I have been looking at the AFE exhaust you can purchase and wondered why they pie cut their bends. I’m assuming that it must be the overall cost that keeps them from buying a mandrel bender. I started estimating the cost of this project, if I purchased pre-bent stainless tubing. In the beginning I did not know how I was going to make the down/outlet tube. So with tubing cost, flappers, Misc. stainless, hose and hose clamps, I figured materials would cost approx. $250. Part of the reason for the higher cost, was that my boat did not have the plastic standard exhaust flappers, it had the 4” stainless steel turndown tips. As I progressed with the project, I added the muffler delete, upgraded the clamps and changed to a 2 hose connection instead of a 4 hose connection and this made me buy extra tubing. Because of these changes I have $410 in materials in it.
My muffler connections are 3 1/2”, so all I’d did here was purchase (2) 45 degree 3 1/2 mandrel bent SS tubes and cut one end off to make it fit. I just had to rotate my SS exhaust outs on the manifolds a little and then rotated my rubber transom connect hoses a little also.
I then made my thru-transom connect pipes. 4” long by 3 1/2” tube welded to a 6” od x 3” id outer plate. I then welded my 8” long by 3” tube to the outer face, orienting them to point toward each outer exhaust. This outer tube is where I installed the flappers.
I then welded the (2) 3” 90 degree tubes (with longer leg on each). After this, is when I decided to make a 2 hose connection instead of the 4 hose connection. so I had to purchase (2) 3” 15 degree tubes and weld them to the ends pointing toward the thru-transom connectors. The down/outlet tube was originally going to be a 3” oval tube with no modification. Then my buddy said he could make some molds from wood that we could use in the hydraulic press and form the oval tube to make it round at the weld connection at the top and slightly v-shaped at the outlet end. It worked awesome. Then I studied some of the. AFE photos longer and decided to buy the 3 1/2” oval tube, made more molds and pressed it, then welded it to my upper tube. I then ground all my TIG welds smooth.
I spent a fair amount of time sanding and polishing (more than I wanted). I wasn’t going to install the flappers, but decided too, after deleting the muffler. On all the tubes that have a hose connection with clamp, I welded a small 1/4” round spot of weld that sticks up an 1/8” in 4 equal spots around the tube. This is to allow the hose to “grip” without pulling off. I actually got this idea from looking at my 4” turndown tips that I removed. I’m amazed how ridged this setup is, I can stand on the the outer tube and it barely moves. I have yet to test it in the water, so I might still have to modify it some.
All parts were sourced from Amazon, EBay, Stainless Headers & local hardware store.