top to give your engine duals. Stubs are brazed, not welded, into the casting, set into it about 3/8'' to provide support and keep them from cracking off with engine vibration. Photos attached.

 

thanks for the help Greg, this may help. Did you notice any improvement with the split manifold?

 

Noticeable, running Smithy's mufflers. If I had not been using the dual intake I would have centered the new outlets directly over the center of the front and rear manifold halves. I had to push the outlets a bit forward and back to clear the carbs. The outlets are 1 3/4", which is the width of the manifold casting. Let me know if you need more info. Good luck with your project.

 

What is the crank configuration, 4-4 or 2-4-2 (i.e. Packard style)?

Splitting the exhaust the other way to the crank configuration will give a conventional V8 sound. Splitting the exhaust the same as the crank configuration will give a single-plane crank V8 or inline sound.

 

Now there's some excellent info! That's what Hamb's all about, and input from around the world. Looks like front exhaust pipe is a little too close to carb/float bowl, just sayin'.

 

You are right. Ran out of room to move the exhaust stub outboard and still keep it close to the front half centerline. Exhaust wrap is the answer.

 

do you have pics of your fab work id love to see it im at that stage of creating my own

 

is that an aluminum flathead intake welded up at bottom and cut on each side

 

35flatty, send me your email address and I will send you photos. Best wishes with your build. Greg

 

Johnny Franklins Mufflers in Santa Rosa, CA split the exhaust manifold on my '47 Streamliner 8 for $120 . It exits out the bottom into 2, 2" pipes with flanges to bolt the head pipes to . From there they go to 80" lakers or 12" glasspacks. It sounds real mellow and is easy to uncap and makes alot of noise when opened up.

 

1951Streamliner what did you end up doing? Does anyone else have any pictures of how they did their Pontiac straight 8 dual exhaust?

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