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split manifold
https://www.slantsix.org/forum/viewtopic.php?t=50193		 Page 1 of 1
Author:  chucksrodgarage [ Fri Oct 26, 2012 6:45 pm ]
Post subject:  split manifold
any pro's and cons on splitting a stock exhaust manifold? it was done a lot years ago,and on my old school 41 plymee with the slant, i thought it would be a good choice. i'm a diy guy, otherwise, i definately would go with the dutras.
thinking of just cutting a slot between 3 and 4, and brazing in a piece of 1/8" plate, and adding another outlet.
any pro's and cons appreciated.
Author:  ceej [ Fri Oct 26, 2012 7:12 pm ]
Post subject: 
In effect you'd be making your own version of the Dutras. A lot of folks have done just that. All the benifits of better exhaust flow. Keeping the rear connected to the stock outlet is the best way to go. Keep your carb heat, and maintain as much clearance around the starter as possible.

CJ
Author:  Doc [ Mon Oct 29, 2012 9:22 am ]
Post subject: 
No reason why you can't make your own split exhaust manifolds... as long as you know how to successfully weld cast iron together.
DD
Author:  chucksrodgarage [ Mon Oct 29, 2012 2:12 pm ]
Post subject: 
that's one of the things i hoped to get feedback on . welding verses brazing. i wouldn't want to attempt to weld them myself, but i have a machine shop friend that definately can do it, but i have done a lot of brazing and silver soldering in my time, and know i could easily do that as long as i give it a long cooldown time buried in sand or likewise.
i have all the fabing done right now but haven't got to gluing things back together yet.
thanks for the reply.
Author:  Doc [ Wed Oct 31, 2012 4:23 pm ]
Post subject: 
Brazing cast iron is easier but questionable for an exhaust manifold, seeing that the manifold can get hot enough to weaken the braze joint, causing you work to "fall apart".
(most brazing filler rods melt in the 1300 to 1500 (fahrenheit) temp. range)

I have never taken temp. measurements but I have seen SL6 exhaust manifolds glow a dull red, in the dark so I am sure it is well above 1000 degrees F when doing that.
DD
Author:  chucksrodgarage [ Wed Oct 31, 2012 6:40 pm ]
Post subject: 
yes, i don't like surprises, i have never heard of a brazed manifold melting out the braze joint, but the temps would be very close at dull red. should never reach those temps unless timing is way off, or under a heavy load for quite a while, but i talked to the machine shop friend of mine, and he said he would weld it up for me with nickel rod. this guy is real good, and very reasonable. better safe than sorry.
Author:  Doc [ Thu Nov 01, 2012 9:05 am ]
Post subject: 
The braze joint does not "melt-out" but instead, breaks apart in a way that looks like it was soft, at the time of failure.
Truth is, I have successfully used brazing to seal "capped-off" manifold rear sections for Dutra Duals.
I screw-down the cap plate first, then braze the joint "seam". Works fine, mostly because there is little to no load on the cap and the brazed joint is located out of the direct exhaust gas flow path.
I would not use braze on a joint attaching a new outlet flange onto a exhaust manifold "body"... even if I screwed it down first. There is a lot more heat and load in that application.

These days, I weld all my cast iron exhaust manifolds with nickel rod (NiRod 99) and get great results, using that process and filler material.
Good prep and fit-up, then pre-heating & slow cool down of the work-piece are all important steps.
DD

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