The original Cummins exhaust risers that came with my Cummins 6CTAs take a 90° turn after exiting the turbo, but there is no way to safely point the exhaust toward toward my waterlift mufflers. The turbo would end up being on the low side of the system, and that’s bad news for wet marine exhaust–you don’t want water flowing back into the turbo and engine. So two years ago, I checked with several marine exhaust manufacturers about having custom exhaust risers made, with the dry section going as high in the engine room as possible before turning down with the showerhead pointing toward the waterlift mufflers. The estimates that came back were quite high–they averaged $5300 for both sides. So I held off on ordering a set until they were absolutely necessary. Well…we’ve reached that point now.
Oh, and those original, low hour Cummins risers are listed on my For Sale page.
While I was waiting, I found some brand new DeAngelo hard shell marine exhausts on ebay. They were advertized as being made for Cummins 8.3 engines, which is what I’ve got, and the price was right. So for the last two years I’ve toyed around with the idea of buying those and modifying them to fit my application. Over the holidays, a friendly commenter mentioned the ones on ebay, so I pulled the trigger and bought them. The thing is, while I’d been aware of them for two years and thought about how I’d modify them, I never really investigated the parts themselves. Turns out that was an expensive lesson in why it’s important not to make rash decisions just because somebody double-dog dares you.
While it was unfortunate that one of the risers arrived damaged, I wasn’t really concerned about the hard shell being damaged since I would have to cut it off to modify the riser anyway. The flange was a bigger concern. I contacted the ebay seller and let him know about the damage on the one riser.
But the biggest problem of all was that on both risers the showerhead and raw water inlets were too big. The original Cummins risers for these engines have a 6″ diameter outlet, and the raw water inlet is 1-1/2″. These risers had an 8″ outlet and a 2″ water inlet. Without thinking it through very much, I figured I could just use a reducer between the showerhead and the muffler. So while the return was being processed on the damaged riser, I got to work dismantling the good one.
Intuitively, I like the fact that these risers quickly increase in diameter after leaving the turbo. It steps from 3-1/2″ at the flange to 4″, then immediately up to 4-1/2″ where it enters the insulated zone and then up to 5″. After the 5″ 45° turn, it goes up to 6″ the rest of the way. It makes a very complicated part, but that big pipe must be good for lowering back pressure. Since my port riser will be longer and have more bends than the starboard, I was thinking that maybe the fat pipe will compensate for the additional back pressure.
The whole time I was dismantling the riser, I was focused on the task and not really thinking about next steps. After I had it cut up, I started looking into the parts it would take to make this riser work. It turns out there are reducers, but they’re somewhat expensive. Then I remembered I’d have to buy two stainless anti-crush rings that go inside the fiberglass reducers. Then I’d still have to buy the materials to modify the riser and pay somebody to weld them up. I’ve had bad luck with fabricators in this area, so there’s that, too. I was looking at no less than $600 more to make each riser which, when added to the purchase price, is getting close to the cost of just having a set of risers custom made.
It was around this time that I really started kicking myself for buying these risers. The ebay ad was misleading, but I should have contacted the seller to verify the dimensions. When I realized they were too big, I should have just sent them both back. But then, with my new-found understanding of how these risers are made, I started thinking about just buying all of the materials and making a set myself…
Next up in our 1969 Chris Craft Roamer 46 Refit: New Riser Materials