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SBC header questions

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SBC header questions

Postby Akclassic » Thu Oct 12, 2017 6:20 pm

So I had a 383 build that's beautiful and been dyno'd and about ready to drop in the boat. However, I cannot under good conscious use the Kodiak exhaust setup. So I want to build wet headers out of short ss sbc headers. My theory is to turn them upside down, then find a downturn collector and weld in a water fitting and weld to the short headers.. anyone done this yet? I know I can buy them done, but they seriously want over 3 grand for a set... doesn't look to complicated to me, a lil welding and fitting and it should be good? For far less than 3 grand.
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Re: SBC header questions

Postby jl8jeff » Thu Oct 12, 2017 6:42 pm

The biggest danger is if any water can run back down into the engine you could do some $$$ damage. I ran the Shoenfeld jet boat headers (they're dry headers) for a few weeks until I found a set of EMI Thunder manifolds for sale. I had a set of Glenwood log manifolds but in my boat they would have been a straight shot out the transom which was too much of a risk for water backflowing into the engine so I ditched them. If you don't run fully jacketed headers, heat could be an issue as well. I really don't think the Kodiak manifolds will cost much power and my 350 sounds great with the EMI manifolds which are similar to the Kodiaks. I have my Shoenfeld headers in the parts for sale section as well.
Roughneck R1652VT with Mercury 60/45 jet
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Re: SBC header questions

Postby Akclassic » Thu Oct 12, 2017 8:11 pm

Thanks for the insight. I was just wondering if I could actually tell in a blind test which headers or manifolds were on there...i guess it would need to be a drastic change to actually notice it.. maybe I should just use Kodiak in the meantime...
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Re: SBC header questions

Postby jl8jeff » Thu Oct 12, 2017 9:03 pm

Are you going through the transom with the exhaust? Is the engine in a closed compartment? The Lightning headers or CMI E-top would be the best option if going through the transom, but like you said, they're not cheap. Any amount of exposed pipe will put out some good heat so it would need a coating or wrap to keep temps down. I ran the open headers just to get the boat up and running but a 2 minute ride and my head was ringing from the noise and the heat seemed to get trapped in the cockpit so it got uncomfortable really quick.
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Re: SBC header questions

Postby nwticerider » Tue Oct 31, 2017 10:09 pm

I am also looking for a good answer for exhaust.
Check out hi-tech from Australia. |There are kind of what you are thinking about.
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Re: SBC header questions

Postby riverboater » Thu Nov 02, 2017 1:48 pm

Having played with exhaust parts swapping many times I have been surprised by what I found. On stock engines there is not enough difference to make it worth the money. On stock engines that are bladed to allow 5g rpm you do see some differences from log to centre rise, about 150rpm depending on what log to what centre rise you chose. Now you would think that stepped up cam and cu. in. would tell a much different story, not so much. When playing with a 426 cu. in. SBC, dynode at 502hp at 5200 rpm, blades to allow that 5200 rpm. Now I did not try logs, I did start with Kodiak 3-1/2 inch and jumped up to the NEW BETTER breathing 4 inch Kodiaks, Had to use a photo tach to tell I gained about 38 rpm. Then I had a chance to try water cooled through transom headers, looked SHARPE and really looked fast just sitting still. Didn't make a full 100 rpm over the 3-1/2 Kodiaks. Some time later I stuck a set of automotive dry headers mounted upside down over the transom. Now with no water and the ability to change collector size and length I was able to suck almost 400 rpm over the 3-1/2 Kodiaks. that was almost 20 years ago now and my ears are still wringing. In my opinion there are better manifolds available but not enough for me to spend full retail. Used performance exhaust can be a tricky purchase as hot things crack. you see a bit of thru transom header and centre rise on outlaws web site in the classifieds. The offshore powerboat face book page is full of high end exhaust for sale, but again now you are adding salt water to the used equation.
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Re: SBC header questions

Postby Akclassic » Thu Nov 02, 2017 11:56 pm

I pretty much came to the conclusion there's not enough torque or hp to be saved to justify the time and effort to build wet headers. The money would be better spent on a Weiand 144 ! In reality on a 475hp motor I expect to lose a max of 30hp and even less torque. I'm ok with that. Fwiw I do have A dog house and currently wet Kodiak manifolds. So heat and vapor lock would be an issue.
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