New Exhaust

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New Exhaust

Postby StevenD » Fri Nov 01, 2019 8:44 am

Another step in the right direction. This FRP elbow is my third try at getting this exhaust system back together. The first time the angle came out wrong, so I cut the hose, changed the angle of the elbow and added 6" to it. That made it too big to assemble in place so rather than cutting and grinding the original (no me' gusta), I built another, measuring 3x cutting 1x. Now I just need to modify the support brace for the new riser. Third times a charm right!
Steve D
M/V Kumatage
Hobe Sound, Fl.
GB 46 CL
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Re: New Exhaust

Postby Imaginethat » Thu Nov 07, 2019 10:11 am

I hate to be the one to say it... but it would have been better if you'd made your 104 degree angle out of two 52 degree angles with a couple inches between them to provide a bit of a sweep around the bend. The hard 90 will cause a lot of backpressure. You also only need 2-3" of pipe-in-the-hose. Just enough for double clamps with a 1/2" or so overlap on either side. More overlap makes alignment and insertion harder, and can make removal MUCH harder.
1974 GB 36 Classic #467 "Imagine That"
Bellingham, WA
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Re: New Exhaust

Postby StevenD » Sat Nov 09, 2019 10:36 am

Thanks for the feedback. Elbow 1.0 had 2 cuts. My geometry skill necessitated elbow 1.2. Version 1.3 got an extra 4"on one leg, but since I cut the hose to try and make 1.2 fit, the end of the outbound hose was in a different place(extra points for your alignment comment) making the angle of 1.3 wrong. I thought about two cuts for version 2.0 and discussed it with the guy at Marine Exhaust. Since the i.d. of the turbo discharge is only approx 4", the 8" dia. hose will have very little resistance from the single cut. He also wanted to put a 6" mixing bell on the end of the riser, but the muffler and tail pipe are 8" so, no go.

As to the clamps, the original elbow similarly had about 6" in the hose, and was not too difficult to separate plus the alignment/room issue is what started this exercise in the first place. Sooo, if its good enough for them ...
The folks at GB were big on overkill.
Steve D
M/V Kumatage
Hobe Sound, Fl.
GB 46 CL
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Re: New Exhaust

Postby Bella Grand » Sat Nov 16, 2019 9:46 pm

Make sure to use constant torque hose clamps at the elbow. I had an elbow actually crack due to temperature changes and traditional clamps (tee-bolt clamps or other).
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Re: New Exhaust

Postby StevenD » Sun Nov 17, 2019 10:36 am

Thanks for that suggestion. I've never noticed them on exhaust systems before, and I'm a delivery captain. I'll look into it further. The original elbow in my boat split the full length of the inside curve, starting this whole exercise.
Steve D
M/V Kumatage
Hobe Sound, Fl.
GB 46 CL
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Re: New Exhaust

Postby Bella Grand » Sun Nov 17, 2019 5:24 pm

i had several hair line cracks and you could clearly see the effects of an attempt of sealing these by over tightening. It crushed the fiberglass which, of course, made matters worse. Stuff expands when hot and that was the primary issue I had to address. Other symptoms were bubbling of the hose and blackened elbow. My EGT may be a bit warmer at 900F than that of a Lehman.
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Re: New Exhaust

Postby StevenD » Wed Nov 20, 2019 8:45 am

" My EGT may be a bit warmer at 900F than that of a Lehman."
Do you have a dry exhaust system? Pray tell. Mine are Cats.
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Hobe Sound, Fl.
GB 46 CL
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Re: New Exhaust

Postby Bella Grand » Fri Nov 22, 2019 11:11 pm

Cummins 6B5.9TA It is dry til the water injection :-)
Cooling this down in the short distance to the elbow is challenging as the spray pattern must be quite intense.
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