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700 SCI Stainless Marine manifolds

Old 11-30-2021, 07:43 PM
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Question 700 SCI Stainless Marine manifolds

In the search for a new Fastech I have come across a beautiful 382 with 700 sci. The motors were just rebuilt (due to leaky headers, in freshwater too) and I want to minimize my chances of ruining the freshly rebuilt motors. The owner did not replace the headers after the leak, he just re-welded them. The boat is going to be used primarily in salt water so Instead of swapping on some CMI's for 20k, I was hoping to get some peace of mind with stainless marine's manifolds. What is the general consensus on 700's with these risers and manifolds? Do I need to reflash the ecu's due to more back pressure? While I am on the topic, how reliable are the 700's in salt? What should I be careful of ?


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Old 11-30-2021, 11:29 PM
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IMO, the Stainless Marine's will be your best replacement option for salt water use. Biggest issue is that the Merc heads will need to be drilled and tapped to accommodate the SM's.
No reason the PCM would need reflashed. The SM's should flow just as well as the CMI's.
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Old 12-01-2021, 05:34 AM
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Not Sure what Generation Stainless Marines you plan on putting on but I would almost guarantee the Gen 3's would out flow the stock CMI'S
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Old 12-01-2021, 07:16 AM
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Go with Stainless Marine, you won't lose any performance over your CMI's. Stainless is going to have a 20% increase in price soon, so don't wait too long!
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Old 12-01-2021, 09:20 AM
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How about the hardin 525/600/700 exhaust that doesnt require any drilling of the heads??

https://www.hardin-marine.com/p-8161...-12-pipes.aspx
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Old 12-01-2021, 10:13 AM
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Yes I was worried about the stainless marine manifolds fitting. I havenít heard much feedback on Hardins product for the 700ís. What are your thoughts on Hardin vs Stainless Marine
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Old 12-01-2021, 01:33 PM
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Originally Posted by Formula292fastec View Post
Yes I was worried about the stainless marine manifolds fitting. I havenít heard much feedback on Hardins product for the 700ís. What are your thoughts on Hardin vs Stainless Marine
When Stainless Marines Rott out they leak into the bilge, when regular Headers Rott out they can leak back into the Enginess.... as far as performance i couldn't tell you.
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Old 12-01-2021, 01:43 PM
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No loss of performance with Stainless Marine. Pat installed them on several of the Active Thunders that he factory maintained for customers; after the OEM CMI headers started to fail with use cracks.
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Old 12-01-2021, 06:06 PM
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I had stainless marine on a set of 700 sci’s in a 39 top gun. The boat ran just as fast as any other stock boat with cmi’s so definitely no power loss. Two new holes need to be drilled and tapped but I think it’s worth it. As mentioned if they were ever to leak, they leak externally not into the engine. Another benefit is the riser/tailpipe is all one piece and is so much easier to remove than a header, one clamp versus 8 header bolts.
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Old 12-02-2021, 06:49 AM
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I had them on my Top Gun I believe I had 38" centers and they were kinda tight, I'd try to find a set to test fit before I bought a pair. I also Powder Coated mine silver to match the rest of my engines a bit better....


Last edited by bigfarmer; 12-02-2021 at 06:52 AM.
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