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View Full Version : 4A084 Custom Exhaust Headers Build



Bart
02-20-2017, 03:06 PM
In looking at the many different exhaust manifold builds on this forum, and the pictures of what many others have posted on the web, the field is wide open, on what has been built. ;stir;
so here is what I am going with.
I have liked where others have used 1" SS tubing.
so I thought I would give it a try
materials used
1. set up jig
2. 1" 316 SS tubing, with .049" wall thickness, with .91" ID & 1.008" OD
3. exhaust pipes from a Harley (a sweet 20.00 purchase from last summer)
4. assortment of homemade flanges

i ended up cutting one stub off of one off my 042 exhausts to get a measurement for the exhaust clamp, and measurements of the inside of the factory exhaust.
the factory exhaust diameter is .93" ID & 1.058" OD
the SS tubing is just a little smaller, .02" on the internal diameter. don't know how this will play out.
there are more than couple of different methods, to
to get the radius needed, the simplest way, would be to purchase a tubing bender. that would fit 1" tubing.
But with an 1" EMT bender, i bent a piece of 1" EMT into a 90, cut the radius in half, length-ways (see picture below) the SS tubing fit fairly snug in this. good enough to keep it from flattening out to much. and what little it did flatten, i was able to work the flat part out.
there has been a lot of discussion as to what length to cut have for the headers.
then I came across a picture in (Dan's Build) of the custom un-assembled headers that he purchased from Chucks, and i liked how they fit up and looked.
http://miniairboatassoc.com/forum/attachment.php?attachmentid=928&d=1333760957

from the picture I was able to get an good idea as to the length of the header pipes that was purchased.

I was wanting to keep the headers in one piece and not have a weld joint so close to the exhaust port. (any time there is a joint it will create turbulence)

thought about making a small bead roller. (well I still might fab something up later,now that i have my little lathe working)
but then i came across an add for some motorcyle pipes from Sweden that had something similar to a swagelok crimp
And that looked a lot simpler.

I really didn't want to cut up the factory exhaust to use the flanges, so i made some out of 1/4" flat bar.

On the Harley exhaust headers that i picked up last summer,
each had close to a 45 degree bend, that i used to join the headers together, and get it started pointing in the right direction. to fit them over the 2 header pipes, I started the oval shape with a vise, and did the final crimp with a cowboy clamp to get a good snug fit for the weld up.
tried used some stainless rod with my stick welder. but i couldn't get the heat range low enough. for the rod that i had on hand, after cleaning up the mess, was able to have a friend with a tig weld everything up in short order.
.
After the headers were welded and cooled off. when removed from the jig. the header contracted to a 5-1/4" on center, but the nice thing about SS tubing, I was able to message to back to the 6" on center.:razz:
I put a O2 sensor bung on both headers, (still working on getting an O2 gauge.)
but also i will use this to measure the back pressure.
there has been a few posts talking about this. the manual states that with using a manometer you should have 20" inches of water column, this would be close to .75 psi.
not a lot, if you are to use an pressure gauge. (I think I would need a 5 psi liquid filled gauge to even attempt taking a reading from a gauge, and i still don't know if you could get an accurate reading with the exhaust gases fluctuating.)
so I will probable go with a manometer, it will be simpler in the long run.

To restrict the backflow, I fabricated some flanges with holes ranging from 7/8" to 1-1/8" to slip in between the header outlet and the muffler.

The manufacture exhaust pipes coming out of the motor are at .93" ID, and the crossover pipe goes up to .96" ID.
I should have enough selection to get me in the ball park.

I haven't put the flanges on the headers yet, waiting to put the motor on a hull, with the mounting flanges that are on the headers, just to many variables out there, so some things will just have to wait.
just another item that i have been working on

Bart
02-20-2017, 03:10 PM
needed to add a couple more pictures
the brass ring on the bead roll and the header is the brass seat that seals the pipe to the exhaust port on the motor.

Corky
02-20-2017, 11:09 PM
Looks good Bart !!! It'll be interesting to see which size hole the engine likes...